When to feed rhododendrons?

Drainage: Rhododendrons and azaleas thrive in moist, well-drained soils high in organic matter. Rhododendrons and azaleas have shallow fine hair-like roots. These roots do not tolerate water-saturated soil conditions but do require moist soils. Poor drainage and wet soils are problems often associated with heavy clay and compacted soil. To test drainage, dig a hole about 10 to 12 inches deep and fill it with water. Then after it drains, fill it with water again and see how long it takes to drain. If the hole drains within an hour you have good drainage. If the water has not drained out of the hole within one hour, the soil is poorly drained and you must correct the drainage problem before planting. Planting in raised beds is the best solution in heavy soils. Raised beds are built on top of the native soil to a depth of 12″ to 18″ and held in place with timbers or stones. Raised beds may require watering during the summer as they dry out quickly.

Aeration: Aeration is important for healthy growth of rhododendrons and azaleas. Beneficial microorganisms in soils require air for respiration and metabolism. Vital microbial and fugal activity, such as decomposition of organic matter that make nutrients available for plants, nitrification and beneficial mycorrhizal associations, depend on the oxygen present in soil. Poor aeration results in the development of toxins in soil. Plants in heavy soils with poor aeration often become chlorotic from malnutrition. To improve soil aeration the best amendment is organic matter, with compost being an excellent choice. Soil bacteria acting on compost produces humus that binds with soil particles – that forces tightly packed particles apart; improves drainage and allows the fine roots of rhododendrons to more easier penetrate through the soil. In coarse sandy soil, it lodges in the large pore spaces and acts as a sponge, so the soil stays moist longer. Amending heavy clay soils is not recommended. Eventually the organic amendments break down and the soil reverts to its original condition. As mentioned above, in gardens with heavy clay soil the best approach for growing rhododendrons and azaleas is using a raised bed atop the native soil.

Acidity: Rhododendrons and azaleas prefer acidic soils having a pH between 4.5 to 6.0. Rhododendrons and azaleas will let you know if the pH is not correct. If the leaves turn yellow between green veins then you most likely have a pH problem. If this occurs, a soil test is suggested for exact recommendations on adding a soil amendment to the soil in order to adjust the pH. Materials commonly used to lower soil pH are wettable sulfur or ferrous sulfate. Do not use aluminum sulfate to acidify the soil; it is toxic to rhododendron and azalea roots. Avoid planting azaleas near concrete sidewalks, driveways or foundations that may leach out lime which raises the pH. In rare cases, the pH may be too low. This is equally serious and must be rectified. The recommendation is usually to use dolomitic limestone.

Soil Mix: About half of the planting medium should be organic material. Combinations of sphagnum peat moss, pine or fir bark fines, compost, and aged, chopped leaves should be worked into the soil to a depth of about 12″. Oak leaves are excellent. Make sure there are no walnut tree roots or leaves in the soil. All parts of walnut trees are toxic to rhododendrons and azaleas. Pine bark is particularly good because substances in the pine bark are thought to inhibit fungi that cause root rot. Adding a large amount of organic matter will raise the bed, which will improve the drainage and aeration of the soil. Inorganic materials that may also be added to soil include perlite, vermiculite or small diameter lava rock. Time-tested mixes for growing rhododendrons and azaleas in raised beds include the following:
• Rhododendron Species Botanical Garden mix: two-thirds coarse sand mixed with one-third medium bark, no soil
• Everett Farwell rhododendron mix: 80% medium fir bark mixed with 20% small (⅛”-¼” diam.) crushed lava rock, no soil
• Holden Arboretum mix: five parts coarse sand and one part medium pine bark to four parts loamy soil.
Up to ¼ loamy soil can be added to ¾ RSBG or Farwell mixtures.

Keep Moist: Rhododendrons and azaleas will not survive in wet, poorly-drained soil. Although too much water can injure the roots it is important that they receive adequate moisture, especially during the first year after transplanting. A two to three inch layer of organic mulch surrounding the base of the plants helps retain moisture and helps control weeds.

More information about soils can be found in the following Journal ARS articles:
Tips For Beginners: Good Soil Promises Rhody Success by Harold Greer
Tips for Beginners: How To Adjust Acidity Levels in Your Soil by Fred C. Galle
Experiences With Rhododendrons In Southern Red Clay, More About Rhododendrons In Southern Red Clay by C.A. Dewey, Jr.

Index of Contents


Landscape Use

Plant Selection

What To
Plant Where





Pruning & Spent
Flower Removal

Propagation & Hybridizing


Insect & Disease Control

Growing & Choosing Rhododendrons & Azaleas

By Kenneth Cox, Glendoick


  • Rhododendrons need acid soil and they naturally grow on peaty soils in the Himalaya, Japan and China.
  • Soil acidity is measured according to the pH scale. Ideal is pH 4.5-6. Neutral is pH7 and higher than 7 alkaline.
  • Most soil in Scotland is naturally acidic.
  • Soil may have been artificially limed for farmland, growing vegetables etc. This washes out over 3-5 years. If liming has been done recently you can balance this by planting with peat. You can also use sulphate of ammonia to lower/acidify soil pH: apply before planting as too much can burn leaves.

How do I know if I have acid soil? Soil test kits are not always accurate: you may need to do several samples to get consistent results. If there are rhododendrons/ acid loving plants growing well nearby, your soil is acid. Best advice is to ask neighbouring gardeners.


  • Rhododendrons need an open soil mixture. Very heavy (clay) and very fine particles (silt) are not suitable.
  • To improve soil, making it more open (i.e containing air pockets) organic matter should be added: leafmould is the best. Alternatives are compost (own or bought), composted bark or conifer needles.
  • There is little point in spending money on rhododendrons and azalea if you are not prepared to do some soil preparation. Improve the soil in an area much bigger than the rootball so there is room to grow.
  • If drainage is good, then soil preparation need no more than 30cm (12in) deep.
  • Peat can be used to improve the soil but it is not neccessary if you have other substances to use. Peat is useful as it is sterile, acidic and helps hold moisture but it has little structure, no feed and no mulching value. Ericaceous compost which you can buy in garden centres is a mixture of peat, green waste and some fertiliser. For containers you are advised to add perlite to the mix to ensure good drainage.


In heavy clay soil, a raised bed is best: 30-45cm deep on top of the clay soil. Make a soil-compost-bark-peat etc mix and plant into this. Glendoick Garden Centre Pagoda garden is an example of heavy clay soil with raised beds created on top of it. Peat walls and raised beds in Glendoick Pagoda Garden


Rhododendrons must not be planted too deep. The rootball should be just below the surface. If you bury the rootball, you may kill the plant. Do not put very thick layers of mulch over the rootball.


Ensure plant is well-watered (but allowed to drain) before planting. Mix some organic matter (see above) into the existing soil as a planting medium. Soil should be firmed up around the roots but do not stamp on the rootball; avoid compacting the soil. For bare rooted stock, October to early April is the best planting time. Container stock can be planted at any time but if planted May-August water through the first growing season.


  • Rhododendrons dont grow flower well under greedy trees: tree roots will take most available moisture and lack of light creates straggly, shy-flowering plants.
  • The further north, the more light is required: in Cornwall you can grow in more shade than Scotland.
  • The worst trees are dense, greedy ones such as beech and sycamore. The roots of the tree will reach as far as the dripline (where the branches extend to). Ideally in summer you should see some sky overhead. If you can’t, you have a problem.
  • If you live in Scotland, ignore advice that advocate shade or part shade. Maximum light = maximum flowers.
  • Good trees to grow with rhododendrons: Japanese maples, flowering cherries, Sorbus, Crataegus (hawthorn), Eucryphia, conifers: pine, larch, spruce (Picea), firs (Abies), cedar. Plant dwarf rhododendrons and evergreen azaleas in full sun in Scotland. Deciduous azaleas, larger hybrids and species can take some shade.


Varieties with large leaves, early growth or which are on the tender side for your climate require shelter from wind, particularly from south westerlies and north easterlies. Options if shelter is poor:

  • Plant a shelter belt of vigorous trees and shrubs.
  • Use rokolene (spun plastic membrane) or similar material to help plants establish.
  • Plant hardy wind-tolerant rhododendron varieties on the windward side and less hardy varieties inside these.


Best choices for containers are dense, compact plants with good foliage. Those with unusual or coloured foliage are particularly good. Evergreen azaleas, yak & R. williamsianum hybrids are best choices for containers outdoors. Ensure good drainage as rhododendrons hate waterlogged containers. Use peat/ericaceous compost (with John Innes added if you can get it) and add some perlite, grit or bark. Ensure there are plenty of drainage holes and that they don’t get blocked.


Tender scented varieties can be grown in greenhouse/conservatory and brought in to house in flower. Rhododendrons dislike central heating and seldom succeed as house plants so need to be grown in a cool greenhouse; outdoors in summer. Ensure pots have good drainage and keep on the dry side. Feed and repot when plant becomes very pot-bound. Do not over pot as Maddenia and Vireyas like to be a bit pot-bound. Indica (indoor) azaleas good indoors, best put outside in Summer.

Growing Rhododendron: Caring For Rhododendrons In The Garden

The rhododendron bush is an attractive, blooming specimen in many landscapes and is fairly low maintenance when planted properly. Growing rhododendron successfully requires the proper planting spot for the rhododendron bush. Proper soil preparation is also necessary for the health of this acid loving plant.

Soil preparation is best accomplished in autumn before planting the rhododendron in spring. When to plant rhododendron will depend on the USDA zone in which it grows. Growing rhododendron is an exacting task, but with the right soil and location, the rhododendron bush will provide an optimum performance.

Unlike many blooming plants, rhododendron does not like full morning sun in winter and does best when planted in dappled shade on the north side of a building. Growing rhododendrons are happiest in a location protected from the wind and not under eves of a building.

When to Plant Rhododendron

Plant the rhododendron bush in spring when danger of frost has passed. Plant the bush high in properly prepared soil, as soggy and waterlogged roots are the main cause of plant failure in the landscape.

The rhododendron bush will likely be purchased as a containerized plant or a balled and burlapped specimen. The root ball should be soaked prior to planting. Moisture is required for proper rhododendron care. Place the plant in a tub or bucket for a brief soaking, until air bubbles disappear. Plant the rhododendron bush so that its crown is at the same level as in the pot.

Soil Preparation for Planting Rhododendrons

Correct soil pH for the growing rhododendron bush is crucial. Between 4.5 and 5.5 on the pH scale is appropriate. A soil test is the best way to determine the pH of the soil and make amendments. Aluminum sulfate should be avoided when amending beds for growing rhododendrons; agriculture sulfur is preferred, as the aluminum may be harmful to the growing rhododendron.

The rhododendron bush is best planted in groupings in prepared beds as opposed to individual planting holes. Caring for rhododendrons will be simpler if they are planted is moisture-retaining but well-draining, loamy fertile soil with the proper pH. A 50 percent ratio of organic matter is encouraged as a soil amendment, as it provides aeration and drainage and allows the rhododendron bush to set higher.

Caring for Rhododendrons

Once properly located in the planting bed, water thoroughly and cover with an organic mulch which will break down to supply nutrients as it decomposes. A pine bark covering applied at 2 inches (5 cm.) is thought to inhibit fungi that cause root rot. Do not mulch with peat moss, as it is difficult to rewet after it has dried out. Proper mulching will decrease the need for future rhododendron care.

Rhododendron care includes yearly fertilization which is best applied in fall, following a hard freeze or in early spring. Use fertilizer for acid-loving plants, such as organic cottonseed meal. The organic material you have worked into the soil previously will break down to provide some of the necessary nutrients.

Consistently moist soil is needed for proper rhododendron care, but too much water creates problems for the growing rhododendron. When leaves curl and twist, this indicates that water is needed immediately. The rhododendron bush should not be allowed to go through the stress of wilting. Shade-loving annuals, such as impatiens, may be planted as a companion to the rhododendron to indicate when water is needed.

Growing healthy and long-blooming rhododendrons starts with properly amended soil and planting in the correct location. These steps ensure minimal effort when caring for rhododendrons. Once sited properly, the rhododendron needs only adequate watering, pruning and deadheading of the flowers to encourage their abundant return.

Feeding Rhododendrons: When And How To Fertilize Rhododendrons

Fertilizing rhododendron bushes isn’t necessary if the shrubs are planted in fertile soil. If garden soil is poor, or you use certain types of mulch that deplete nitrogen in the soil, feeding rhododendrons is one way to provide the plants with nutrients. Read on to learn how to fertilize rhododendrons.

When to Feed a Rhododendron

If your soil is fertile and your plants look happy, there’s no urgency to learn about feeding rhododendrons. No fertilizer is always better than too much fertilizer so you might do best leaving healthy plants alone.

Be wary of nitrogen deficiencies, however, if you mulch with fresh sawdust or wood chips. As these materials disintegrate into the soil, they use up available nitrogen. If you see your rhododendron growth slowing and the leaves turning yellow, you’ll need to start fertilizing rhododendron bushes with a nitrogen fertilizer.

Take care when applying nitrogen fertilizer. If you live

in a cold climate, don’t add nitrogen after early summer since it can produce lush new growth easily damaged in winter. Apply only what you need and no more, since excess fertilizer burns a plant’s roots.

How to Fertilize Rhododendrons

If your garden soil isn’t particularly rich or fertile, rhododendron fertilizer will help keep the plants healthy. Generally, shrubs require three major nutrients to thrive, nitrogen (N), phosphorus (P) and potassium (K). Rhododendron fertilizer will have the proportions of these listed on its label in this order: N-P-K.

Unless you know that your soil is deficient in one nutrient but not the other two, choose a complete fertilizer containing all three ingredients, like one with “10-8-6” on the label. You may notice some fertilizers in the garden store specifically for azaleas and rhododendrons. These specialty fertilizers are formulated with ammonium sulfate to acidify the soil at the same time as providing nitrogen.

If your soil is naturally acid, no need to buy these expensive specialty products for feeding your rhodies. Just use a complete fertilizer should do the trick. Granular fertilizers are less expensive than other types. You just sprinkle the amount specified on the label on the top of the soil around each plant and water it in.

It’s easy to figure out when to feed a rhododendron. You can start fertilizing rhododendron bushes at planting time, and do it again in early spring as flower buds swell. Use a light hand, since applying too much rhododendron fertilizer can do more harm than good. Sprinkle on once again very lightly at leaf emergence if the new leaves look pale.

Proper fertilizing keeps azaleas and rhododendrons looking good all season

Question: When should you fertilize azaleas and rhododendrons? Is it better to do it in the spring or the fall? What happens if you fertilize in the winter?

Answer: Azaleas and rhododendrons are very common landscape plants here in Pennsylvania, probably due to their evergreen nature and beautiful flowers. They make terrific foundation plants, and when grown in the right conditions, they’re easy to care for.

In their native habitats, both azaleas and rhododendrons are understory shrubs, meaning they much prefer full to partial shade conditions, especially during the hot afternoon hours. They are not a good choice for areas of the landscape that receive full sun. When planted in full sun, azaleas and rhododendrons often suffer from infestations of an insect pest called lacebug. To grow the best azaleas and rhododendrons, site them properly.

Another thing these two plants have in common is their need for acidic soil. Azaleas and rhododendrons grow best in woodland areas with a soil pH between 4.5 and 5.5, so even when you’re growing them as a landscape plant, this pH requirement is necessary. If your soil’s pH is not optimal, these two plants will show it with leaves that turn yellow between their leaf veins (called interveinal chlorosis), slow growth, and reduced flowering.

Azaleas and rhododendrons, along with most other evergreens, require an acidic soil because an acidic pH level increases the availability of iron in the soil, a nutrient evergreen plants need a lot of to support their year-round foliage. Because of this, before fertilizing any azaleas and rhododendrons, I always recommend getting a soil test (available from the Penn State Extension Service; 724-837-1402 in Westmoreland County and 412-482-3476 in Allegheny County) to make sure the soil pH is optimum. The plants may not need to be fertilized; you may only need to adjust the pH to make them happy and healthy. Typically, elemental sulfur or ferrous sulfate is used to adjust the pH, but how much you’ll need to use is dependant on the existing pH of your soil.

If you test your soil and the pH is optimal, and you’re growing these plants in well-drained soil that’s high in organic matter, fertilization is seldom necessary. But, if soil test results come back informing you that your rhododendrons and azaleas do, in fact, need to be fertilized, choose an acid-specific granular fertilizer, such as HollyTone, to do the job.

Fertilization of these plants is best done in the early spring, just before they flower and enter a period of active growth.

Fertilizing in the late summer or autumn generates new, late-season growth that’s susceptible to damage from freezing winter temperatures because it does not have time to harden-off before frosts arrive.

Winter fertilization should be avoided as well. Since the plant is not in an active state of growth during the winter, most of the nutrients are likely to run off before they can be absorbed by the plant the following spring. It would likely be a waste of your money and time.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to [email protected] or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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    Paul Lawry from Nanaimo Chapter provides valuable guidelines for all gardeners. Listen to his counsel, take notes, and mark your own checklist below:

    Even though it may still be cold, damp and miserable outdoors, an occasional dose of sunshine could certainly put the gardening bug into you. With a little luck, Mother Nature will send a few blossoms your way this month. We are now at a time when we can no longer put off those garden projects, waiting for a nice day.

    • Don’t be caught off guard though, winter is far from being over! If exceptionally cold weather is forecast, provide protection to early flowering or tender plants by covering them with some type of cloth material. Remove the covering as soon as the weather moderates again.
    • Deciduous shrubs and trees are still dormant enough to transplant this month, once the buds have begun to swell, it will be too late.
    • Trees, which weren’t fed last fall, should be deep fed by punching a series of 1-2 in. Holes two feet apart around the drip line and filled with an appropriate food. A mulch of well-composted manure is also an excellent treat for your tree.
    • Fertilize shrubs and evergreens if this wasn’t done in February. Use an acid type rhododendron fertilizer to feed evergreens, conifers, broad leaf evergreens, rhododendrons, azaleas, and camellias. Use an all-purpose fertilizer to feed roses and other deciduous trees and shrubs. If you use dry type fertilizers, be sure to water it in thoroughly.
    • Prune your summer flowering shrubs NOW… but be aware that spring bloomers have already produced their buds last fall, and pruning them now will result in the loss of flowers. Forsythia, quince, spirea, and other early spring flowering shrubs should be pruned a little later, after they have finished flowering. Prune to improve the shape of the plant, as well as to open up the center of the plant to good air circulation and sun exposure. Always start your pruning by removing all dead, decayed or broken branches.
    • It’s a good time to stroll around and trim back any branches that were damaged by the ravages of winter.
    • If you haven’t yet applied your dormant fruit spray, DO IT NOW!
    • There often is a strong temptation to start removing winter mulches from your flowerbeds…WAIT! Pull the mulch off gradually as the plants show signs of new growth. Remember: the purpose of winter mulch is to act as a protector from sudden changes of temperature and chilling winds…so keep mind that it is still winter. Acclimatize your plants by removing the mulch over a periods of days, allowing the light and air to reach the new growth slowly. It is much better to remove the mulch a little later than to remove it too early.

    Paul comments further that most of us have other plants to enhance the beauty of rhododendrons, here are a few more things to think about…

    • Roses can be pruned now. Severe pruning results in nicer, long-stemmed flowers, and more compact bushiness. Begin to spray roses for black-spot. Feed roses.
    • Plant daylilies, bleeding hearts, and plantain lilies this month.
    • Deciduous vines such as honeysuckle should be pruned and shaped.
    • Divide and transplant summer blooming perennials and fertilize established ones as soon as new growth appears.
    • Check your stored plants such as fuchsias and geraniums, and if they are shriveled water them lightly.
    • Summer flowering bulbs may try to start into growth if they are subjected to heat. They should be kept very dry, and stored at 45 degrees F. If they are shriveling, put them into slightly damp peat moss, but keep them cool!
    • If you plan to grow lobelia, ageratum, verbena, petunia, vinca, or other plants from scratch, the seeds should be started indoors in the later part of the month.
    • Climbing roses should be thinned out to get rid of last years tangled growth.
    • Sow seeds of summer blooming annuals indoor. Seeds, which were started indoors last month, may be transplanted from the flats into peat pots and given dilute fertilizer.
    • Alternating thawing and freezing can tear plant roots and even force the plant right out of its hole. If you notice any plants that have heaved, push them back into the earth, push them back into the earth, and tamp lightly with your foot.
    • Remove all dead blooms from bulbs.
    • Fertilize any bulbs that have finished blooming with bone meal or bulb booster.

    Paul tosses in a few more added points not to forget…

    • The most dreaded task of all tasks is…weeding! BUT it is one that really needs to be accomplished before the weeds have a chance to flower and go to seed. Remember once the weeds go to seed…you can be fighting that weed seed for up to seven years…or more! An awful thought! Most weeds can simply be pulled or cultivated out of the garden while they are young.
    • Keep an eye out for aphids (spray off with water) and cutworms (cutworm dust).
    • Continue feeding our feathered friends, you’ll want them to stick around to help you in insect control when the weather warms again. AND, clean out all of your birdhouse NOW so that they will be ready when the birds return.
    • Did you check your garden tools yet? Don’t wait ’til the spring rush to get your mower back in shape!
    • In the event of snow, be sure to shake or brush off the white stuff from the branches of your evergreens and shrubs.
    • It’s time to turn the compost pile!

    Feeding And Pruning Azaleas And Rhododendrons

    Azaleas and Rhododendrons are among the most popular flowering shrubs and are commonly used in landscapes in many regions. Their spring beauty offers blossoms of white, pink, reds, lavenders, orange and purples, providing an array of color to any landscape.

    Typically these flowering shrubs are acid loving, meaning they prefer soils with a low pH level. This can be maintained by adding various acidifiers, such as HiYield Aluminum Sulphate, to the soil’s surface annually.

    The fertilizing of Azaleas and Rhododendrons should be performed shortly after their flowering period has ended. Just apply a granular fertilizer to the soil’s, or mulch layer’s, surface. We suggest using Fertilome Azalea, Rhododendron, Camellia Food which should to be applied every 4-6 weeks during the growing season between flowering in spring and bud set in early fall. Liquid fertilizers can be applied as a supplement, but we highly suggest a slow release granular-based fertilizer for outdoor shrubs.

    Pruning these beauties is often misunderstood and should be also performed shortly after the flowering period has ended. Azaleas, which react well to pruning, can be hand-pruned or sheared by removing all leggy or irregular growth for shaping and size control. Rhododendrons, if maintained yearly, can be taken care of by pruning or pinching the new growth shoot from the branch tips, or often around the spent blossom. With heavy pruning the new shoot growth will push inner growth buds deeper within the shrub or behind the blossom. However, lighter tipping on the new growth will simply terminate and create branching from beneath the cut.

    If your Rhododendrons are allowed to get too large, heavier pruning can be done. Simply go further behind the blossom, which will appear to be a woodier stem appearance. This, however, is just fine and new growth buds will slowly begin to develop lower behind the cuts along the stem.

    Just another quick tip for extra advice to make these beauties thrive: apply Fertilome Liquid Iron to the soil area beneath these flowering shrubs at least once yearly, preferably in mid-spring following pruning. This will create larger, darker green, and lush foliage for an even more spectacular appearance.

    Azalea Mulching Guidelines: What’s The Best Azalea Mulch

    Image by Hiro_photo_H

    Azaleas, plants in the Rhododendron genus, are among the most colorful and easy-care flowering shrubs a gardener can have in the backyard. Their requirements are few, but they do need moist soil. Mulching azalea bushes is one way to keep the humidity in the soil, but using mulch for azaleas helps the plants in other ways too. Read on for information about the best azalea mulch, including tips on how to mulch azaleas.

    About Azalea Mulching

    Before you choose a mulch for azaleas, it’s important to understand the concept of mulch. Mulch is a verb that means placing a layer of material on the top of the soil around plants to hold in moisture and keep down weeds. It’s also a noun referring to the material you can use.

    Almost anything capable of being layered can work as mulch, including newspaper, pebbles and chopped dry leaves. But many gardeners think organic mulch is best, and it does seem to be best for azalea mulching.

    href=”https://www.gardeningknowhow.com/garden-how-to/mulch/best-mulch-for-garden.htm”>Organic mulches are materials that were once alive, like pine needles, organic compost and dried leaves. Organic mulches work best as mulch for azaleas since they disintegrate into the soil over time, enriching it and increasing drainage.

    Reasons for Mulching Azalea Bushes

    Azaleas can grow into good-sized shrubs, with some cultivars shooting up taller than the average gardener. But no matter how tall they grow, their roots are quite shallow. These plants need slightly acidic soil with excellent drainage, since they don’t like wet feet. Still, azaleas only thrive if the soil around their roots is moist soil.

    That’s where mulching azalea bushes comes into the picture. Azalea mulching means you can water less but offer your plants consistently moist soil, since the best azalea mulches prevent moisture from evaporating in heat.

    How to Mulch Azaleas

    If you are wondering how to mulch azaleas, you’ll be happy to learn that it’s an easy task. You’ll need a good, organic mulch.

    The best azalea mulches include pine needles and dried chopped oak leaves. These are organic mulches that do the job keeping the moisture in the soil, regulating soil temperature and keeping down the weeds. They also add a little acidity to the soil.

    Mulching azaleas involves mounding about three or four inches (7 to 10 cm.) of one of these mulches in a wide circle around the base of the plant, covering the root area. Don’t extend the mulch right up to the plant; keep the mulch a few inches from the stems and foliage.

    It’s best to mulch soil that is already moist. You can do this by waiting until after a rain or watering the soil before mulching. Keep your eye on how the mulch is doing and replace it when it breaks down, usually at least once or twice a year.

    What Rhododendrons Require

    Rhododendron Basics by Harold Greer

    from Greer’s Guidebook to Available Rhododendrons:
    Requirements Diseases Non-Disease Problems Insects Pruning Deadheading Propagation


    Rhododendrons are forgiving plants, but there are some things they just won’t tolerate. So, it is important to understand their basic requirements.

    First: Rhododendrons must have a constant supply of moisture. You may occasionally see a rhododendron that will survive without being watered, but it does so only under protest.

    Second: Rhododendrons must never sit in stagnant water. Roots submerged in poorly oxygenated water will likely die, though a plant may survive through better drained surface roots. Hot, wet conditions are more dangerous than cool, wet conditions. That is why a rhododendron will survive in a wet spot in the Northwest during heavy winter rains but would not survive in a wet spot in the Southeast’s heavy summer rains.

    Third: Rhododendrons must be grown in an acid medium (pH 5-6) that is coarse enough for the roots to have access to needed oxygen.

    Understand and provide these three conditions and you will succeed wherever you live. These requirements aren’t difficult to provide once you understand rhododendrons’ needs relative to your specific soil and climatic conditions.

    Next, logically, you will ask: “How can I provide these three basic needs?”

    Consider the growing medium and include in your thinking the soil and drainage that is underneath the proposed planting. You must determine whether or not your soil has good drainage. If heavy clay is present you must overcome this barrier. Dig a small hole and run some water into it; if the water does not disappear in a very few minutes, you have poor drainage. This is not a sure test, but it will give you a good indication. Now, examine the soil texture: Is it sandy, or is it composed of fine clay particles? Sometimes the topmost soil layer will drain well, but there will be hardpan underneath it that will not drain. So, watch for this condition.

    Now let’s talk about the actual planting medium to use. We’ll come back to natural soil later. There are a multitude of mediums available and almost any one of them, given the proper amounts of water and fertilizer, will produce healthy plants.

    Something is needed that will provide adequate air spaces in the soil, and the slower this material decomposes the better. Second, something is needed that will hold a certain amount of water so that the plant does not dry out too rapidly. Barks are generally quite good, as they usually contain both fine and rough textured materials. However, the much heavier, coarser bark rock will not work well for this purpose although it will work as a mulch. Since they are on the outside of the tree, constantly exposed to the weather, nature has endowed barks with a sort of natural preservative which slows their hreak-down and inhibits many root-rot fungi. The breaking down process of organic material requires nitrogen; consequently, the faster it breaks down, the more nitrogen it uses.

    Sawdust often breaks down very fast and, therefore, requires a lot of nitrogen. Some types tend to hold too much free water and can cause conditions that are too wet. This is particularly true in hot, wet summer areas and probably contributes to the myth that sawdust will kill a rhododendron. Leaves and needles of most kinds of trees are okay, although some kinds do breakdown rather fast and can be a hiding place for insects and diseases. Nut shells, spent hops, corn husks and a multitude of other things will work well as long as they are not alkaline and do not have toxic materials in them. If you do not know whether or not the material has been used with rhododendrons, try a small quantity for a time before going all out. While it is unlikely that anyone has ever used them, even ground-up rubber tires would provide air space in the soil and achieve the same purpose as many organic materials.

    For the finer water-holding part of the growing medium, the choice is often peat moss. In some areas good local peat moss is available, but in recent years good peat moss has been difficult to obtain and often the powder that is sold as peat moss is worse than none at all. This is particularly true if you use only this very fine peat moss to mix with clay soil. The result will be a soppy soil that has no ability to hold air. Try to obtain the coarse nursery grind.

    Now mix the actual medium (soil) in which you are going to plant your rhododendron. The old formula of one-third sawdust or bark, one-third peat moss, and one third garden loam is all right, providing the humus material (sawdust, etc.) is coarse enough to supply the necessary amount of air in the soil. Up to one-third of the soil volume should be air space, so use common sense to provide a mix that will give you this result.

    Shows plant in simple raised bed (left side of drawing),
    or raised bed with retaining wall (right side of drawing)

    Almost any combination will work as long as it provides the necessary air. Remember: The slower the humus breaks down the better, because the longer those particles of humus are there, the longer the soil is going to contain a lot of needed oxygen. And, remember that organic material which breaks down too rapidly consumes lots of oxygen, which is going to have to be replaced.

    We now have the planting medium figured out, so let’s deal with the native soil. We have already determined how to tell if drainage is good or bad. If it is good, you can mix the planting medium into the top six to ten inches of soil and you are ready to plant. We are also assuming that the native soil is acid; if it is not, no matter how good the drainage, you are probably going to have to make a raised bed. If drainage is poor (and this true in many locations), you will need to plant nearly on top of the native soil. The illustrations will help show proper planting procedure.

    You may plant in a hole as this drawing shows if you have well drained soil. In poorly drained soil, if you dig a hole like this and fill it back with light soil, you may be creating a bucket which will hold stagnant water and kill your plant.

    Mulching is also important. The reasons for mulching are to keep the roots cool in the summer and protect them from sudden soil temperature changes in winter, to prevent drying out and to help keep the weeds down. In their natural environment rhododendrons have a mulch provided from their own leaves and those of the trees around them. The same is true of old plants in the garden; they provide their own mulch from the leaves they drop each year, so don’t be over anxious to rake out all of the fallen leaves. However, be aware that they are an excellent hiding place for pests and diseases. As to what to use as a mulch, just about any of those things which were stated earlier as good for providing air in the planting medium will also work as a mulch. You may plant in a hole as this drawing shows if you have well drained soil. In poorly drained soil, if you dig a hole like this and fill it back with light soil, you may be creating a bucket which will hold stagnant water and kill your plant. Be inventive, almost every area has some kind of waste product that can used for this purpose. Note: Do not use fine peat moss alone as a mulch; it will dry out and shed water like a thatched roof. Similarly, the use of black plastic is a bad substitute for proper mulching.

    When a rhododendron is newly planted, the roots are only in the existing ball and have not had time to grow out into the surrounding soil. If the ball gets dry, water will not easily be reabsorbed into the ball from the moist adjoining soil. Since no roots have had time to grow into the new soil, they can be dry even though it is sitting in damp soil.

    We now have the rhododendron planted in a good soil mix; it is well drained and we have mulched the plant properly. The final thing that we must do to be sure that our plant grows well is to water it sufficiently. The method of watering makes little difference and depends on your geographic location and the amount of water available. Drip irrigation is fine and uses the least water. Overhead watering is also good and can be used to advantage to cool the plants and provide lost moisture on a hot day. Don’t worry about the old tale that says you can’t turn on sprinklers over a plant in the sun; it won’t hurt, although once in a great while, you might get a small spot of burn on a leaf due to the magnifying glass effect of a bead of water. When a rhododendron is newly planted, the roots are only in the existing ball and have not had time to grow out into the surrounding soil. If the ball gets dry, water will not easily be reabsorbed into the ball from the moist adjoining soil. Since no roots have had time to grow into the new soil,
    they can be dry even though it is sitting in damp soil. It will actually do much good providing moisture that the plant is not able to bring up fast enough through its own roots. Many commercial rhododendron growers now have watering systems that turn on and off automatically during hot weather for this very reason, enabling them to grow plants in full sun that would otherwise burn badly. However, it is true that during flowering, overhead watering may damage the flowers. Also, in wet climates (particularly hot areas), if the foliage never dries out during the day, you may have more trouble with fungus disease.

    The main thing that we must make sure of is that the plant is getting wet. Quite often a plant will get completely dry and then no matter how much water you apply, the rootbal will just keep shedding it. The top of the soil may seem wet, and the soil around the plant may even be very wet, but the actual root ball of the plant is bone dry. This is especially true for newly planted rhododendrons, and it is the major reason for failure, or at least less than great success with that new plant. It is hard to believe that a plant can be within mere inches of a sprinkler that has been runnung for hours and still be dry, yet it can be SO TRUE!

    Rhododendrons do require adequate nutrients to grow and flower at their best, and these nutrients are usually provided from some form of fertilizer. Whether you use organic or “chemical” is your choice. Applied in proper amounts, either type will produce healthy plants. A properly fed plant is hardier and will withstand more cold than one that is under-fed. Research done by Dr. Robert Ticknor of Oregon State University indicates that more nitrogen is needed than what was once thought. He now recommends a 10-6-4 (nitrogen, phosphate, potash) formula. While phosphate does promote bud set, apparently the plant can only use a certain amount. Unlike nitrogen, phosphate and potash do not disappear from the soil, but build up little by little with successive fertilizing. Therefore, the old high phosphate formulas do not provide extra help to the plant. For the best growth and flowers on young plants in areas where the soil is not frozen all winter, apply fertilizer after the plant goes dormant sometime between late November and January, a second time in February/March, a third time in April/May and a final time in June/July. For most garden situations the old rule of “once before they bloom” and “once after they bloom” is still a sensible approach. Actually the fertilizer timing has nothing to do with the time the plant flowers, it simply means once in the early spring, probably March/April and a second fertilization about June/July. This timing will vary, depending on your climate, and is not critical.

    Rhododendron Basics by Harold Greer from Greer’s Guidebook to Available Rhododendrons:
    Requirements Diseases Non-Disease Problems Insects Pruning Deadheading Propagation

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