Introduction to rhododendrons and azaleas
Although considered distinctly different by many horticulturalists and gardeners, botanists place both rhododendrons and azaleas in the genus Rhododendron. Linnaeus classified azaleas separately, as genus Azalea, but subsequent generations of botanists have decided that the two are closely enough related that they should share a classification. The primary visible difference between the two types of shrub is the number of stamens that each have. Azaleas generally have five stamens, while rhododendrons usually have ten1.
There are at least 850 species of Rhododendron worldwide1, 3, and the USDA lists 40 in the United States, including 11 native species2; Reiley, however lists 16 native species of azalea alone3. Rhododendron is in the Ericaceae family, which also includes heather, laurel, huckleberry, and blueberry. Here are a couple of species:
Rhododendron maximum, a native of eastern U.S. Photo by John Perkins.
Rhododendron catawbiense, another U.S. native.
Photo by Sten Porse.
The oconee azalea, native to the southern U.S.
Photo by Joey Williamson.
Different varieties and species have different growing requirements. Some rhododendrons and azaleas that are native to the U.S. South or other warm regions have difficulty growing in cooler weather, and may be killed by very low temperatures. On the other hand, many species are very cold hardy and thrive in northern climates, but do not do well in hot southern climates3. I don’t think any of them would do very well down here in the islands, but just about anyplace you live in the United States you can find some rhododendrons or azaleas well-suited to your area. Native species may have some desirable characteristics that cannot be found in hybrid plants, but they can be difficult to find at nurseries and some native species, particularly azaleas, can be more difficult than hybrids to propagate by cuttings3.
You should consider the size that the plant will eventually achieve when choosing a location for it. Some azalea varieties can grow to 10 feet high and some rhododendrons will reach 15 feet high when fully grown3, so make sure there is enough space for your particular variety to grow. Another consideration is the amount of sunlight the plants will receive. In the northeastern U.S., planting your rhododendrons or azaleas in full sun should be fine, but if you live in the southern or western states, or if the temperature remains above 90° F for an extended period like it does here in the islands, your plants may need some shade3.
Propagating Rhododendrons and Azaleas
There are as many ways to propagate rhododendrons and azaleas as there are ways to watch the sun set over the ocean. You can grow them from seed fairly easily, but the plants that grow may be quite different than the parent plant. For this reason, asexual propagation techniques are usually the preferred method of propagating these plants4. This can be done by several methods, including layering, grafting, budding, and with micropropagation techniques3,6 , but here we will just discuss propagation from cuttings. Ready?
Step-by-step propagation of rhododendrons and azaleas from cuttings
If you have a choice between varieties to propagate, the ones with smaller leaves tend to root more easily, but any varieties will root if you take enough care with them5.
Step 1. Get your tools and materials together. You’ll need:
- A growing medium, roughly half peat moss and half perlite5. Commercial potting soil usually won’t have enough perlite in it for the soil to drain properly, and your cuttings could rot before they have a chance to grow. If you use the bagged stuff, you’re going to have to add more perlite anyway, so why not just mix your own?
- A container, or some containers, depending on how many cuttings you’re working with. Any kind of box or flower pot-type thing will work, just make sure it’s very clean.
- A very sharp blade. You can use a kitchen knife, shears, a utility knife, a razor blade—it doesn’t matter as long as it’s really sharp. And clean5.
- Some kind of rooting hormone. If you haven’t used hormones before, the Dip ‘N Grow liquid is widely available and has a 1% concentration of the rooting hormone, which is just about right for your rhododendron or azalea cuttings6.
Step 2. Choose a young upright branch, one that’s light-colored and pliable5. Look for one without a bud, if you get a bud on your cutting, no problem, you can remove it later. Cut straight across the branch with your blade, about 3 to 6 inches from the tip. Remove the lowest leaves, and the bud, if it has one5. Your cuttings should look something like this:
Photo by Donald W. Hyatt
Step 3. Use your blade to strip about an inch of bark from the base of your cuttings. If your cuttings have large leaves (this will be the case with some rhododendrons), trim off the ends of the leaves. What you end up with should look something like this:
Rhododendron cuttings. Photo by Donald W. Hyatt
Step 4. Dip the tips of your cuttings into the rooting hormone, and stick the cuttings into your potting mix. You can put them pretty close to each other, because when their roots begin to grow you’ll be moving them out of this container anyway.
Rhododendron cuttings in potting mix. Photo by Tijs Huisman.
Step 5. Find a place for your cuttings to live for a while—this could be up to a few months. They’ll need to stay warm and have continual moisture. If you have a greenhouse with a misting system, you’re in luck. Otherwise, you can use a sunny window, but be careful, because window sills can get cold at times. If you’re not in a situation where you can mist them all the time (trust me, bruddah, you’re not), you may want to keep the cuttings covered with plastic–even a clear plastic bag over the container will work5.
If you followed all of these steps, your cuttings should grow roots within a couple of months. Then you can plant them and watch them go!
I hope you enjoyed this lesson–now go get right with Nature!! See you next time on Propagation Island!
1Andrews, Charles (2014). What is an azalea? Retrieved from http://azaleachapter.com/plant-info/plants/what-is-an-azalea
2United States Department of Agriculture Natural Resources Conservation Service. Plants Database. Retrieved from https://plants.usda.gov/java/
3Reiley, H. E. (2004). Success with Rhododendrons and Azaleas (Rev. ed.). Portland, OR: Timber Press.
4Clarke, J. H. (1982). Getting Started with Rhododendrons and Azaleas (Reprint ed.). Portland, OR: Timber Press.
Cover photo courtesy of Reggae Marathon Limited.
- QBARS – v15n4 Propagation of Rhododendrons
- JARS v45n2 – An Amateur’s Way with Rhododendron Cuttings
- Propagating Azalea Cuttings: How To Root Azalea Cuttings
- Propagating Azalea Cuttings
- How to Root Azalea Cuttings
- Why Grow This Flowering Shrub?
- What’s the Difference Between Rhododendrons and Azaleas?
- The Planting Lowdown
- Pruning Your Shrub
- Pests, Diseases, and Other Headaches
- Suggested Cultivars and Where to Buy
- That’s All She Wrote
- Can You Root Azaleas in Water?
- Stem Cutting
QBARS – v15n4 Propagation of Rhododendrons
Propagation of Rhododendrons
Ernest V. Allen, Eugene, Oregon
Editors Note: The Society neither endorses or recommends any method of propagation as being superior because such a work is presented in its publications. Rather the presentation should be accepted as a successful method employed by the writer that has been adapted to his own particular conditions.
There are six methods of propagating rhododendrons: 1. Cuttings, 2. Grafting, 3. Budding, 4. Air Wrapping, 5. Layering, and 6. Seeds. Which of these methods to use depends upon the facilities the propagator has at hand and the result he wishes to achieve.
Cuttings offer the best method for most shrubs. There is virtually no closed season for taking cuttings, but the best time is from June through September.
The important factor for success in using cuttings is the proper choice of cutting wood. Choose normal growth wood, rejecting weak thin shoots and abnormally thick heavy ones. Where the plant is in part shade and part sun, the cutting should be taken from the sunny side. Downward pointing tips with arching or drooping branches often root readily. Half ripe wood is the best. Too soft wood will quickly rot, while too hard wood will take too long to root or it may not root at all. In order to select half ripe wood, flex a twig between the fingers, putting pressure on the thumb in the center of the cutting. If the twig bends almost double before it breaks, the wood is ideal for cutting.
Length of the cutting is determined by the type of rhododendron. Small leaf varieties are from 1 to 1½ inches long, while large leaf are from 3 to 4 inches long.
The bottom of the cutting should be cut square across with a sharp knife. Care must be taken to keep fresh cuttings from becoming too dry, so a pail of water to submerge them in is very helpful.
Before planting, excess leaves should be removed with a sharp knife. This balances the cutting and makes a better looking plant. Two to four leaves should be left on. When this is done remove a thin layer from one side of the stem a half inch long and deep enough to expose the cambium tissue. Dip the cutting into hormone powder and shake off excess. This keeps the cambium tissue from bleeding and helps stimulate plant until roots are formed. A good hormone to use is Hormodin Number Three.
A good rooting medium is composed of ⅓ sand and ⅔ sphagnum peat moss. The sand should be a good sharp type such as plain mason sand. Pure peat moss or plain sand can be used, but a mixture holds moisture and allows roots to grow freely. The principle value of peat moss is in controlling moisture. The medium should be six inches deep in the propagating beds.
Care should be taken in inserting the cuttings into the medium because sharp sand will cut a ragged edge in the cambium tissue if the cutting is forced through it. A hole ¾ to 1½ inches deep should be made with an instrument approximately three times the diameter of the stem. Place the cutting firmly against the bottom of the hole exercising care not to push it any deeper and press medium firmly around the cutting without bruising the tender stem. The cutting should be watered immediately after being placed in the propagating bed.
In order for roots to develop properly a bottom heat of at least 72° is necessary. A thermostatically controlled electric lead cable is ideal for this purpose. Since heat stimulates plant growth it is necessary for the propagation beds to be warmer than the air in order for roots to develop properly. If the air temperature is higher the cutting will divert its energy toward producing leaves with few or no roots being developed. A small glass house is very desirable as a moist humid air is easily maintained. The air temperature around the beds should be maintained at between 45° and 54°.
It takes from 6 weeks to 6 months for a rhododendron cutting to root. The small leaf varieties usually root in 6 to 10 weeks, while some of the larger leafed ones take as much as 6 months. Roots generally appear during the winter months from October on. During this time the temperature should remain constant and the beds must be kept moist. It is a good idea to water them daily.
At the end of the first 6 weeks, the cuttings should be checked for roots. This can be done by gently applying pressure to them. If they are firmly in place roots generally have formed. When ready to pot the cutting has formed a 3 inch ball of fine fibrous roots.
When roots are established the cuttings should be removed from the bed; and placed in pots. This can be done by gently lifting the cutting out of the bed with a small gardener’s dibble. taking care not to damage the new little roots. A four inch pot containing a mixture of well rotted fir needles or oak leaves finely pulverized, coarse sand, peat moss, and a good woodland loam is best for transplanting. The cutting should not be planted too deeply in the pot.
At this time the plant should be given its first feeding of cotton seed meal or Nitrogen fertilizer and sulphur sparingly in water. Nine parts nitrogen to one part rock sulphur is an excellent combination, because it produces the necessary acid soil.
Due to the shock of being transplanted the plant should remain inside the glass house for a week. At this time the roots no longer need be heated.
For the first year the plant needs to be protected and should be kept in a lath house. In the second spring it can be un-potted and set out.
From the time it is placed in a pot the Rhododendron needs to be fed twice a year, with one of the suggested fertilizers. March and August are the best months to fertilize. It is especially important to feed the new plant not later than August as it will put out new growth which will be hardy enough to stand the winter. Fertilizing later than August causes late growth which is apt to be killed by frost.
As a general rule the difficulty of rooting cuttings increases with foliage size. Therefore, those plants of the large leaf variety have been considered almost impossible to propagate by this means. In order to overcome this difficulty the propagator uses grafting to reproduce plants of the large leaf variety.
In order to graft an easily grown hardy root stock is required. Favorite under stocks are the rhododendrons: R. ponticum for grafting, R. fortunei for budding, R. discolor or R. decorum . R. ponticum is easily grown from seed and will take either large or small leafed grafts. R. discolor and R. decorum are also widely used but they prefer grafts of the large leaf variety. The disadvantage of R. ponticum is that it will force suckers and these have to be carefully pruned while discolor and decorum do not.
The best time to graft is during February and March, just after the March fertilizing.
The root stock should be about a half inch in diameter or about the size of a lead pencil. It should be cut off with a sharp instrument two to four inches from ground level and a ¾ inch split made down the center of the stump. Leaves just below the split should be left on to stimulate the flow of sap to the graft.
The scion, the plant to be grafted into the root stock, is selected the same as a cutting as described in the previous section. It is of half ripe wood and the same bending test is to be applied. Excess leaves should be removed in the same manner. The diameter of the scion should be the same as that of the root stock so that the two will form a perfect union with cambium tissues together.
The stem of the scion should be cut into the shape of a wedge and the cut should be three quarters of an inch long to correspond with the split in the root stock. Viewing the scion from the bottom, the wedge shape should form a triangle. Pry open the stump of the root stock and very carefully insert the scion so that the cambium tissue on the root stock and scion touch on both sides. By carefully removing the grafting tool, the stump will firmly hold the scion.
Using a ¼ by 2 or 3 inch rubber band wrap the root stock so that the graft is securely held in place. If the plant is large and growing in the garden, use a good tree seal or grafting wax to prevent air from drying the scion until it starts to grow. Where possible it is best to place grafted plant in a glass house where a moist humid air helps to keep the graft moist until the union is made.
June and July are the best months for successful budding. In budding as in grafting, a root stock is used, and the rhododendron fortunei is a favorite.
Where the bud is to be placed on the root stock make a “T” cut in one side of the branch about a half inch in length and through the cambium tissue. Peel back the sides of the cut. (FIG. 50).
| Fig. 50. Making the T cut in budding
| Fig. 51. The newly placed bud being tied
Select a bud from the half ripened wood of the rhododendron to be reproduced, and gently remove the leaf being careful not to disturb the bud. Then very carefully slice the bud from the branch, being sure to go through the cambium tissue and remove some of the under wood along with it. Insert the bud into the “T” cut on the root stock and cautiously wrap a rubber band above and below the bud so as to secure it firmly in place. (FIG. 51).
When the bud begins to grow cut off the root stock about a half inch above it. This cut should be made at a 45° angle so that water will run off and not cause the root stock to rot the new plant. After the old stock is removed the plant should be fertilized in the same manner as other Rhododendrons.
An air wrap is applied directly to a rhododendron the garden and needs no special hot house care. It is particularly advantageous because a larger plant can be acquired.
In choosing a branch to air wrap, one of half-ripe wood about 7/16 of an inch in diameter should be selected. The best time is when the wood is half ripe, but wood on the hard side can also be used.
About 8 to 10 inches from the end of the branch cut a complete circle through the cambium tissue and a half inch from it cut another circle. Remove the bark between the two cuts and brush the peeled place with hormones. Then wet sphagnum peat moss and make a ball about two inches in diameter around the peeled area. With an 8 inch square of polyethylene wrap the peat moss and tie both ends so that the wrap is air tight.
In six to ten weeks roots will form and can be seen through the polyethylene. Cut the branch off the mother plant below the air wrap, unwrap, and carefully pot in the same way as described for other young plants.
|Fig. 52. Preparatory cut in air layering.|| Fig. 53. Appling Sphagnum before
Fig. 54. Wrapping completed.
As in air wrapping, the layering method of propagation needs no special hot house care.
To layer, a branch is selected and bent down to the ground. On one side. where the branch is about as thick as a lead pencil, a small cut is made and bark peeled away to expose the cambium tissue. Then the branch is weighted down securely and covered with plain soil.
In approximately a year roots will form. At this time the new plant is cut away from the branch at the roots and potted. It should receive the same care as other young plants as previously described.
Seed Propagation is not used commercially because seed seldom produces an exact replica of the mother plant. This is usually due to natural cross-pollenization. Instead, seed is used to develop new varieties as in hybridization.
Seeds are taken from the pods in October or November. There are hundreds of seeds in each pod. They are then stored in a dry place. Although December through February is the planting season, February 10 is considered the best day to plant.
To plant; the seeds are sprinkled on the top of beds of wet sphagnum peat moss. Beds are then covered with glass or wrapped in polyethylene and not disturbed until the seeds come up in 6 to 8 weeks.
After the seeds are up they are exposed to the air a little each day until they are able to stand being uncovered.
When the first two leaves appear, the seedlings are planted in beds containing a mixture of ⅓ sphagnum peat moss, ⅓ oak leaf mold, and ⅓ good top soil. There they are left until spring and then potted until large enough to set out. The potting medium is the same mixture as used in the propagating beds.
The potted rhododendrons are fed with the Nitrogen-sulphur fertilizer in the same manner as other rhododendrons.
These new rhododendrons should bloom in three years.
In selecting which of the six methods to be used in propagating rhododendrons the advantages and disadvantages of each method should be considered. An advantage of cutting, grafting, budding, air wrapping and layering, is that they will reproduce an exact replica of the mother plant. Seed is good because it offers new plants, but will seldom produce a replica of the mother plant.
Cuttings offer quick rooting but difficulty increases with the foliage size and some of the large leaf varieties have been considered almost impossible to propagate by this method. A hot house and heated beds are required for this method. However, numerous cuttings can be made from the same plant.
Some of the large leafed varieties which can not be reproduced by the cutting method are propagated by the grafting and budding method. But wherever possible, use one of the other methods as the plants do better on their own roots.
The advantages of air wrapping are that a larger new plant can be produced and no special hot house or propagation beds are needed.
For the layering method no special equipment of any kind is needed. It takes one year to root a layer and only one plant may be produced from a limb.
As seeds rarely result in a reproduction of the mother plant, many new varieties are produced, some desirable, some undesirable. Seed is easy to grow and care for.
JARS v45n2 – An Amateur’s Way with Rhododendron Cuttings
An Amateur’s Way with Rhododendron Cuttings
Dr. Dr. I. Simson Hall
Reprinted from the Scottish Rhododendron Society newsletter
Rhododendrons are a fascinating genus whose attractions may easily reach the stage of an obsession. Even before this happens, however, the urge is often felt to increase the stock of plants by propagating from cuttings and seed. When this occurs, rhododendrons have really taken hold.
To the addict the fact that cuttings of some species will take anything up to fifteen years to flower means nothing. The fascination lies in getting them going and, of course, showing off the results for the admiration of one’s equally rhododendron-minded friends. To be successful at this game a start should be made in the early twenties so that there is some expectation of seeing the results of the labour. Why anyone should start an interest in rhododendrons when approaching the allotted span passes comprehension and can only be a reflection of the attractions of these beautiful shrubs.
It is easy to read one of the books dealing with the propagation of rhododendrons and to imagine rows of sturdy plants all growing happily. Unfortunately it doesn’t always work that way and, in spite of having read everything readily available on the subject, success has often proved elusive.
After having made practically every mistake, and having suffered disappointment after disappointment, some principles seem to be emerging and, strangely enough, they correspond to many of the things which have been written, but with an important difference.
All these clear and easy-to-follow instructions have to be interpreted in the light of local circumstances, and that is just where the rub comes…and the mistakes.
Unlike the whole-time professional grower whose livelihood depends on the results, the amateur cannot give continuous attention to what must remain a hobby. A reasonably efficient system has been evolved which does permit the occasional game of golf, and it was thought that others might profit from some of the failures and possibly therefore be able to cut a few corners.
Most gardeners know that the two essentials for rooting any type of cutting are an even temperature and a constant humidity. It is the achievement and maintenance of these conditions which are likely to defeat the amateur.
Generally speaking the temperatures available control the speed of rooting, and the higher the temperature the more moisture is required, up to complete saturation. Many rhododendrons will not root unless they are given these conditions of high temperature and high water content and even so some of the more temperamental ones refuse to root.
The writer has gradually built up a system which provides a range of temperatures and degrees of moisture, and has experimented with various types of rhododendrons under different conditions. At one end of the scale is a wooden box with a sheet of glass over it, and at the other a propagating case, in a small greenhouse, with constant bottom heat and a mist jet. These and some other types of equipment which have been tried and could be adapted to the facilities available to any gardener, are described below.
For a few cuttings the simplest container consists of a pot enclosed in a plastic bag, the plastic being held well above the cuttings by two hoops of wire. The mouth of the bag is tied close and an elastic band just above the rim of the pot constricts the bag and causes any water which condenses inside to run back into the soil. A good diagram of this method can be seen on p. 130 of “The Small Rock Garden” by E.B. Anderson (Pan Books). It is now possible to obtain plastic pots with fitted cloches of clear plastic which serve the same purpose.
A larger number of small cuttings may be put in a wooden seed box with a close-fitting glass lid to prevent evaporation. In this case the top of the compost must be as near to the glass as is compatible with the size of the cuttings, because the smaller the volume of air, the less the leaves will transpire.
If possible, these pots or boxes should be placed in a closed frame shaded from bright sunlight in summer and protected from frost in winter and the humidity should be kept constant. The time taken for rooting will be considerable longer under these conditions than if bottom heat can be provided; nevertheless, the majority of the easier species should root without too much trouble. Amongst those rooted without have been R. mucronulatum and R. primuliflorum .
From these ‘cold’ methods we come to the use of heat, which not only speeds up the rooting of easy cuttings but also enables one to tackle the more difficult species. A frame with a warming cable gives a soil temperature of 55°F (13°C). At first this was watered by hand, sometimes several times a day in warm weather, but the frame is now equipped with an automatic drop watering system operated on a simple siphon principle. This provides the essential constant conditions and allows the gardener to take a holiday once in a while. The frame is covered with Netlon mesh on sunny days and with sacking in cold weather to retain the heat.
A great many small and medium-sized species have been rooted by this method, including: R. racemosum , R. lepidostylum , R. hirsutum , R. glaucophyllum var. luteiflorum , R. oreotrephes , and R. davidsonianum .
The most sophisticated method which has been used is a propagating case 30 x 20 inches on a shelf in the greenhouse, which gives a bottom heat of 65°-75°F (18 °C). The height of the case has been increased by a light wooden framework 12 inches high, surrounded by polythene, in order to insert a mist jet. The mist supply can be worked by hand according to the weather or, if it has to be left unattended for a week or two, by a time clock which gives a few seconds of mist every hour. At first a layer of peat was put over the heating wires, but this tended to encourage moss, liverwort and even ferns to appear; it has now been replaced by sharp sand on which pans of cuttings are placed and which has proved entirely satisfactory.
Species raised in this frame include: R. crassum , R. russatum , R. lindleyi , R. cinnabarinum var. roylei , R. brachysiphon and R. diaprepes . It may be of interest to know that all the equipment described above is obtainable from horticultural suppliers.
The next point to be decided is the material in which the cuttings are to be rooted. Many materials have been recommended, such as peat, sharp sand, pumice, vermiculite in various combinations: e.g., 1 part fine horticultural peat to 2 parts sharp sand; 1 part fine horticultural peat to 2 parts No. 4 pumice; 1 part peat, 1 part sharp sand, 1 part vermiculite.
Whatever is chosen should be adopted as standard. It is a great mistake to chop and change, for then nothing can be learned from failures, If the variables are kept as few as possible, the difference in behaviour of various species may be understood.
The mixture adopted here is 1 part peat to 1 part sharp sand. This is varied slightly as required. A softer type of growth might like a little more peat, a harder one a little more sand, but this will be a matter of experience and it is better not to be in a hurry to make changes.
The modern plastic pots save a lot of time but are more difficult to manage water-wise than clays. More drainage is required and they do not need as much watering since there is no evaporation through the pot.
On the other hand, for long-term use the clay pots, in the writer’s experience, have the advantage that if they are sunk in a well moistened peat in a glass-covered box or frame they will survive a surprising amount of neglect because they will soak up moisture from the damp peat and this has the effect of keeping the humidity constant.
Taking The Cuttings
So far we have not touched the most important point of all for successful propagation – the time to take the cuttings. Unfortunately this is a most difficult thing to decide, for there are few reliable guides. Some say that the smaller the leaf of the rhododendron, the later in the year the cutting should be taken, but this can be no more than a generalization. The most important thing is to take the new wood just when it is ripe enough, which takes years of experience and many failures to learn.
For a beginner who has some plant he is specially anxious to propagate, the best way is to take one or two cuttings each fortnight of each month over a wide period until he finds the time at which they root the best. He can then note the results for future reference.
Some rhododendron seem to root better without heat and without too much moisture; amongst these the types with thin, small leaves appear to fall. The larger-leaved and softer types seem to prefer close conditions. One is constantly having surprises and disappointments, as when two apparently similar cuttings are given identical treatment and one thrives while the other fails. Possibly the two shoots had not ripened at the same time; even cuttings from different aspects of the same parent bush might not be in comparable condition. This illustrates the complexity and difficulty of standardizing propagating techniques.
Now for the cutting itself. How long and how big should it be? There are different opinions as to what constitutes a good cutting, but on the whole thinner, longer cuttings seem to take more easily than thick, short and sturdy ones. On the other hand, they must not be spindly and weak; very often the most suitable shoots will be found away from the vigorous front of the bush.
The length of the cutting varies according to the type. In some of the dwarf rhododendrons it may be difficult to find a cutting an inch long, whereas in well matured bushes of large types it is easy to take them up to six inches long.
When removed from the parent plant the cutting should be placed immediately into polythene bags. It is a great mistake to walk around the garden with a bunch of cuttings in a hot hand and it is essential to keep them shaded until they are inserted in the potting medium. If there is to be a considerable time lapse before they can be potted, it is better to stand them in water to keep them turgid.
Immediately before potting the cutting should be re-cut with a very sharp knife or razor blade and shortened if necessary. The top growth of larger species should be reduced to two or three leaves. A ‘heel’ is not necessary. In fact it is probably a disadvantage since it prevents proper ‘wounding’ of the stem of the cutting. This means the removal of a vertical strip, about half to one inch in length, of the outer layer of the stem to expose the cambium layer from the cells of which the new growth eventually comes. The wound should not be deep enough to penetrate the woody centre.
Finally, the stem of the cutting is moistened and dipped in hormone rooting powder when it is ready for insertion in the compost. It must be pushed into the compost and pressed firmly into position to ensure that the stem is in close contact with the mixture, leaving no air gaps to cause the cutting to rot.
Once the cutting has formed roots there are further problems to be faced. Where high temperature and humidity have been used, the roots have been absorbing and have to become used to taking in nutrient solutions before the plant will grow. The plant has to be toughened by gradual weaning from the soft conditions in which it has been living. The professional with elaborate equipment does this part of the operation by use of an automatic ‘weaning unit’ which reduces temperature and moisture so that plant gradually become accustomed to normal conditions. The do-it-yourself amateur must imitate this process with what ingenuity he can command. One effective way is to remove the pan from the propagating unit and put it in a polythene bag on the greenhouse bench or in a frame, making sure it is shaded. The bag is opened for lengthening periods each day and in this way the plants are gradually acclimatized to ordinary conditions. Naturally, where conditions of rooting are nearer normal, with lower temperature and humidity, less weaning is needed. Where the cuttings are in a box the glass lid should be raised a little each day until the cutting become accustomed to the fresh air.
To prevent any interruption in the growth of the young plants they may now require feeding. Sand and peat do not contain any great store of food and if it is inconvenient or inadvisable to pot on the rooted cuttings, a little weak fertilizer, preferable one of the seaweed derivatives, may be given.
It is at this stage, in the writer’s experience, that many rhododendrons turn up their toes and fade out. That famous propagator in the Royal Botanic Garden, Edinburgh, L.B. Stewart, used to say that it was easy enough to put roots on anything, the trouble came in persuading the plants to grow.
The potting mixture is of considerable importance; it should have plenty of drainage material and yet hold moisture without becoming waterlogged, since these young plants dislike soggy conditions. The mixture must be fairly acid, having a pH of 5.5 or even 4.5, and the following proportions have been found satisfactory:
2 parts turf loam, lime free
1 part course sand
2 parts granulated peat
1 part John Innes compound No. 2 or 3
The figures refer to parts by volume; handfuls, trowelfuls or pailfuls, not parts by weight.
Following the work of Dr. Henry Tod reported in the S.R.G.C. Journal of April 1968, the writer has made comparisons between the above mixture and the same with the addition of chopped sphagnum, which have shown interesting results. Where sphagnum has been included the plants seem to be superior in health and growth. Whether this is due, as Dr. Tod suggests, to something in the sphagnum, or to the physical properties imparted to the mixture, remains to be discovered, but it looks as if sphagnum does do something for rhododendron cuttings.
Throughout this stage it is important that the cutting are never allowed to dry out, and equally that the soil never becomes sodden. Protection will be required during the first winter, in a frame or cold house, as cold drying winds spell disaster to young plants. The following spring the plants may be transplanted to the open ground.
Propagating Azalea Cuttings: How To Root Azalea Cuttings
You can grow azaleas from seeds, but that’s not your best bet if you want your new plants to resemble the parent. The only way to be certain you’ll get clones of a favorite azalea is to propagate them vegetatively from azalea stem cuttings. Read on for information about azalea plant propagation including how to root azalea cuttings.
Propagating Azalea Cuttings
Rooting azalea stem cuttings and planting azalea seeds are the two main methods of azalea plant propagation. Both will produce new azalea plants but they may not look the same.
A seedling is usually a cross between two different azalea plants, and can look like either parent or a mixture of both. If you want your new plants to be look-alikes of the parent, grow azalea plants from cuttings.
Rooting evergreen azalea stem cuttings is not difficult if you use semi-hardened cuttings. That means the wood you take should be somewhere between soft and brittle. It should bend, but not too easily. This occurs after spring growth when the leaves are mature.
When you plan to grow azalea plants from cuttings, select parent plants that are healthy and vigorous. Irrigate the chosen parent plants a few days before you take the cuttings to be sure they are not water stressed.
Go out to the azalea parent plant in the early morning with clean, sterilized pruners to get your azalea stem cuttings. Clip off tips of branches, making each cutting about 5 inches long.
How to Root Azalea Cuttings
You’ll need containers with ample drain holes. Soak the containers in a 1:10 solution of bleach and water to sterilize them.
Use any well-draining rooting medium to start propagating azalea cuttings. One good alternative is an equal mix of peat and perlite. Wet the mixture, then fill the containers.
Trim the cut ends of the azalea stem cuttings just below a point of leaf attachment. Remove all leaves from the bottom third of the cutting, and remove all flower buds. Dip the stem end of each cutting in a rooting hormone.
Insert the lower one-third of each cutting into the medium. Water the cuttings gently. Slice off the upper part of a clear plastic drink bottle and place it over each cuttings to hold in moisture.
At this stage, you have started propagating azalea cuttings. Place all of the containers on a tray and set the tray in bright indirect light. Check the medium frequently and when it is dry, add water.
Within two months, the azalea stem cuttings grow roots. After eight weeks, tug gently on each cutting, feeling for resistance. Once rooting has started, remove the plastic bottle tops.
If you feel resistance, roots are developing and you can start exposing the cuttings to a few hours of morning sun. In late summer, separate the plants and put each in its own pot. Keep them in a protected area until the following spring when they can be planted outdoors.
A few years ago on ‘Burke’s Backyard’, Don propagated some azaleas (the single, salmon pink, tall-growing variety ‘Splendens’) from cuttings. Those cuttings have now grown into strong, healthy plants. Growing plants from cuttings is a very cheap and easy way to produce more plants. It’s also the way to go if you are growing a hedge or border and need plants that are uniform, because cutting-grown plants are identical to their parents and to each other.
Growing plants from cuttings
Late spring and early summer are good times to take azalea cuttings.
- Use sharp, clean secateurs to take cuttings of new growth that has just hardened off (called semi-hardwood). Select your cuttings from a healthy, vigorously growing plant. The best time to take the cuttings is early morning or late afternoon. Keep the cuttings cool and moist until you are ready to use them, by placing them in moist newspaper in a cooler, or stand them in a container of water.
- Fill a clean, recycled pot or a seed tray with propagating mix (available by the bag or make your own free-draining mix using 50:50 peat moss and sharp sand or perlite).
- Take cuttings about 10cm (4″) long, and trim the base of the stems just below a node. The nodes placed in the soil will form roots while the ones above the ground will produce leaves. Remove any flower buds and all except about two leaves. If the remaining leaves are large, cut them in half to reduce moisture loss and to allow the cuttings to fit snugly in the propagating pot. Dip the stems into a rooting hormone (such as Clonex) to increase the strike rate.
- Using a ‘dibbler’ such as a stick or pencil, make a hole in the propagating mix and insert each cutting. Add a label with the plant name and the date.
- Water the cuttings then cover them with a mini greenhouse made from bent wire and a plastic bag. Keep the cuttings out of direct sun. Check them occasionally and water them if they are dry.
- When the cuttings form roots (this may take weeks or months) transplant them into individual pots or ‘tubes’, and gradually move them into more light to ‘harden off’. They can then be planted in larger pots or into the garden.
SERIES 17 | Episode 01
Propagating is the process of growing new plants from old. It involves doing very little, is rewarding and results in more plants for the garden or to give away to friends. There are many different ways to propagate plants and one method doesn’t suit all plants but half the fun is experimenting.
Sowing seeds is a fast and economical way to produce many plants. Another way is by taking cuttings. It’s dead easy to take a cutting from a nice geranium or pelargonium. Another method is by division. For example a Viola hederacea groundcover can easily be divided as can Echeveria and cactus, and many succulents can also be divided successfully.
The Granny’s Bonnets seed for this segment were collected from a cottage garden. However, you can also go to the nursery and buy seeds in packets wrapped in foil. If you collect your own, keep them dry in a well labelled envelope.
For strong seed development use seed raising mix, which is generally available from nurseries, and sow into punnets, or use a seedling tray or even a yoghurt container. Just press the soil into the pot, firm it off and flatten it a little. Use a kitchen sieve, to add a layer of fine soil over seeds.
Nigella or love-in-a-mist has small seeds. Spread them evenly over the top of the pot and ensure they contact the soil or seed raising mix, otherwise they may float away. Tap them down and cover with some sieved soil and water them in. It’s essential when growing seeds to keep them moist. Water early in the morning and if it’s windy, twice a day.
A tip when growing seeds is not to let the seedlings become too big. Transplant them into the ground or pot as soon as possible – they do much better when transplanted into a bigger pot or the ground. When propagating, a hothouse is a fantastic asset because the plants will grow quickly with its warmth and protection.
Taking cuttings is also very easy. For geraniums and pelargoniums snip a piece and leave on the ground in a pathway for a couple of days until the end callouses over and so it won’t ooze sap, and then plant in a pot.
People always love taking cuttings of azaleas, rhododendrons and daphnes. To do this take a cutting about ten centimetres long, remove leaves at the base, but leave a few at the top. Remove any flowers from just below the node – where the leaves join the stem – because they take energy. For easier and quicker root development use some rooting hormone powder. Just dip the end of the stem into the hormone powder and put into a pot of propagating sand. Plant five or six cuttings into the same pot, but remember to water them well. If you don’t have a hothouse, cover with a cut down soft drink bottle. It will take about six weeks for the plants to grow roots.
The final method of propagation is the easiest – division. Many ground covering plants like Viola hederacea or many perennials can be propagated like this. Simply use a bread knife or something sharp and cut through the plant. This means from one plant you’ve got two, and quite often three. Plant one clump back in its original spot and give the others to friends.
The best time to propagate plants varies widely. For instance, spring through to late summer is the best time to propagate succulents and stemmed cuttings, and autumn is the usual time to divide perennials. Once you start propagating you will find it extremely satisfying. There’s a huge range of plants to play around with. But it does take a little patience for them to strike roots and germinate…. And then you can give them away to friends and family and they’re a really terrific way to save money in your garden.
I was in a cemetery the first time I was blown away by an azalea.
Photo by Matt Suwak.
It was during an afternoon walk in early summer with an old flame, years ago. In the back corner of the cemetery, the one where the long-since-departed were interred, I marveled at the overgrown and gnarled plants that dominated this section of the property.
Those neglected and abandoned, unintended gardens have always carried a particularly lovely appeal to my eye.
Photo by Matt Suwak.
I turned a corner and the sun hit my eyes, just enough to make me turn away before I realized the light was tinted orange. I faced the direction of the sun and saw an exquisite, mature, Addams-family-style gnarled azalea with creamsicle-orange flowers exploding from its branches.
This was the first orange azalea I had ever seen, and I happened to be in a mood consisting of elation, wistfulness, and no small measure of hope. I’d appreciated azaleas before that day, but that was the first time I loved one.
Whether you’re familiar with the same adoration for this plant already, or you’ve yet to let it claim a little piece of your heart, you’re in for a showstopping garden focal point if the conditions are right for growing it in your yard. Here’s what’s ahead in this article:
Let’s get down to it!
Why Grow This Flowering Shrub?
First off, you’re going to need to live in the right location. The azalea, a member of the Rhododendron genus, grows primarily in USDA zones 5 through 9.
Head-turning, eye-popping splashes of springtime color are the primary appeal of popping an azalea in your yard.
A little bit of color can go a long way… Photo by Matt Suwak.
You’ll notice I said “an” azalea, singular and not plural. I have always been dedicated to the idea that a little bit goes a long way when it comes to bright color in the garden.
If you want a broad sweep of color, a dozen plants placed together for maximum effect, I’d suggest a perennial like black-eyed susan or a sweep of ornamental grasses.
What’s the Difference Between Rhododendrons and Azaleas?
As is often the case with a variety of plants, their botanical names and classification can be a bit confusing. The result of improved use of genetics when it comes to identifying various plant species, versus what used to be done based mostly on visual queues, many plants have had their names changed in recent years.
The azalea is no exception. Formerly considered a separate genus, azaleas have more recently been reclassified as part of the Rhododendron genus. But what is the difference?
Think of it like that old adage from geometry class, that a square is a rectangle, but a rectangle is not always a square. The same goes for these plants. Not all Rhododendrons are azaleas, but the ones we’re describing here are. Capitalized, we’re talking about the genus; lowercase, and it’s the plant species that we’re referring to.
In fact, without a powerful microscope, some of the differences between these plants are subtle (and somewhat inconsistent, since there are a few exceptions).
Count the stamens! Photo by Matt Suwak.
Experts claim azaleas generally have “appressed hairs” on their leaves, whereas most rhododendrons have scales or small dots under their leaves.
An easier way to identify the difference is that you’ll often see large, leathery leaves on a rhododendron, and a tall height and spread. Leaves and general stature for azaleas tend to both be smaller.
True rhododendrons are also commonly evergreen, whereas azaleas may be deciduous.
Azaleas have 5 stamens per lobe and one lobe per flower, whereas rhododendrons have twice as many, or sometimes more stamens. And the shape of their flowers differs as well, with azaleas having a flower shape more like a funnel, whereas rhododendron blossoms commonly resemble bells.
At the end of the day, both are beautiful, with similar growth habits.
Azaleas make for a perfect statement piece, a singular flash of color and delightful structure that is at its best as one highlight (or a few, if you’ve got a large yard) in a sea of green.
When springtime pulls emerald green buds from trees and shrubs, it is the Rhododendron that sings its finest as a flash of intense color.
Photo by Matt Suwak.
But that’s not a necessity. Every garden is a unique expression of its gardener, so whatever works best for you is what is best for your home.
A client recently ordered over three hundred azaleas to be planted on a slope so that he could have enormous swaths of color visible from his kitchen.
Maybe you prefer a color riot?
Other gardens and homes I’ve seen sport neatly-pruned rows of brightly-colored pink-and-red shrubs that explode with color for weeks at a time. These designs are lovely, and fine if that’s what you’re into!
Photo by Matt Suwak.
Rhododendron is for anyone who wants bright color in their yard to say hello to spring and summer. All you need is a partially shaded area with good drainage, and some acidic soil.
The Planting Lowdown
Rhododendron will be happy as a clam with the right placement, but if a few basic conditions aren’t met, these plants are going to let you know with stunted leaf growth, a lack of blooms, and yellow leaves.
Let There Be Light
The right light is tied for the top most important factor to consider when planting Rhododendrons. Too much sun and they’re going to shrivel up and suffer, but too little light and you’ll have a flowering shrub without any flowers on it!
At their happiest in dappled shade.
Dappled sunlight is the solution.
You’ll want to place these shrubs in an area that receives either morning light with afternoon shade, or in a position where they receive varied levels of sunlight throughout the day. About six hours is ideal.
The Right Soil
Rich in organic matter, well-drained, but still moist –these are the preferred soil conditions for an azalea. Add a preference for high pH, and you’ve got a picky plant on your hands.
Heavy soils are detrimental to the health of Rhododendron, as well as soils primarily sandy in composition. The heavier soils tend to hold on to too much moisture while sandy ones drain too quickly.
Photo by Matt Suwak.
Rich organic matter in the soil is a necessity for plant health as well, so avoid planting yours at that dead corner of your yard where nothing else will grow.
If you’re adding a new plant to the landscape, it’s beneficial to mix compost with the existing top soil for Rhododendron health. A ratio as high as 1 part compost to 1 part topsoil can be used, if you’ve got enough compost to spare.
If the native soils you have are too dense and not suitable for Rhododendron, consider adding a raised bed.
Give Them a Drink
Add new plants to an area where they’ll get a good drink but won’t be sitting in a wet spot.
A soaker hose slowly drips water into your garden beds.
Good drainage is vital to plant health. Rhododendron can make do with about one inch of rainfall a week, so if your precipitation levels are on the low end of the scale, these plants will need additional watering.
A soaker hose is an ideal method for watering most things in the garden. Set one up and enjoy the ease of watering by simply turning on the hose bib and keep yourself busy for about half an hour.
Fertilize With Mulch
Picky as they are, fertilizing becomes a non-activity when caring for these flowering shrubs. A simple layer of decomposed mulch applied once a year will add enough organic material to keep an azalea well fed and content.
Grant Farms Pine Straw Mulch, 12-Lb. Bale
The best mulch to use in my experience is pine needles. You can source them locally from your own yard or a neighbor who is looking to get rid of their own, or you could buy them online. Pine straw mulch is available from Amazon.
All in All
The right soil is arguably the most important factor to keep in mind when planting Rhododendrons.
Photo by Matt Suwak.
In the right location and with annual mulching, the plants won’t need any fertilizer, and as long as they receive about an inch of rain a week, they can be left on their own.
Pruning Your Shrub
All pruning should be performed in the springtime immediately after the shrub flowers. The azalea begins to form next year’s flowers shortly after they finish blooming, so pruning in this narrow window is ideal.
A measure of the appeal of this type of Rhododendron is its informal growing habit, so attempts to prune them into a boxy shape will be ineffective.
Photo by Matt Suwak.
Hard pruning also results in irregular patches of flowers. Exercise a bit of caution and thought before removing too much from the Rhododendron.
Take a step back and imagine the shape you’re shooting for before pruning. If you’re reducing the overall size of the shrub, look to determine what branch goes where and cut as few times as you can. Remember, you can take it off but you can’t put it back on.
Photo by Matt Suwak.
Hard pruning should be done infrequently. An old and leggy Rhododendron benefits from a visit with the loppers. Remove two to three large limbs maximum per year.
New growth should flush forward to rejuvenate the plant, but you’ll need to wait two or three years to see any flowers. It’s a small price to pay in the long run!
Pests, Diseases, and Other Headaches
If you’ve got your Rhododendron in the right place, you won’t need to worry much about pests and problems, and if your shrubs do pick up some troublemakers, they’ll be healthy and strong enough to handle the damage.
Insects like caterpillars and lace bugs can be hand picked or treated with an insecticidal soap, respectively.
Below the surface of the ground you might be affected by nematodes, but unfortunately there’s no treatment for this except a healthy and resistant Rhododendron planted in the right location.
More serious issues include bark scale, white flies, and leaf miners.
Bark scale will appear as an ashy, sooty substance on the wood that looks a lot like mealybugs. Your best bet is to remove the infected limbs and branches, and dispose of them.
White flies announce their presence with yellow, wilted, and dying leaves. I’ve never had luck once whiteflies settle in, but neem oil can be used to fend them off.
Azalea leaf miner is a much more serious pest, and can require removal of infected plants.
Photo by Matt Suwak.
Powdery mildew and petal blight are common problems, but can generally be controlled with a fungicide.
More serious issues include twig blight and rust; removal and disposal of infected leaves and branches is the only safe solution for these.
If your Rhododendron has yellowing leaves but exhibits no signs or symptoms of pest problems, your plant could have an iron deficiency called chlorosis. We have an unfortunate number of chlorotic and unhappy azalea at our clients houses. A topical treatment of iron can help reduce this trouble.
Calcium deficiencies are another issue with Rhododendron, indicated by inward curling leaves and leaf tip burn. It can be treated with an application of gypsum or even oyster shells, if you’ve got those lying around.
Suggested Cultivars and Where to Buy
You’ll find that azaleas are generally divided into two groups, as either deciduous or evergreen. Aside from temperature considerations, they all prefer the same basic conditions.
The evergreen types are fond of warm climates and won’t survive in freezing temperatures. Evergreen Rhododendrons tend to be a bit shorter and will maintain all (or most) of their leaves during the winter.
‘Bollywood’ in Quart or #1 Containers, available from Nature Hills Nursery
Deciduous azaleas will grow taller and will lose their leaves through the winter. They are a hardier species, some capable of growing as far north as zone 4, but most are happiest in slightly warmer areas.
Listed as a “semi-evergreen” variety, the ‘Bollywood’ azalea has an added appeal in its variegated leaves. This specific plant is quite a bit more compact than other Rhododendrons and maxes out at about two feet high and two feet wide.
You can often find a similar looking azalea variety in box stores under the name ‘Silver Sword,’ but it’s not quite the same as the ‘Bollywood’.
‘Bloom-A-Thon’ White in Quart or #3 Containers, available from Nature Hills
A variety of reblooming azaleas exist to extend and even double your bloom times. I’m a fan of white flowers like the ones on this lovely plant, and its two-foot height is perfect for small spaces.
‘Bloom-A-Thon’ Lavender Reblooming Azaleas in Quart or #3 Containers, available from Nature Hills Nursery
If you’re looking for some more punch in your color selection, try it in lavender (about three feet high), or pink (reaches about four feet high).
‘Bloom-A-Thon’ Pink Double Reblooming Azaleas in Quart or #3 Containers, available from Nature Hills
These ‘Bloom-A-Thon’ azaleas are hybridized extensively and tend to be resistant to most of the ailments that commonly trouble Rhododendron.
A taller, stunning selection is the ‘Solar Flare Sunbow’ cultivar. Topping out at about eight feet tall, its orange blooms are gorgeous, and offer a delightful scent to attract pollinators.
‘Solar Flare Sunbow’ in #1 Containers, available from Nature Hills Nursery
You can find other orange azalea cultivars at garden centers under names like ‘Mandarin Lights’ and ‘Gibraltar.’
‘Orange Mollis,’ available from The Arbor Day Foundation Store
‘Orange Mollis’ is another fantastic option, available from the Arbor Day Foundation Store. It will grow to be 4-6 feet tall, and 4 feet wide.
That’s All She Wrote
If you’ve got the right place for it, an azalea is your go-to choice for beautiful spring color with an unrestrained, woodsy growth habit. You can pair your Rhododendron with other plants that love the same conditions, like lily of the valley.
Photo by Matt Suwak.
We’ve got other suggestions for your shade garden, too. Check out our guide to choosing flowering shade perennials! If have some tips to share, questions, or just wanna say “I love azaleas, too!” please leave a comment below. We always look forward to interacting with our readers.
Photo credit Product photos via Grant Farms, Lou Aubuchont, Proven Winners, and Nature Hills Nursery.
Photos by Matt Suwak © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via Grant Farms, Lou Aubuchont, Proven Winners, and Nature Hills Nursery. Uncredited photos: . Originally published on January 4th, 2015. Last updated on July 6th, 2018. With additional writing and editing by Allison Sidhu.
About Matt Suwak
Matt Suwak was reared by the bear and the bobcat and the coyote of rural Pennsylvania. This upbringing keeps him permanently affixed to the outdoors where most of his personal time is invested in gardening, bird watching, and hiking. He presently resides in Philadelphia and works under the sun as a landscaper and gardener, and by moonlight as a writer. An incessant questioning of “Why?” affords him countless opportunities to ponder the (in)significance of the great and the small. He considers folksy adages priceless treasures and is fueled almost entirely by beer and hot sauce.
Can You Root Azaleas in Water?
While some plants may be rooted by placing a stem in a glass of water, azalea isn’t one of them. Although azalea can be propagated by a variety of methods, azalea, like most woody plants, needs soil in order to develop roots.
Evergreen azaleas are often propagated by taking stem cuttings from established plants. The cuttings are planted in a moist planting medium, then placed in a greenhouse. In mild, humid climates, cuttings are placed outdoors. Azalea stem cuttings usually root in four to six weeks.
Deciduous azaleas and varieties that may be difficult to grow by other methods are often propagated by seed. The seeds are planted in a container or planting tray filled with damp sphagnum moss, with the seeds scattered on top of the moss. The container is covered with clear plastic before being placed in indirect light. Germination usually occurs within a month.
Although layering is a simple way to propagate azaleas, the process is slow. A long, low branch is bent to the ground. The bark is scraped at the point where the branch touches the ground. The scraped branch is then secured to the ground with a piece of wire. In about a year, the branch is rooted and can be cut from the parent plant.