- Good Azalea Care: Azaleas, Noteworthy Shrubs For Any Garden
- How to Grow and Care for Azaleas
- How to Grow Azaleas Outdoors
- How to Grow and Care for Azaleas
- Selecting Your Azalea Varieties
- Care Of Indoor Azaleas: Tips For Growing An Azalea Houseplant
- Tips for Growing an Azalea Houseplant
- Care of Indoor Azalea
- Getting Greenhouse Azaleas to Rebloom
- Gardening : Keys to Planting Successful Azaleas : Flowers: Depending on varieties planted and location, they can produce brilliant blooms from October through June.
- Azaleas Made Simple
- Azalea Care
Good Azalea Care: Azaleas, Noteworthy Shrubs For Any Garden
Nothing is more beautiful than an azalea shrub in spring bloom. These easy-care shrubs come in so many colors it’s hard to find one that doesn’t suit your needs. Azaleas can be grown in nearly any garden, instantly adding interest and color to drab areas.
How to Grow and Care for Azaleas
Growing and caring for these shrubs is easy. That being said, there are some things to consider when adding them to the landscape.
Proper Azalea Care
To keep azaleas looking healthy, it is essential that you choose an appropriate planting location and practice proper azalea care. Azaleas actually look the most attractive when they are planted alone; however, mass plantings work well in larger areas, such as wooded sites.
Since the flower coverage on azaleas encompasses the entire shrub, placing them in a background of conifers, such as pines, or other acid-loving plants will help set off their colors while minimizing their heavy effect.
These shrubs should be planted in the spring, preferably within cool, lightly shaded sites. Full sun, especially in southernmost climates, can actually burn the leaves while heavy shade can deprive them of necessary oxygen, resulting in poor blooming and weaker growth.
Best Soil for Azalea Plants
Azaleas have shallow roots and require a well-drained, acidic soil. In poorly drained areas, azaleas should be placed in raised beds. Azaleas can also make exceptional candidates for containers.
It also helps to amend the soil with compost beforehand. To help conserve water, maintain soil temperature, and discourage weeds, mulch these shrubs with pine straw or composted pine barks and replenish annually. Organic matter added to the soil and an adequate layering of mulch will generally provide azaleas with sufficient nutrients; therefore, frequent fertilizing is often not required.
However, if there are low amounts of nitrogen in the soil, applying fertilizer may be necessary in order to prevent a nutrient deficiency. Symptoms of deficiency in azaleas include stunted growth, smaller greenish-yellow leaves, or early leaf drop. Fertilizing of these shrubs should take place in late spring to early fall.
Common Azalea Diseases & Pests
Although azaleas are generally free of pests and diseases with proper azalea care, common azalea diseases and problems do exist.
Insects that can affect azaleas include lace bugs and spider mites. Lace bugs are more likely to target shrubs that are grown in areas of full sun.
Petal blight, leaf spots, and root rot are common diseases associated with these deciduous shrubs. Placing azaleas in areas with good drainage and conserving water by applying mulch usually helps reduce the chances of plant damage due to these problems.
How to Trim Azaleas
To maintain a more compact appearance or simply to encourage bushier growth, trim azaleas after their blooming period has expired. Taking time to trim azaleas by cutting back the branches of these shrubs will also help renew overgrown plants.
Keeping your azaleas healthy throughout the growing season with good azalea care will ensure an abundance of beautiful blooms for many springs to come.
How to Grow Azaleas Outdoors
Azalea image by fabiomarc from Fotolia.com
The azalea is a member of the heath family, in the genus Rhododendron, and a relative of the blueberry. It is a flowering shrub that is popular in the home landscape for its ability to tolerate shade and to bloom in shades of red, pink, purple and white. There are early, mid-season and late blooming azaleas. With careful planning, you can have an azalea garden in bloom for at least eight months of the year, according to Master Gardeners at the University of Georgia extension. Plant the azalea in an area that will keep it out of direct sun and protected from winds. The azalea is hardy to various USDA zones, depending upon the variety.
Obtain a soil pH test. Although you can purchase a home testing kit at most gardening centers, your county cooperative extension office provides testing and the agent can give you recommendations on materials needed to raise or lower your soil pH. Azalea requires a soil pH of 5.5.
Prepare the planting area by adding a three-inch layer of compost or well-rotted manure to the soil and mixing it to a depth of eight inches. Add soil amendments to adjust the pH as needed. Mix them into the soil to the same depth.
Dig a hole that is the same depth as the pot that the azalea is growing in. Make it three times the width. Remove the azalea from the pot. If the roots are tangled, gently loosen them with your fingers. Place the root ball in the bottom of the planting hole, fill the hole with soil and use your feet to pack the soil around the base of the plant.
Pour a three-inch layer of mulch on the soil at the base of the azalea. Keeping it two inches from the plant, spread it out to the same width as the azalea, completely encircling the plant.
Water until you see the water puddle. Keep the soil moist until the plant is established, which will be evidenced by new growth. After that, water when the top two inches of soil are dry.
Replace the mulch around the azalea every spring with a fresh layer. Pine needle mulch is preferable as it will help to maintain the soil’s acidity.
Prune the azalea in early spring. Growers with the Azalea Society of America suggest that you prune in stages to minimize the shock to the plant. Cut out all dead wood and then remove two or three tall branches. Cut them back to a branch that is growing in the direction in which you want the plant to grow. The following year remove three more branches and repeat the procedure in the third year.
How to Grow and Care for Azaleas
When azaleas burst into bloom, it’s hard to resist the urge to add one or more to your landscape. Despite a reputation for being finicky, these spectacular shrubs are easy to grow once you understand their basics needs. By choosing the right azaleas for your home and caring for them properly, you can grow gorgeous azaleas of your very own.
- Selecting Your Azalea Varieties
- Providing Azaleas With Proper Soil
- Watering Your Azaleas Properly
- Feeding Your Azaleas the Best Fertilizer
Selecting Your Azalea Varieties
Thanks to modern plant breeders, azaleas aren’t just for southern and coastal gardeners any more. Gardeners across the United States can enjoy beautiful azaleas by selecting the right plants from the start. In choosing the best azaleas for your garden, keep the following considerations in mind:
- Growing zone. Flower buds on spring-blooming azaleas form long before winter. Choosing types that withstand your winter temperatures is essential to spring blooms. Many azaleas are only bud-hardy in the country’s southern half, but some northern-bred types can withstand minus 45 degrees Fahrenheit.1 Your county extension agent can help with zone information and tips on plants that will thrive.
- Light conditions. Azaleas are often considered shade plants, but many varieties tolerate direct sun — and some even require it. In northern climates, where sun is less intense, azaleas often prefer more sun. Choose azaleas that fit your garden’s light conditions to help ensure attractive leaves and plentiful blooms.
mature size. Some azaleas, including native types, reach towering heights of 20 feet or more.2 But home gardeners have many smaller options. Dwarf azaleas grow 2 to 3 feet tall, and many garden azaleas stay 4 to 6 feet in height. Select azaleas based on mature height and width, not their size when you buy them.
- Bloom time. Azaleas are famous for springtime beauty, but they come in early, mid- or late-flowering varieties. Reblooming types flower in spring and again in fall. Extend the show for months by growing azaleas with staggered bloom times.
- Flower color and form. Azalea flowers offer something for everyone in their broad color range and flower forms from thin, spider-like petals to full, ruffled blooms. Eliminate surprises, and buy azaleas when they’re blooming so you exactly how flowers will look.
- Leaf retention. Some azaleas are “evergreen” and keep their leaves year-round, but others are “deciduous,” meaning they naturally drop their leaves in fall. Know what to expect from the type you choose, so you can respond appropriately if leaves drop.
Care Of Indoor Azaleas: Tips For Growing An Azalea Houseplant
Greenhouse azaleas are those beautiful, multicolored joys of spring, those bright spots in the grocery store or garden nursery when everything else is winter gray. Their bright beauty has caused many a gardener (and many non-gardeners) to ask, “Can you grow azalea indoors successfully?” The answer is, “Of course you can!”
Tips for Growing an Azalea Houseplant
You can grow azalea indoors much like any other houseplant, but as with other blooming plants, there are a few tricks you need to know about the care of indoor azalea if you want to keep them blooming year after year.
The first step in growing an azalea houseplant is to choose the right shrub. You are looking for greenhouse azaleas, not hardy azaleas, which are only grown outdoors. Both are Rhododendrons, but different sub genres, one of which is only hardy to USDA plant hardiness zone 10. That’s the one you want.
Greenhouse azaleas aren’t always marked as such, but they will almost always be sold indoors and usually come with that decorative foil wrapping around their pots. Look for a plant with only a few buds open and showing color. That way, you’ll be able to enjoy that first full bloom for a longer period of time.
Flower buds should look healthy and be at different stages of development as a sign they are actively growing. An azalea houseplant with yellowed leaves isn’t healthy. Look under the leaves as well. That’s where those pesky whiteflies and mealybugs dwell. They love azaleas.
As houseplants, many growers ship azaleas in clear plastic sleeves. These sleeves are meant to protect the plant in shipping, but they also trap the ethylene gas released by the plant, which can cause leaf drop. Try to find a retailer who removes them or, if you can’t, remove it from your greenhouse azalea as soon as you get it home.
Care of Indoor Azalea
In their natural environment, these plants live in the understory of high trees. They thrive in cool, filtered sun. Azaleas as houseplants do best at cooler temperatures, ideally around 60-65 F. (16-18 C.). Cooler temperatures will also help the blooms last longer. Keep them well lit, but out of direct sun.
Moisture should be your greatest concern in the care of indoor azaleas. Never allow your plant to dry out. While watering from the top may provide sufficient care, indoor azaleas enjoy the occasional dunk, pot and all, in a larger container of water. When the bubbles stop, pull it out, and let it drain. Whatever you do, don’t let these plants dry out. Keep them damp, not soggy, and don’t fertilize until flowering is complete.
At this point, the lives of most azaleas as houseplants are over, because this is where most people throw them away or plant them in the spring garden for their foliage, allowing Mother Nature to do the deed with frost the following fall.
Getting Greenhouse Azaleas to Rebloom
Can you grow azalea indoors and get it to rebloom? Yes. It isn’t easy, but it’s worth a try. Once the blooms have faded, give your plant a little more light and fertilize it with an all-purpose liquid fertilizer every two weeks. When the weather warms, plant it pot and all in your outdoor garden or keep the pot in a semi-shaded area indoors or out. Since they prefer slightly acidic soil, you may want to use a fertilizer manufactured for that purpose.
Shape the plant in midsummer, cutting back any straggly growth and keep it well watered. Bring it back indoors before the first frost of autumn. Now the hard part begins. Between early November and early January, greenhouse azaleas need temperatures ranging between 40 and 50 F. (4-10 C.). A sunny, enclosed, but unheated porch will do the job so long as the temperature doesn’t drop to freezing. This is essential for growing an azalea as a houseplant, because the blooms set during this chilling time.
Give your plant enough water to keep it from wilting, but don’t be too generous and don’t fertilize. All the nutrition it needs has been stored in the leaves and fertilizing now will give you lush growth without flowers. In January, move the plant indoors, but it should still have nighttime temperatures around 60 F. (16 C.). That back bedroom that everyone complains about is ideal for this. In a few weeks, flowering should begin.
Growing and azalea houseplant and getting it to bloom again takes time and careful planning, but the reward of such lovely blooms make the effort well worth it.
Gardening : Keys to Planting Successful Azaleas : Flowers: Depending on varieties planted and location, they can produce brilliant blooms from October through June.
Right now is peak azalea season, when nurseries offer the best selection of plants, bursting with brilliant bouquets of colorful blooms.
Azaleas are one of the few plants that provide showy color all winter long, can be grown in sun or shade, and never need replacing–at least they shouldn’t.
For many people, however, azaleas seem difficult to grow and easy to kill. Most often, the problem is associated with over-watering and poorly drained soil. The key to growing beautiful azaleas is proper planting and watering.
It is also important to choose the appropriate variety for each particular location with regard to sun exposure and climate. With careful selection of early-, mid- and late-blooming varieties you can have azaleas blooming in your yard nine months out of the year, October through June.
Azaleas like to be kept moist, but not soggy. Always water deeply when you do water. This will help prevent brown leaf tips caused by salts in the water. Water only when the top of the soil begins to dry out.
In cool, shady locations this may be only two or three times a month, depending on the weather. During the summer, in hot, sunny areas, you may need to water every three or four days. When in doubt, don’t water–azaleas can tolerate dry soil much better than soggy soil.
Azaleas must be planted in well-drained soil. If your azalea looks like someone took a blow torch to it, most likely it is planted in heavy, hard or clay soil, which drains slowly.
The appearance of an over-watered azalea is often deceiving because the plant often appears drier than normal and the leaves may turn brown. You naturally assume the poor thing needs more water, and you water it even more.
The fungus Phytophthora occurs in soggy soils and is responsible for a significant percentage of azalea casualties. The plant first exhibits poor vigor, then begins to look dry, leaves turn brownish-green and there is no new growth.
Other soil inhabiting fungi, commonly associated with poorly drained soils, cause root rot and affect the plant by causing young leaves to yellow and wilt. Small leaves and reduced vigor also occur from root rot.
To prevent fungus diseases and problems associated with over-watering, proper planting is essential. Here’s how to plant:
Dig a hole at least twice as wide and one foot deeper than the container the plant comes in. Mix plenty of peat moss with some of the soil from the hole. Milfeld’s wholesale azalea nursery in Riverside, known for its beautiful, top-quality azaleas, recommends planting in 80% coarse peat moss and 20% good, light soil.
The peat moss helps provide an acidic soil environment that azaleas love. If your soil is clay or hard you will be planting in almost straight peat moss, using only about 10% of the soil from the hole, mixed together with the peat moss.
Place the plant so that it is 1 to 1 1/2 inches above ground level. Fill in with the peat and soil mixture and water thoroughly. Avoid stepping on the soil to tamp it down. This causes compaction and reduces the great drainage and aeration you just worked so hard to create.
Many azaleas can be grown in full sun. Milfeld’s nursery recommends Southern Indica varieties for full sun, and Belgian Indica, Kurume and Rutherfordiana varieties for shade. Make sure you get the right plant for the right location.
All azaleas are classified as early-, mid- or late-blooming varieties. According to Milfeld, early season sun-types bloom January-March, early season shade-types bloom October-February, mid-season sun-types bloom March-April, mid-season shade-types bloom February-April and late season sun and shade-types bloom April-May.
Satsuki varieties bloom May-June. Two spectacular red sun azaleas, classified as early to late bloomers, are ‘Red Wing’ and ‘Red Bird.’ They bloom seven to eight months of the year, prolifically at times, and at least spot blooms the rest of the time.
‘Alaska’ is another exceptional variety, a long-blooming, white, early- to mid-season shade azalea. ‘Fielders White,’ a mid-season sun azalea, is another outstanding white.
Azaleas are slow growers and light feeders. Fertilize three or four times a year during the spring and summer months, using Miracid or any good azalea acid fertilizer. Leaves that turn yellow with the veins remaining green indicate an iron deficiency (iron chlorosis)–treat with iron chelate.
Azaleas are relatively pest-free, but occasionally fall prey to spider mites. Silvery leaves, with webbing beginning on the undersides of the leaves and later covering the entire leaf, indicate their presence.
Bud mites are another type of mite that sometimes attacks azaleas, causing curled and distorted new foliage. For both types of mites spray with Cygon, Diazinon or Mavrik, according to label directions.
Azaleas Made Simple
‘George Lindley Taber’, a Southern Indica Hybrid. Van Chaplin
Azaleas prefer light shade and acid soil containing plenty of organic matter. This one is ‘George Lindley Taber,’ a Southern Indica Hybrid.
Azaleas are the one group of plants Southerners never tire of learning about. Here are answers to some basic questions readers ask about these popular shrubs.
Do azaleas need shade or sun?
Actually, they like a little of both but not too much of either. Plant them in blazing hot sun, and they may suffer leaf scorch or become targets for leaf-sucking pests such as spider mites and lace bugs. Plant them in dense shade, and they won’t bloom. A good location is where they receive either dappled sun all day or sun in the morning and light shade in the afternoon.
What kind of soil do they like?
Azaleas do well in moist, acid (pH 5.5 or so), well-drained soil with lots of organic matter, such as peat, compost, chopped leaves, or ground bark. They won’t grow in heavy clay, pure sand, or alkaline soil. If your existing soil is too bad to fix, plant azaleas in raised beds or containers.
How and when should I fertilize them?
Azaleas growing in acid, nutrient-rich soil don’t need much fertilizer. But if your soil is so-so or you notice the leaves turning yellow between the veins, feed them with a slow-release, acid-forming azalea fertilizer that contains iron and sulfur, such as Holly-Tone 4-6-4 or Scotts Evergreen, Flowering Tree & Shrub Food 11-7-7. Apply right after plants finish blooming in spring and again in midsummer at the rate specified on the label. If your azaleas need an immediate pick-me-up, switch to Miracle-Gro Azalea, Camellia, Rhododendron Plant Food 30-10-10. Both roots and leaves quickly absorb this liquid fertilizer, but you’ll have to apply it more often than the others.
How and when should I prune them?
Do so immediately after the plants stop flowering in spring. If you wait until summer, you’ll remove most of next year’s flowers. Use hand pruners, not hedge trimmers. Cut back to a branch or bud, and don’t leave big stubs.
How big will azaleas get?
That depends on the type. Low, spreading Satsuki Hybrids, such as ‘Gumpo,’ grow only a few feet tall. The popular Kurume Hybrids, including ‘Coral Bells’ and ‘Hershey’s Red,’ form dense shrubs 3 to 4 feet tall and wide. Southern Indica Hybrids, such as ‘George Lindley Taber,’ ‘Formosa,’ and ‘Pride of Mobile,’ can grow 8 feet tall and wide. Don’t plant these big guys under low windows.
When is the best time to plant azaleas?
Spring and fall, when temperatures are cool, are excellent times. But if you buy in spring when the azaleas are blooming, you’ll be assured of getting the colors you want. Summer planting is okay, but you’ll have to water frequently during hot weather.
Can I plant one of every color together?
Hey, it’s a free country, but we’d rather you didn’t. You’ll get a much better show by planting a mass of a single hue.
Azaleas are Southern signature plants in South Carolina landscapes. Numerous azalea species, hybrids and cultivars, either native to this area or hailing from the Orient, can be grown here, with bloom times ranging from early spring to midsummer. The numerous cultivars of the Encore™ series of azaleas offer blooms twice a year, in the spring and again in the fall. Azaleas are classified in the genus Rhododendron.
The ‘Formosa’ Southern Indica Azalea produces large blooms.
Joey Williamson, ©2013 HGIC, Clemson Extension
In order for azaleas to have healthy, vigorous growth, it is important to understand the impact of cultural and environmental factors on this plant. Choosing the proper planting location and using good planting methods and cultural practices are critical in providing the best conditions for optimum plant growth. For more information on the beginning steps to a healthy azalea, refer to HGIC 1058, Azalea Planting.
Azaleas prefer cool, partially shaded sites, such as the filtered shade of pine trees. Azaleas planted beneath hardwoods with shallower roots must compete with these trees for nutrients and water. If placed in the right location, however, they can do well on these sites. Although some varieties tolerate sun better than others, they all prefer an area that is not exposed to long periods of hot full sun and drying winds. Flowers last longer when plants are partially shaded. Azaleas exposed to full sun are more susceptible to lace bugs. Early morning sun exposure after a hard freeze may cause cold injury. Do not plant azaleas in heavy shade as poor flowering and weak growth result.
Azaleas are shallow-rooted plants that are easily damaged by excessive soil moisture. They grow best in acid (4.5 to 6.0 pH), well-drained, organic soils. Before planting, have the soil tested and adjust the pH according to soil test results.
Azaleas located in poorly drained sites do not receive the oxygen required for healthy growth and often develop root rot diseases. When planting in poorly drained areas, add composted pine bark to as large an area as possible, and plant the root ball higher than ground level.
A 2- to 3-inch layer of organic mulch is very important. It conserves soil moisture, maintains soil temperature and helps discourage weeds. There are many materials available suitable for mulching. Pine straw, composted pine bark and leaves work very well, enriching the soil with organic matter as they decompose. Keep the mulch a couple of inches away from the main stem to keep the bark dry and extend it beyond the outermost branches.
Azaleas are shallow-rooted plants and require irrigation during dry periods. This is especially true of those planted in the spring. Azaleas planted in warm weather in sandy soils may require watering of the root mass twice a week during the first year.
To determine when to water, pull back a small area of mulch near the base of the plant and check the moisture level of the root ball and surrounding soil. If the top few inches of soil feels dry, wet the soil deeply, to at least a depth of 6 to 8 inches.
Use soaker hoses or drip irrigation to slowly water the base of the plants. Overhead irrigation may promote disease.
Azaleas in waterlogged soils will decline and are susceptible to root rot diseases. It is important to reach a balance of regular, deep watering and good drainage to promote a healthy plant.
Azaleas have low nutritional requirements compared to other shrubs. A soil amended with organic matter prior to planting followed by a mulch of compost, shredded leaves, pine straw or other organic material will usually provide sufficient nutrients for adequate growth.
Before fertilizing, have a specific reason for doing so, such as increasing growth rate or correcting a nutrient deficiency. A nutrient deficiency can be exhibited by a number of symptoms including stunted growth, smaller than normal leaves, light green to yellowish leaf color and early leaf drop. Be aware that these same symptoms can be caused by other problems such as heavily compacted soil; stresses from insects, disease organisms and weeds; and excessively wet or dry soil. Fertilization will not correct those problems, so be certain that you know the cause of the symptoms and treat them appropriately.
Having your soil tested is one way to determine if applying fertilizer will benefit your azaleas. Information on soil testing is available in HGIC 1652, Soil Testing.
Most fertilizer recommendations are based on nitrogen, which is an important element in plant growth and often the one that is most likely deficient in the soil. Apply 1 pound of actual nitrogen per thousand square feet of root spread area. Up to 2 pounds can be applied with a slow-release fertilizer. In the absence of a soil test fertilize azaleas lightly in the spring and early summer with a complete, extended-release, acid-forming, azalea fertilizer. Look for a fertilizer with nutrients in a ratio close to 2-1-1, such as a 10-5-4
Good quality azalea fertilizers will also contain necessary trace elements. Never fertilize azaleas in the late fall with these high nitrogen fertilizers, as this may delay dormancy and result in plant injury.
Fertilizer examples are:
Complete, acid-forming organic fertilizers are also excellent choices for use on azaleas, and these are great to mix into the soil at planting, as well as for use with spring fertilization. They are typically not as nutrient rich, and because of both the low nitrogen content and inability to burn the roots, they can be used to mix lightly into the soil in the fall at planting. Organic acid-forming fertilizer examples are:
Apply fertilizer to the azalea’s root zone area (area occupied by nutrient and water-absorbing roots) which can extend beyond the drip line or outer-most branches. According to research findings, a shrub’s roots can extend three times the distance from its center to the outermost branches. So, if the distance from the center of the azalea to the outer-most branches is 2 feet, the feeder roots can extend an additional 4 feet beyond the drip line. To visualize the area to be fertilized, imagine the azalea as the center point of a circle with a 6-foot radius (the “root radius”). Trace the outer edge of the root zone area.
Since most azalea roots are located in the top foot of soil, surface application of the fertilizer is adequate. Evenly broadcast the fertilizer with a handheld spreader or a rotary or cyclone spreader over the root zone area. Sweep any fertilizer off the branches and water afterwards to make the nutrients available to the roots.
For azaleas growing in a bed, follow the steps below to determine how much fertilizer to apply over the bed to supply 1 pound of nitrogen per 1,000 square feet. If the shrub’s root zone area is confined by a sidewalk or driveway, reduce the area to be fertilized accordingly.
- Measure the area of the bed, making an allowance for the roots that extend beyond the outermost branches. Let’s assume the bed is 30 feet long and 10 feet wide. The bed area (length x width) is 300 square feet.
- Determine how much fertilizer to apply over the bed to deliver 1 pound of nitrogen per 1,000 square feet using this equation:
|100||=||Number of pounds of fertilizer required per 1000 square feet in order to apply 1 pound of nitrogen|
|%N in bag|
Assuming you have a 12-6-6 fertilizer, the equation for this example would look like this:
|100||=||8.33 lbs of fertilizer required per 1000 ft²|
Since the root zone is 300 square feet, the actual amount of fertilizer to apply is calculated as follows:
|Root area ft²||x||lbs fertilizer per 1000 ft²||=||fertilizer to apply over root area|
|300 ft²||x||8.33 lbs fertilizer per 1000 ft²||=||2.5 lbs fertilizer to apply over root area|
Apply 2½ pounds or 5 cups of 12-6-6 evenly over the mulched bed.
Azaleas do not have to be routinely fertilized during the growing season. Any fertilizer application should be based on their appearance, such as leaf color, growth rate, soil test results and your objectives, such as encouraging growth or correcting a mineral deficiency.
The best time to apply fertilizer is when it will be readily absorbed by the roots of the plant and when the soil is moist, which can be any time from late spring (after new growth emerges) up to early summer. Avoid fertilizing plants stressed by drought during the summer months. Without water, plants are unable to absorb nutrients, so it is best not to fertilize if water is unavailable.
There are two pruning techniques used for azaleas: thinning and heading. Thinning refers to the removal of branches back to the main trunk or another branch. This method is used to remove leggy branches that extend beyond the canopy of the plant, remove damaged or diseased wood, or reduce the size of the plant. Thinning allows light to penetrate the shrub, encouraging growth on interior branches. You can thin at any time of the year without causing significant impact on flowering, growth or cold hardiness of the plant. However, to reduce the impact on flowers the following year, prune just after flowering in the spring.
Heading refers to the cutting back of a branch, not necessarily to a side branch. This method is used to reduce the size of a plant, create a hedge or to renew old overgrown plants. Renew overgrown plants by cutting them back to within 6 to 12 inches of ground level. This practice results in abundant new growth by midsummer.
The best time to renew azaleas is before spring growth begins. This allows sufficient time for next year’s flower buds to form in midsummer, and for new growth to mature and harden off for winter. Renewal pruning before spring growth, of course, means that flowers are sacrificed for that year.
After renewal pruning, prune the tips of new shoots when they are 6 to 12 inches long, to encourage branching and a full canopy. Thin out new shoots emerging from the old stem. Keep the soil moist during the period after severe pruning.
The most common diseases on azaleas in South Carolina include petal blight, leaf gall, leaf spots, dieback, and root and crown rot. The most common insects are lacebug and spider mites. Good cultural practices such as careful plant location, provision of good aeration and drainage, mulching and good watering habits will reduce the incidence of disease and insect damage. For more information on disease and insect problems on azaleas, refer to HGIC 2050, Azalea & Rhododendron Diseases, and HGIC 2051, Azalea & Rhododendron Insect Pests.
Iron is essential for healthy azaleas. Iron is available for uptake by azaleas when the soil pH is low (acidic). When soil pH is too high (alkaline), iron becomes unavailable and chlorosis, or yellowing of the youngest leaves, may occur. A telltale sign of iron chlorosis is when the area between the veins is yellow or light green, while the veins are darker green. Application of iron as a foliage spray will usually give quick, temporary results when applied during the growing season.
In low pH soils, such as the clay soils in the Piedmont area, iron is readily available. In these soils, chlorosis is usually due to other causes, such as waterlogged or compacted soil, root rot, or injury caused by nematodes or too much fertilizer. The first step to determine the cause of yellowing is a soil test to determine the soil pH.
Azaleas are susceptible to cold injury, especially when exposed directly to early morning sun after a hard freeze. The rapid thawing of frozen branches and twigs may result in bark splitting. Sudden early freezes in the fall and late freezes in the spring also cause bark-splitting. It may take several months before the branches die back on winter-injured azaleas with split bark. Prune out affected branches. To reduce chances of bark-splitting, plant only azalea varieties known to be hardy in your area.