Azaleas are loosely branched, shade-loving evergreen or deciduous shrubs with elliptical leaves. They bring delightful white, purple, yellow, and red flowers—and all hues in between—to the spring garden when the clusters of funnel-shaped blooms appear. Azaleas need at least four hours of sunlight daily and afternoon shade in places with scorching summers. Keep their soil moist, acidic, and fertile for them to grow well.
Azaleas shrubs are best planted in the spring or early fall. Growth rates vary by species, but most are relatively slow-growing. A one-gallon container plant usually will flower in its first year but may take as much as 10 years to reach its full size. Azaleas are toxic to humans and animals.
|Botanical Name||Rhododendron spp.|
|Mature Size||3–20 ft. tall, 3–20 ft wide|
|Sun Exposure||Partial, full|
|Flower Color||White, pink, purple, red, orange, yellow|
|Hardiness Zones||6-8 (USDA)|
|Native Areas||Asia, Europe, North America|
|Toxicity||Toxic to humans, toxic to pets|
Here are the main care requirements for growing azaleas:
- Grow in loose, well-draining, acidic soil.
- Take soil samples to ensure the soil has an acidic pH.
- Augment neutral or alkaline soils with peat moss to improve drainage and acidify the soil.
- Plant in artificial berms or elevated planting areas with dense soil; it makes the soil more porous.
- Keep soil moist but not soggy.
- Ensure the plant has at least four hours of sunlight; locate it in a shadier spot in a high-heat climate.
Azaleas flourish in a partial shade location in most regions with a few hours of the morning sun. so the flowers don't wilt if a spring day becomes too hot. Azaleas may respond well to full sun in colder climates, while gardeners in warmer climates should give their azaleas more shade.
Azaleas love acidic soil (pH 4.5 to 6.0); this explains why potted nursery plants usually have mostly peat moss as the planting medium. Soil should also have good drainage and good fertility with plenty of organic matter. Azaleas do best with natural mulch, such as pine bark mulch.
Azaleas need water to bloom; spring rain showers usually do the job. However, if the spring is dry, extra watering can be beneficial.
Temperature and Humidity
Azalea hardiness depends on the cultivar, so choosing your plant and planting site is essential. Too cold, and buds may not form; too hot, and flowers may burn from over-exposure. Mildew can be a problem with azaleas; ensure they have plenty of air circulation, and don't plant them too close to other large shrubs.
Azaleas also do well if given some fertilizer. Fertilize in late winter or early spring, no later than the last week of March.
Acidifying fertilizers are a good choice where soils are neutral or alkaline. If you don't know your soil composition, a basic 15-15-15 fertilizer containing equal parts nitrogen, phosphorous, and potassium is your best bet. Another option is a unique fertilizer product made for azaleas, like Espoma's Azalea-Tone.
Types of Azaleas
Azaleas are members of the Rhododendron genus, and similarly, azalea's thick leaves can be evergreen in the South and deciduous in the North. Flowers return year after year, blooming perennially.
Folklore and tradition dictate a particular meaning or symbolism behind flowers. Specifically, azaleas symbolize "Take care of yourself for me," or represent temperance, fragile passion, and womanhood (China).
Azaleas are bred to the unique needs of a particular growing region, and usually, dozens of azalea species and cultivars are available for your climate conditions. Heirloom azalea varieties can grow over 20 feet tall, while dwarf varieties may stay under three feet. Here are some tried and true types:
- 'Rosy Lights': This compact (4 to 6 feet) deciduous cold-hardy shrub blooms in late spring and features a sprightly flower in a rosy red color with hues of coral and blush. This is one of the 'Northern Lights' series of azalea-rhododendron hybrids. The flowers are borne in "trusses"—not as round as traditional rhododendrons but not as diffused as conventional azaleas. It is hardy in USDA zones 3 to 7.
- 'Windbeam': With smaller leaves and a tidy habit (3 to 4 feet), this popular cultivar features bright pale pink flowers and olive green leaves that turn bronze in autumn. Hardy in Zones 4 to 8, it may need shelter from harsh winter winds, but it is more sun and heat tolerant than other azaleas. The spring display is stunning, beginning white and evolving to pink with tiny red freckles on the dorsal lobes.
- 'Golden Lights': The bright golden-orange blooms on this 'Northern Lights' cultivar offer a dramatic color for the spring landscape. Cold-hardy (USDA zones 3 to 7) and compact (3 to 6 feet), the flower trusses are flat and contain ten flowers in shades ranging from butter yellow to orange with salmon-pink highlights.
- 'Golden Oriole': This beautiful hybrid member of the Rhododendron genus has a relatively rapid growth rate and produces orange buds leading to golden-yellow flowers in large showy clusters in early spring.
- 'Fragrant Star': The pure white flowers on this small, 3- to 4-foot mid-spring bloomer have a heady, spicy fragrance. The leaves are a pleasing bluish-green. It is pretty heat-tolerant but not as cold-hardy as others (zones 5 to 9), though it can withstand cold temperatures as low as minus 20 degrees Fahrenheit if sheltered from harsh winds.
- 'Gibraltar': This popular azalea boasts frilly, faintly fragrant, bright orange flowers from crimson buds. It is medium height (4 to 5 feet ) and relatively cold hardy (zones 5 to 8). This variety is also mildew resistant.
Pruning is not mandatory with azaleas, as they show to best effect when allowed to have a slightly informal growth habit. That said, azaleas can benefit from mild pruning that will force bushier, fuller growth. Azaleas start forming buds in summer, so the best time to prune is right after the flowers drop off in late spring.
Deadheading spent flowers will help the plant look tidier and will help direct the plant's energy into green growth. However, it must be done carefully, as the buds for next year's flowers are already developing just below the current flowers. It is too easy to pinch off the future buds if you're not careful.
Although it is a slow process, azaleas can be propagated by stem cutting or layering. Rooting stem cuttings is generally the more straightforward method for most gardeners; here's how:
- In late spring, cut five-inch-long flexible tips off the ends of the supple new stems. Pick off all but the top leaves.
- Scrape off the bark from the bottom one inch of the cutting, then dip it in rooting hormone.
- Plant the cutting in a rooting medium, such as a 50-50 mixture of peat moss and perlite; or sand, vermiculite, and peat moss. The rooting medium should be more porous and draining than most standard potting mixes. Use a pot at least six inches deep; a one-gallon plastic pot makes an ideal container.
- Moisten and pack the rooting mix around the cutting, then place the entire container in a large plastic bag or another clear container. Put the pot in a location that gets bright light but not direct sunlight.
- Check periodically to see if the cutting has rooted (tug gently on the stem to see if you feel resistance). Within four to eight weeks, the cutting should develop a good network of roots.
- When roots have developed, remove the plastic and continue growing the shrub in its pot, feeding every month. Leave the new shrub in its pot through the winter and well into the following spring. It should be ready to plant when new growth is evident. For the winter, the pot should be moved to a protected location, such as a cold frame or an unheated porch.
More advanced gardeners can try the layering method; here's how:
- In late spring or early summer, identify a flexible branch that can be bent to the ground, then dig a shallow trench in the soil below the branch.
- Bend the branch down into the trench so the free end extends up into the air, then pin the underground portion in place with stakes, wires, or heavy rocks. Fill in the trench with soil. It can help to scrape off some of the bark and sprinkle rooting hormone over the wound.
- Leave the layered branch in place for at least a year. During this time, the underground portion of the branch will develop roots.
- When roots have developed, sever the buried branch from the parent shrub, leaving a rooted shoot that can be carefully dug up and transplanted into a new garden location.
How to Grow Azaleas From Seed
Azaleas will grow easily from commercially purchased seeds or seeds you collect from seed pods when flowers drop. Growing from seeds is slow, requiring at least two or three years before the new shrubs flower. For this reason, seed-starting is not often attempted by amateur gardeners. And be aware that offspring produced by seeds from hybrid shrubs may not look like the parent plant. However, for pure azalea species, seed propagation does work predictably. Here's how to do it:
- Collect the seed pods as they turn brown after the first fall frost.
- Dry the seed pods indoors until they split open, then collect the tiny seeds and clean them.
- In winter, fill a seed flat filled with a mixture of sand and peat moss (or commercial seed-starter mix), moisten it, then sow the seeds over the surface and cover the tray with a clear plastic lid and place it in a warm, bright location, but not in direct sunlight.
- The seeds typically germinate in two to six weeks. Thin them out and space them out at least two inches apart.
- When the tiny seedlings have developed two sets of true leaves, transplant them into small individual pots.
- Cover the pots with plastic and continue growing them in a sunny location. Within a week or two, the plastic can be removed.
- As the weather warms, move the pots outdoors.
- After one full growing season, repot the plants into one-gallon pots for another year of growth—or, if they are sizable enough, transplant them in the ground in the fall.
Potting and Repotting Azaleas
Smaller varieties of azaleas can be excellent choices for container culture. And growing in pots can be a good option when your garden soil isn't suitable for growing azaleas.
Use a big pot at least 16 inches in diameter and 12 inches deep. Heavy materials such as ceramic or concrete are best, as they will resist tipping. The growing medium must be light, well-draining, and acidic in pH. A commercial peat-based potting mix blended with extra perlite or vermiculite often works well.
If transplanting from a pot into the ground, dig a hole as deep as the container and about twice as wide, and blend in some peat moss and compost to improve the soil texture and pH.
Feeding azaleas should be reduced after midsummer, and watering should also be somewhat reduced in early fall to toughen the plant up for winter. But after a few hard frosts, it's a good idea to water deeply to hydrate the plant, which will help prevent winter burn.
If you live in a USDA zone that is borderline for the variety you are growing, apply a three- to five-inch layer of dry mulch over the plant's root zone after it goes dormant. Keep the mulch slightly separated from the plant's trunk. This mulch should be removed in spring after the soil warms.
If azaleas show signs of winter damage in your regions, such as split bark, you may need to protect your shrubs over winter by tenting or draping them with burlap. This is not a very attractive solution, so choosing varieties known to be cold-tolerant in your region is best.
Common Pests and Plant Diseases
The pests and diseases most likely to affect azaleas will vary greatly depending on the species and region you're growing it in. Overall you should be resigned to the reality that azaleas can be susceptible to quite a large number of insect and disease problems:
Various aphids, borers, lacebugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips, and whiteflies can all attack azaleas. A horticultural oil such as neem oil can address these pests, though if left alone, insect pests may eventually be controlled by beneficial predatory insects.
Various diseases can attack azaleas, including canker, leaf spot, rust, and powdery mildew. Often these are merely cosmetic and not life-threatening, though they can be treated with fungicides. But there are also very serious root rot fungal diseases, such as Phytophthora root rot, that cause leaf wilting, stem dieback, and eventual death of the shrub. Root rot diseases occur most often in dense, wet, poorly drained soils, but if your landscape is host to these fungi, you may be unable to grow some azalea cultivars. Look for varieties known to be resistant to common fungal diseases—or choose a different type of shrub altogether.
How to Get Azaleas to Bloom
A mature, healthy azalea in a favorable location will usually bloom with no intervention, but if yours doesn't, possible reasons might include the following:
- Too much nitrogen is causing the shrub to add vigorous green growth but at the expense of flowers. If you feed your shrubs, use a balanced 5-5-5 or 15-15-15 fertilizer. Or, use an acidifying fertilizer designed for these plants, such as Miracid.
- Too little sun can cause azaleas to withhold blooms. These plants generally perform best in dappled shade but with some direct sunlight in the morning.
- Root-bound plants may refuse to bloom. This is most likely to occur with potted azaleas, but if a container-grown plant is root-bound when you plant it, it may not bloom. When planting, always examine the root ball, and tease apart or slice through the roots if they are tightly wound around the inside of the container.
- Improper deadheading or pruning can cut off the early-forming flower buds. If deadheading, take care to remove only the dead petals.
Most azaleas bloom in mid spring (mid to late April), but some bloom earlier or later, and it's easy to choose a variety for any design need.
How Long Do Azaleas Bloom?
Most azalea varieties stay in bloom for about two weeks, barring rain or wind damage from a storm.
What Do Azalea Flowers Look and Smell Like?
Azaleas have small, 2- to 3-inch funnel-shaped flowers in white, pink, peach, orange, yellow, purple, or red varieties. Some azaleas have no fragrance, while others might smell like honeysuckle or slightly like carnations.
How to Encourage More Blooms?
If you get the "Encore" variety of azaleas, your spring-flowering azaleas may rebloom again in the fall. Otherwise, you can only expect your azaleas to bloom once. To encourage the most blooms each season, give ample water, make sure your plants are in dappled shade, prune just after flowering (not later in the season when you might prune away new bud growth), keep the soil acidic, moist, and well-draining, and give fertilizer.
Deadheading Azalea Flowers
It is not necessary to deadhead azaleas. They will fade and drop on their own. However, if you want to prevent the flowers from dropping seeds, deadhead them or pluck the faded petals off the plant as they start to turn brown.
Deadheading is best done within three weeks after the bloom period. Take care not to remove any pale, fuzzy buds curled tightly on the tips of branches (those are your buds forming for next year).
Common Problems With Azalea
Azaleas are temperamental, requiring specific growing conditions. They often have frequently reported cultural symptoms.
Evergreen Azalea Has Burned Leaves in Spring
This is a classic sign of winter burn, which occurs when a shrub is exposed to frigid winter temperatures or desiccating winds. Prune off the dead growth; the shrub usually recovers just fine. But if this is a frequent occurrence, you may find it necessary to shield the plant over the winter months. Winter burn and dieback are more often seen with evergreen varieties.
Branches Die Back, One at a Time
This is a symptom of a dreaded root rot fungus, Phytophthora. These diseases cause the roots to constrict, preventing water from reaching the branches. Once such a fungal disease is present in the soil, you may find it impossible to grow some types of azalea. There is no cure for root rot, but you can reduce its likelihood by ensuring the soil is well-drained.
When the leaves on azaleas or rhododendrons show yellowing but with visible darker green veining, it is likely chlorosis. With azaleas, this is the result of alkaline soil that causes an iron deficiency in the plants. Often, feeding the shrubs with an acidifying fertilizer will help relieve the condition. Acidifying amendments, such as peat moss, pine needles, or agricultural sulfur, can also help.
Flower Petals Collapse Just After Opening
This results from an airborne fungus that overwinters on and around the plants. Clear away old mulch and plant debris early in the spring, then spray the plants with fungicide as the flowers are just opening.
What is the difference between azaleas and rhododendrons?
In the garden industry, the names "azalea" and "rhododendron" are often used interchangeably. Azaleas are members of the Rhododendron genus, so all azaleas are rhododendrons, but not all rhododendrons are azaleas. You can tell them apart by flower size and shape and leaf size and color.
Traditional rhododendrons have large round clusters of flowers, while azalea blooms are more evenly distributed on the entire shrub. Rhododendron leaves are also larger, fleshier, and darker green than azalea leaves. To confuse matters more, you can find many hardy azalea-rhododendron hybrids in a wide range of flower colors.
How long does an azalea shrub live?
A healthy shrub in a favorable location can live for many decades. Lifespans of 50 years—or even a century—are quite common.
Aren't azaleas used as houseplants?
Some miniature azaleas are bred to be grown as houseplants. These are typically referred to as "greenhouse azaleas." Often grown as one-time seasonal bloomers, getting them to rebloom is difficult. Greenhouse azaleas are not amenable to being transplanted into the garden after they have bloomed indoors.
Standard garden azaleas are not well-suited for moving indoors to grow as houseplants. Azaleas typically require a winter chill period to set flower buds, and they can be extremely prone to pest damage when moved to an indoor location.
How should I use this shrub in the landscape?
Azaleas look great planted beneath trees or at the back of a border. They can also make a great specimen planting by an entrance or patio in a prominent place. Since the flowers are so showy, ideally, you want your azaleas to bloom when your garden needs a boost of spring color. Maybe after your early-blooming daffodils are fading and before the peonies light up? Some reblooming cultivars (the 'Encore' series) will give you more blooms later in the summer or early fall.
Azaleas and rhododendrons. Poison Control: National Capital Poison Center.
Flowers and their meanings: The language of flowers. Iowa State University Extension and Outreach.
Phytophthora Root Rot in Azaleas. University of Illinois
Chlorosis. Wisconsin Horticulture Division of Extension