How To Grow And Care For Azaleas

Rhododendrons and azaleas are arguably one of the Southern gardener's favorite shrubs. Many people think of them as entirely different plants, but they both belong to the genus Rhododendron, which comprises more than 800 species and 10,000 named selections. Even to the untrained eye, one difference between the two groups is noticeable: azaleas generally have much smaller leaves. From a technical standpoint, azalea blooms are typically funnel-shaped and have five stamens, while rhododendron flowers are bell-shaped and have ten or more stamens.

Selecting a species that will thrive in your climate allows gardeners in every part of the South to enjoy these plants—even growing some in containers. While rhododendrons generally do better in the Upper and Middle South, azaleas are more accommodating. With necessary attention to soil, light, and proper selection, these plants can thrive throughout the South. Azalea species can be evergreen or deciduous. Plant sizes vary somewhat within groups, but most individual plants are roughly equal in height and width.

As beautiful as they are, azaleas are toxic to both humans and animals. They contain a toxin called grayanotoxin and arbutin glucoside. Humans who ingest these toxins may experience mild to severe symptoms such as nausea, vomiting, difficulty breathing, abnormally low blood pressure and heart rate, and cardiac arrhythmia. According to the American Society for the Prevention of Cruelty to Animals (ASPCA), azaleas are toxic to dogs, cats, and horses and can cause diarrhea, vomiting (not in horses), weakness, and cardiac failure.

Plant Attributes

Azalea Care

Azaleas are generally low-maintenance plants that will thrive in most yards when planted in the right location and with a bit of basic care. With proper care, azaleas can live for decades—or even longer. The Azalea Society of America notes that there are azaleas in Japan that have thrived for centuries!

Light

The sun tolerance of azaleas varies by species and selection. Most types generally prefer the partial sun or filtered shade beneath tall trees. The east and north sides of a house are generally good locations. Too much sun bleaches or burns the leaves, and too little results in lanky plants that don't bloom. Make sure to position plants in partial sunlight to prevent compact shrubs in heavy sunlight or lack of blooms in deep shade. Avoid varieties that love the sun if you live in a climate susceptible to cold winters with heavy snowfall. Choosing a suitable plant variety helps azaleas to flourish year after year.

Soil

Azaleas need acidic, well-drained, organically enriched soil that should neither get too dry nor remain soggy. The recommended practice in areas rich in alkaline soil, such as Texas and Oklahoma, is to build raised beds for planting. Create beds 15 to 18 inches deep and fill them with a half-and-half mixture of finely milled bark and coarse sphagnum peat moss (be sure to mix the two thoroughly with water before serving the beds). Irrigating with alkaline water will slowly raise the pH level. To keep it in the desired range of 5.0–6.0, prepare a mixture of three parts garden sulfur to one part iron sulfate, then apply it at the rate of one pound per 100 square feet of the garden bed—this should lower the pH by one point.

Planting in heavy clay is a no-no: root rot often ensues, indicated by yellowing, wilting foliage, and collapse of the plant. Planting in limy, alkaline soil is another mistake—lack of iron quickly results in chlorosis (yellow leaves with green veins). If your existing soil is too bad to fix, plant azaleas in raised beds or containers.

Water

Because they absorb water through their foliage, wet the leaves and root zone when you water. Overhead watering with sprinklers works well, but to prevent fungal diseases, water in the morning so that leaves dry by the afternoon. Avoid drip irrigation―it doesn't wet the root system uniformly.

Temperature and Humidity

Though hybridization efforts have resulted in plants that can tolerate a variety of climates, most azaleas thrive in locations where winters are cool to moderately cold and summers are warm to hot. Generally speaking, azaleas like temps between 30ºF and 85ºF.

Fertilizer & Mulch

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 nitrogen and sulfur, such as Holly-tone 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. Also, don't fertilize before bloom―you'll encourage leafy growth at the wrong time.

If your azaleas need an immediate pick-me-up, switch to Miracle-Gro Azalea, Camellia, and Rhododendron Plant Food. Both roots and leaves quickly absorb this liquid fertilizer, but you'll have to apply it more often than the others.

In spring, just after the blooms fade, apply mulch. Do not mulch in the fall. Mulching will hold heat in the soil and delay the onset of dormancy, increasing the chances of winter damage.

Planting

Plant azaleas with the top of the root ball slightly above soil level. Don't cultivate around these plants, as they have shallow roots.

Types of Azalea

Azaleas are divided into evergreen and deciduous categories.

Evergreen azaleas fall into more than a dozen groups, though an increasing number of hybrids have such mixed parentage that they don't fit conveniently into any category. Our guide to evergreen azaleas features some of the most popular groups. Except as noted, their bloom season is late winter or spring.

Here are types of evergreen azaleas:

• Southern Indian Azalea (Rhododendron indicum): Native to Japan, this compact shrub grows up to 3 feet tall and wide in USDA Zones 5a-7b. Hot pink to burgundy flowers bloom in late spring and in fall.
• Torch Azalea (Rhododendron kaempferi): This Japanese native grows up to 6 feet wide and 10 feet tall in ten years. It grows in woodland and natural areas, Japanese gardens, and containers in USDA Zones 5a-7b.
• ‘Rosebud’ Azalea (Rhododendron ‘Rosebud’): Small and compact, this azalea displays small pink flowers from mid to late spring. It is a Gable hybrid that grows in USDA Zones 6-9.

Deciduous azaleas (sometimes referred to as native azaleas) have a unique beauty that few plants can match, and a number of excellent hybrids have been developed over the years. They feature intense bloom colors that are often lacking amongst evergreen hybrids, so if you're looking for a plant that packs a punch, a deciduous azalea might be the one for you. See our guide to deciduous azaleas for a full rundown of popular hybrids.

Here are types of deciduous azaleas:

• Piedmont Azalea (Rhododendron canescens): Native from east Texas through North Carolina, this is a large shrub that forms clumps up to 10 feet tall. It grows well in USDA Zones 5-9.
• Florida Azalea (Rhododendron austrinum): Attractive to hummingbirds and bees, this native shrub grows up to 8-10 feet tall and wide. It grows in the southeastern U.S. in USDA Zones 7a-9b.
• Flame Azalea (Rhododendron calendulaceum): Native to the Appalachian Mountains from Pennsylvania to Georgia, this species grows 4-8 feet tall in USDA Zones 5a-7b and is the parent of many hybrids.

Pruning

Azaleas, especially those planted near the house, can get too big eventually. This necessitates pruning. Though the mere thought of this terrifies most homeowners, pruning correctly is really quite simple, as long as you remember these tips.

First, finish your pruning by late June. Once you get into July, most azaleas will start setting flower buds. Pruning after that will ruin next spring's floral display. Do any extensive pruning in late winter or early spring if possible. Pruning at this time will sacrifice some flower buds, but it diverts the plant's energy to latent growth buds, which will then be ready to push out their new growth early in the growing season. You can do some shaping while plants bloom—try using cut branches in arrangements.

For evergreen species, cutting the occasional wayward branch restores symmetry. To keep bushes compact, tip-pinch frequently, starting after flowering ends and continuing until mid-June.

Prune deciduous azaleas while they are dormant and leafless. Azaleas don't need as careful pruning as rhododendrons―the leaves are relatively evenly spaced along the branches, with a bud at the base of each leaf, so new growth will sprout from almost anywhere you cut (in either bare or leafy wood).

Propagating Azaleas

There are several reasons why you may want to propagate azaleas. Vegetatively propagating azaleas (e.g., stem cuttings, layering, division) will ensure that the offspring will have the same characteristics as the original plant. Therefore, if you like the plant you have, you can increase your holdings through vegetative propagation. Also, if you like the plant and are concerned it may get damaged, especially from a storm, you can take cuttings in case you have to replace the original plant. Another reason is to be able to take the plant with you if you are moving to a new location and the original plant cannot be moved.

Azaleas can be propagated vegetatively through several methods. Here's how.

Stem Cuttings

1. You will need a sterilized, razor-sharp knife or razor blade, rooting hormone, plastic bags, sterilized potting mix such as the bagged seed starting mix, and water. You will need small, plastic containers with drainage holes, or you can cut off the base of a gallon milk jug and make drainage holes. It is best to do one cutting per small, two-inch container, or maybe two cuttings per four-inch container, or several per milk jug.
2. For evergreen azaleas take the stem cutting in early summer, from June on. The growth on the stem should be the current season's growth that has turned woody about five to six inches down. The stem should be able to bend but not snap off immediately. Cut the top five inches of the stem so that the uppermost is green but the base of the cut is woody. Cut right below the node which is where the leaves are attached to the stem. There is a higher chance of rooting if you cut below the node.
3. For deciduous azaleas, take the cutting earlier in the season when there is active growth and green stems (no woody part). This is from mid-April through May when the plant is in active growth and the stems are soft, green, new growth.
4. A rooting hormone is optional with evergreen azaleas, but highly recommended for deciduous azaleas. When using a powder rooting hormone, dip the cut end into water, shake off the water, dip into the hormone, and then plant.
5. Poke holes into the already moistened growing medium with a pencil. Strip off the leaves of the lower two inches. Insert the cutting so the stem is a few inches deep to be able to stand up.
6. Cover with a plastic bag so the bag is "inflated." Either blow in the bag and seal, or prop it up with wire hangers. The size of the bag and how it will stay inflated will depend on the size of the container.
7. What you are creating for these cuttings is a "mini greenhouse" so the cuttings can root without losing too much moisture. There should be condensation inside the bag. This indicates sufficient moisture to keep the plant turgid.
8. Place these mini greenhouses in an area that is 60°F to 75°F. If they are outside, place in the shade. If inside, either a northern exposure window or under fluorescent lights for 16 hours per day.
9. It will take four to eight weeks for roots to develop. When the cuttings have rooted, gradually open the plastic, a few hours a day, to acclimate the plant. Eventually, when it does not wilt with the bag opened, pot up into a larger container and let it grow in a cold frame or greenhouse until you can plant outside the next season.

Layering

Layering is another method of vegetative propagation that is recommended for evergreen azaleas.

1. You need a trowel and landscape pins, large paper clips, or a large rock.
2. In the spring, identify a flexible, low growing branch. Dig a shallow trench.
3. Encourage rooting by injuring the branch first such as nicking, scraping, or twisting the branch where you want roots to form.
4. Bend the branch down to put in the trench and cover with soil. You may have to "pin" it with landscape pins, large paper clips, or a rock to keep the branch in place.
5. Leave the branch like this is all season long as roots can take months to form.
6. In the subsequent year, when there is a mass of roots, cut the stem off from the mother plant and pot up in a small container. Water and let the plant continue to grow until there is enough root structure to be able to plant in the garden. You may have to let it grow in the shade first to minimize transpiration until it can tolerate the sun and winds.

Division

Division is a method of vegetative propagation that is recommended for deciduous azaleas. Most deciduous azaleas are stoloniferous, which means that underground stems develop and grow away from the plant. These stems send up shoots.

1. During the growing season, look for these shoots.
2. Dig them up, ensuring you have included their own, separate root systems, and pot up in a container with potting mix.
3. Water, place in the shade for a few weeks, and let the new plant grow to have a large enough root system to be able to plant in the garden again.

Important: Before propagating, be sure that your plant is not patented. Patented plants are illegal to propagate. You can check to see if your plant is patent-protected by checking the tag, label, or container. Patented plants will bear a trademark, registered trademark, or patent number by their name.

How to Grow Azaleas From Seed

For the evergreen azaleas that are likely hybrids, growing from seed will produce offspring that will not have the same desired characteristics, such as the same flower color. However, for the deciduous or species azalea plants, this may be an easier way to propagate as many of these are difficult to propagate from cuttings.

1. Collect seed pods in the fall before they open and store in a cool, dry place. When the pods are dry, break the pods to remove the seeds.
2. Insert drainage holes in a clean, plastic container such as a food storage box or shoe box. Fill with seed starting mix and moisten.
3. Sprinkle the seeds on top. Do not cover with the potting mix but mist with water. Cover with the plastic lid.
4. There is no need for light until they germinate but make sure the room is warm, 70°F to 75°F. After they germinate in two to eight weeks, provide the light in the form of fluorescent tubes.
5. When they have developed two to four true leaves, transplant to larger containers to give the seedlings more space to grow. Keep growing indoors, under lights, until large enough to move outside when the danger of frost has passed.

Potting and Repotting Azaleas

In the spring, a common gift is a compact, blooming azalea plant called a florist's azalea. This is an evergreen type of azalea bred to be this compact and forced to bloom in the early spring in a greenhouse. If you received one, make sure the container itself has drainage holes and remove the decorative covering. To prolong the blooms, keep in a cool place, 60°F to 65°F, out of direct light.

If you want to transfer the gift plant to the garden in the summer, the plant may not be cold hardy to survive winters. If you want to encourage it to bloom again, put it outside for the summer, in light shade. Then, bring it back in the house before the first frost. Keep it at 40°F to 50°F for five to six weeks, from November to January, to encourage bud formation. Water enough to prevent wilting and do not use fertilizer. In January, move to an area with bright, indirect light and warmer temperatures of 60°F to 65°F. It should bloom in the early spring.

Growing Azaleas in Pots

Compact varieties such as Encore azaleas do well in pots. Plant in well-drained, acidic soil in a pot large enough to accommodate the plant’s root system. Because azaleas have shallow roots, they need space to spread. Mix the soil with organic matter, and plant the azalea at the same depth or slightly above the soil line. Top with a layer of mulch. Choose a location where the plant gets morning sun and afternoon shade. Since containers tend to dry out quickly, water the azalea regularly to keep it moist. Apply fertilizer every spring. Repot into a larger pot when the roots outgrow the container. During very cold winters, bring the pot indoors and place it in bright, indirect light away from drafts and heating vents.

Overwintering

There are two things you can do for your azaleas before winter to ensure their survival: 1) make sure the plants are well watered, and 2) mulch with an organic mulch. In the late fall or early winter, apply one to two inches of aged wood chips, leaf mold, or pine needles a few inches away from the main trunk. Azaleas have a shallow root system so this will help conserve soil moisture and minimize soil temperature fluctuations. Fertilizing and pruning should have already stopped mid-summer.

Common Pests & Plant Diseases

Insects and diseases seldom bother healthy, vigorous plants. However, that doesn't mean there aren't some problems to watch for. Like many plants, azaleas can be susceptible to powdery mildew, leaf spot, or root and crown rot. Here are a few of the most common issues that plague azaleas.

Diseases

• Petal Blight: Blight attacks an azalea's blooms, turning them brown and slimy and causing them to drop prematurely. The fungi that cause blight thrive in mild to warm wet climates—a good descriptor for many late spring days in the South. If you believe your azalea has petal blight, sanitation is key. Remove infected blooms as well as those which may have already fallen. To avoid spreading the fungus to healthy plants, don't add the infected blooms to your compost pile. In the early spring, before rain hits and blooms begin to appear, apply a fungicide meant to fight blight. Prescribed application of the fungicide, in combination with proper watering, fertilizing, and sanitation practices, should help your azaleas resist blight.
• Azalea Dieback: Two fungi cause dieback: Botryosphaeria and Phytophthora. Phytophthora is a deadly soil-borne fungus that's generally fatal and easily spread. Azaleas with dieback will fail to thrive; leaves will wilt, shrivel, and may turn yellow or red prematurely. Unsure if your azalea has Phytophthora? Take a close look at the bark near the base of the plant. If it's turned a reddish/brownish color, chances are it's been infected with Phytophthora. Botryosphaeria works a bit differently. Rather than affecting the entire plant, you'll likely see dying branches on an otherwise healthy plant.
  
  Treating dieback is simple but brutal. If Phytophthora is the culprit, removing the plant is likely the best way to stem fungal spread. Because Phytophthora is a soil-borne disease, refrain from planting anything else in the same spot until the area has been treated well with a fungicide. If your azalea dieback is caused by Botryosphaeria, prune away all the infected branches, cutting well below the discolored wood to ensure you've gotten all of it. Dispose of infected plant material; don't compost to avoid spreading the fungus. Sterilize your cutting tools between cuts with a 1:9 bleach-to-water solution or rubbing alcohol to avoid spreading the fungus from one area of the plant to the next. Once you've cut away the infected areas, apply a fungicide spray designed to treat dieback as directed.

Pests

• Azalea Lace Bugs: Lace bugs (Stephanitis pyrioides) are among the most common pests of azaleas. Small white flies with clear wings, they perch on the undersides of leaves, sucking sap. They leave hard, black spots on the leaves' lower surfaces, while the tops look speckled and bleached. Lace bugs favor azaleas growing in the sun and go through several generations each year. Infested plants will drop leaves prematurely and may not bloom well.
  
  Because lace bugs hide under the leaves, they're hard to hit with conventional insecticides applied with a sprayer. But I have a strategy that works pretty well. As soon as I finish pruning, I spray my azaleas according to label directions with a systemic insecticide called Cygon. I don't have to hit the bugs directly. The foliage absorbs the chemical, which then goes into the lace bugs. About three weeks later, I sprinkle granulated fertilizer containing the insecticide disulfoton, which provides a good six weeks of control. If any lace bugs show up after that, I spray with Cygon again.
• Azalea Caterpillars: These little buggers start as small green worms that eventually become big yellow-striped munchers with reddish heads and prolegs (the little fleshy abdominal limbs most caterpillars have). Azalea caterpillars (Datana major) feed in big groups and can strip an azalea clean if not caught in time. They are a regional pest that thrives in the South and because they are most active in late summer and early fall, they've earned themselves the nickname "Labor Day" worms. Thankfully, they're pretty easy to get rid of. Shake branches to make them drop and step on them. Or pick them off by hand—they are harmless to humans—and drop them in a bucket of soapy water. If you're still having trouble with azalea caterpillars, you can hit your plants with an insecticide. There are both organic and chemical insecticides meant specifically for caterpillars so take your pick.

How to Get Azaleas to Bloom

A healthy azalea doesn't need much help blooming. It's simply in its nature to show off. So if you want lots of blooms, focus on the basics. Start by making sure your azaleas are planted in the right sun and soil—dappled shade and acidic soil that drains well. If your plant came in a container, make sure to loosen the compact soil around the roots before planting to avoid your azalea becoming root-bound, as that can also stunt bloom production. Seed formation also can reduce next year's bloom, so once your azalea has completed its blooming cycle, clip or break off spent flower trusses, taking care not to damage growth buds at the base of each truss. And don't overfertilize! Too much nitrogen can actually encourage more green leaves than blooms.

Common Problems With Azaleas

Evergreen azaleas are very common landscape shrubs in the South and well worth the show when you see masses of them in bloom. However, they do have a few requirements: moist, well-drained soil with high organic matter; light shade; and a pH range of 4.5-6. Azaleas are shallow-rooted, so they may dry out quickly. They do not like to compete with other plants for soil moisture.

Some of the more common symptoms are listed below.

The azalea leaves are yellow with green veins

This symptom of chlorotic foliage can be caused by several factors, but the likely reason is that the soil pH is too high for azaleas. This makes the iron in the soil unavailable to the plant. Azaleas prefer slightly acidic soil, with a pH range of 4.5-6. You can lower the soil pH by adding ferrous sulfate or finely ground sulfur.

The azalea leaves are not a healthy green, but are speckled and bleached-looking

As mentioned above, this is caused by a very small insect called a lace bug, which usually resides under the leaves and sucks the chlorophyll from the plant. Apply a systemic insecticide.

The azalea leaves have brown or dead margins

This is called leaf scorch and can be caused by insufficient water, too much water (insufficient drainage), or too much fertilizer. Check the soil and roots and see if it is too dry or too wet. If it is too dry, water more often, amend the soil with more organic matter, and mulch. If the soil is too wet, see if something is preventing the drainage, or see if you can lift and raise the plant to be higher. If you think you applied too much fertilizer, see if watering the plant can dilute what you applied and ease back on fertilizing.

The azalea started blooming but then flowers became spotted and died prematurely

As mentioned above, this is petal blight, caused by an airborne fungus that thrives during cool, moist springs. It is best to take a preventative approach for next year. Remove the flowers and any debris below the plant. Remove the mulch and replace it with new mulch. Do not water overhead. Consider purchasing azaleas that bloom later in the year. If you spray with a fungicide, do so in the early spring before it blooms.

The azalea did not bloom at all

Several factors can cause this: 1) too much shade (then give it more sun), 2) poor plant nutrition (add fertilizer specially formulated for azaleas), 3) the plant is not cold hardy to the area (pick one developed for your area), or 4) the buds were pruned off in the previous year. The new buds form in July so if you pruned after mid-July, you may have removed buds that would have produced next year's flowers. If you have to prune, do it right after the azalea flowers.

The azalea bark is damaged and split

This is cold injury and depending on how deeply affected the area is, the plant may not survive. If the branches start to die, then the vascular system has been adversely affected and you may have to purchase a new plant. Consider buying one that is cold hardy to the area. Ensure its winter success by making sure the plant receives enough soil moisture and mulch.