How to Grow and Care for Azaleas

Rhododendron spp.

Beloved for their delightfully bright and long-lasting flowers, azalea shrubs make a dazzling statement in the spring garden. But there are also varieties that flower in early summer and early fall.

So, with a bit of planning, and a large enough garden, you can enjoy those delicious blooms for up to eight months!

Some are attractively fragrant, with a spicy or sweet, fruity aroma. And the foliage provides pretty fall colors as well.

Shrubs are available in a range of sizes and shapes with a clean, contained profile that requires little maintenance.

And with over 10,000 registered cultivars, there’s a wide selection to choose from.

In this guide, I’ll cover everything you need to know to cultivate azaleas in your garden.

Here’s what’s to come:

What Are Azaleas?

Azaleas belong to the Rhododendron genus, and they are members of the heath family (Ericaceae).

Sometimes they’re classified into two distinct subgenera, Pentanthera and Tsutsusi, other times they’re two of the three main groups that make up the Rhododendron genus.

For the home gardener, what’s important to remember is that they fall into two types: deciduous and evergreen.

Most evergreen varieties are native to Japan, with a few species each from China, Korea, and Taiwan.

The evergreens grown in home gardens are typically hybrids developed for improved qualities such as disease resistance, flowering time, and cold or heat tolerance.

The deciduous species are native to eastern Asia, eastern Europe, and North America.

Several native North American species grace our gardens, such as Florida flame (R. austrinum) and pinkshell (R. vaseyi). And other native species are used for breeding purposes.

Plants are often grouped according to their bloom time, which may be early, midseason, or late.

The early bloomers typically flower from late winter through early spring. Midseason types flower in late spring, and the late group blossoms from early summer through fall.

Planting an assortment of different cultivars and species in your garden is an excellent way to enjoy their floral display for the entire growing season.

Check out our guide to azalea bloom times to learn more. (coming soon!)

Cultivation and History

Ancient artists and poets of both China and Japan have long celebrated the beauty of azalea flowers.

In Japan, where most of the Asian varieties hail from, gardeners at Buddhist monasteries and royal palaces have cultivated and bred these ornamentals for over 500 years.

The first recorded mention dates to the 15th century and Japanese classifications were first codified in 1692 in a text titled Kinshu Makura, which translates to “A Brocade Pillow.”

Dutch traders first introduced Japanese species into Holland in 1680. Later, the British imported species from China. And in 1690 in Virginia, English botanist John Bannister recorded the first of several American species, the delightful R. viscosum, or swamp azalea.

Early American and British collectors quickly jumped on the azalea bandwagon, sending plants and seeds back to Europe for breeding purposes.

But it wasn’t until 1825 in Ghent, Belgium, that the first hybrids from North American stock were successfully produced and recorded, with cultivars coming back to North America in the mid-1800s.

In their native habitat, species plants typically thrive in Zones 5 to 9. But in the mid-1950s, breeders at the University of Minnesota developed the first cold hardy cultivars, significantly expanding their range of use in the garden.

Today, plants from the Northern Lights series are the hardiest that are commercially available, with a selection of outstanding cultivars suitable for chilly Zones 3 and 4.

Propagation

You can grow azaleas from seed. But because most of the available stock are hybrids, seedlings rarely reproduce true to the parent plant.

The only way to ensure a clone of the parent plant is to propagate vegetatively, via stem cuttings or stem layering.

Evergreens are the easiest to propagate from cuttings, while deciduous varieties typically give the best results when layered.

From Stem Cuttings

Ideally, you’ll need to take semi-hardwood cuttings. This is the wood that’s still flexible, midway between tender new shoots and mature wood.

• In spring, right after flowering, collect cuttings five to six inches in length taken from stem tips. Choose stems of one-year old wood that’s semi-flexible – they should bend without snapping.
• Remove leaves from the lower half and trim cut ends to just below a leaf node.
• Lightly scrape the bark for two inches above the cut end with a sharp knife – just enough to remove the outer bark in a few spots.
• Dip the cut end into powdered rooting hormone and gently shake to remove the excess.
• Insert the lower third of each stem into a small container filled with a moist rooting medium, such as a combination of one-third compost, one-third peat moss or vermiculite, and one-third sand.
• Set containers in a sheltered spot in the garden with bright, indirect light.
• Water regularly, keeping the potting medium moist but not waterlogged.
• Roots form in four to eight weeks, and new plants can be transferred to larger pots as needed.
• Keep the containers in a sheltered spot in the garden until they can be planted out the following spring. Provide shelter in spots such as cold frames, against foundations, or tucked under trees and shrubs.
• Provide winter protection such as a mulch of pine needles or straw or a cloche to protect against frost as needed.

Layering

Layering is an easy process that involves encouraging root development on a stem that’s still attached to the parent plant.

The best time to layer is in early spring before leaves have emerged, but early fall works as well.

Spring layered plants can be transplanted into the garden in the fall of the same year. But with either spring- or fall-layered plants, waiting a year or two before transplanting is better.

This allows new plants to mature and gain size quickly in a familiar environment so that they continue to thrive when moved to a new location.

• Choose a lower branch that’s long and flexible enough to easily bend and reach the ground without snapping. Two to three inches of the stem should make contact with the soil (this section is known as the contact stem). The stem tip should extend above ground for six to eight inches.
• At the point where you want the contact stem to produce roots, gently scrape away about an inch of the outer bark.
• Dip the wounded section in powdered rooting hormone and shake off the excess.
• Prepare the rooting area by digging a shallow trench three to four inches long.
• Place the contact stem in the trench and cover it with soil.
• Use a landscape pin or place a rock on top of the buried section to ensure it stays in place.
• Roots form after six to 12 weeks. If you feel resistance from a gentle tug on the stem tip, that is a sign that it has taken root.
• Allow plants to root in place for up to two years.

To transplant, snip the parent stem close to the ground.

Using a spade or trowel, loosen the soil around the contact stem, digging in just outside the dripline of the new plant.

The dripline is an imaginary circle that extends from the furthest branch tip all the way around the plant. Use this as a guide when digging up young shrubs – root growth is typically contained within the dripline.

Gently lift the root ball and transplant to its new location as described below.

Transplanting

Potted shrubs are best planted in spring or fall. For a showy display, they require the right amount of light, and soil with an acidic pH that’s moist and well-draining.

Here are the planting steps:

• Before transplanting, water the plant thoroughly – it’s very difficult for a dry root ball to absorb moisture once it’s in the ground.
• Create a planting hole two to three times the width of the root ball and the same depth as the container it’s currently growing in.
• Mix in plenty of organic material such as well-aged compost, leaf mold, or shredded pine bark until the soil mixture is one-third to one-half organic humus.
• Carefully remove plants from their pots and examine the roots. Gently loosen and separate them, to encourage new growth.
• If the plants are root bound with a dense mat of fibrous roots visible on the surface of the pot, use a clean, sterile knife to slash the mat in four to six spots. Cut about two inches deep and space the slashes evenly around the root ball.
• Place in the hole, and check to ensure that the soil is level with the ground. Avoid sinking the root ball below the ground level to prevent roots from standing in water. Backfill with amended soil and gently firm in place.
• Apply a generous three to four-inch layer of organic mulch – pine bark, pine needle straw, shredded leaves, or straw. Create a mulch-free well around the stem base to keep the wood dry. This helps prevent rot and keeps rodents from nibbling the bark.
• Water slowly and thoroughly, allowing the soil to absorb the moisture without runoff.

Plants can be spaced two to five feet apart, depending on their mature size.

Space two feet apart for plants that grow up to three feet at maturity, two to three feet apart for plants up to five feet, and three to five feet apart for those greater than five feet.

How to Grow

Providing the correct lighting is a key factor to consider when planting azaleas.

Too much sun and they’re going to shrivel up and suffer, but too little light and you’ll have a flowering shrub without any flowers on it!

Dappled sunlight is the solution.

You’ll want to place these shrubs in an area that receives either morning light with afternoon shade or in a position where they receive varied levels of sunlight throughout the day. About six hours of sun in total, spread across the day is ideal.

A location with hot afternoon sun can be tolerated, provided the soil is kept consistently moist. But be careful – the leaves of some species will fade from prolonged, intense sunlight.

Avoid planting close to south- or west-facing walls – radiant heat from wall surfaces can cause moisture loss and stress in hot spells.

Also, avoid locating them directly under trees. Trees do provide filtered shade, but they also compete for water and nutrients, so place your shrubs at the edge of tree root zones.

Rich organic matter in the soil is necessary for plant health, and azaleas prefer acidic soils with a pH between 4.5 and 6.0.

If you’re unsure of your soil’s pH, test the soil before planting and amend as needed with ammonium sulfate or garden sulfur, per package directions.

Good drainage is a must-have for these plants to thrive. Azaleas cannot abide wet feet, so it’s vital to avoid sites that are prone to standing water.

Soil that’s clay based or otherwise heavy and dense retains too much water, and sandy soils drain too quickly.

If your soil is heavy, add one to two shovelfuls of landscape sand or pea gravel to improve drainage.

Conversely, if your soil is sandy, mix in one to two shovelfuls of peat moss. This will help retain moisture, and members of the Ericaceae family love the acidic nature of peat.

If your soil conditions are less than ideal, consider building a raised bed or plant them in containers instead.

You can get the lowdown on how to grow azaleas in containers in this guide.

Whatever the soil texture, before planting it’s beneficial to generously mix compost with the existing topsoil, adding it at a ratio of one part compost to one part topsoil.

Azaleas require about one inch of water per week, so if your rainfall levels are on the low end of the scale, plants will need supplemental irrigation.

When watering, avoid overhead irrigation if possible – it encourages foliar diseases like leaf gall and petal blight.

If overhead irrigation is unavoidable, water in the early morning and allow the sun to dry the wet foliage.

A soaker hose is an ideal option for watering most plants in the garden. Set one up and turn on the hose bib or add a timer for completely hands-free watering.

50-foot Soaker Hose

Soaker hoses are available at Home Depot.

Fertilizing is easy as well. A layer of well-rotted compost applied annually as a mulch will add enough organic material to keep plants well fed and content.

This can be treated with an application of gypsum or even crushed oyster shells, if you’ve got those lying around in your garden shed.

Growing Tips

When provided with the right growing conditions, azaleas are highly rewarding ornamentals that are easy to cultivate and require little maintenance.

Check the following tips to get the most from these lovely shrubs:

• Provide a site with dappled sunlight or morning sun with afternoon shade.
• Ensure an acidic environment with a soil pH of 4.5 to 6.0.
• Create a well-draining site with no standing water.

Pruning and Maintenance

All pruning should be performed in the springtime immediately after the shrub flowers.

Azaleas, like fuchsias, start to form next year’s flower buds shortly after they finish blooming, so pruning in this narrow window is ideal.

If you prune too late, you risk cutting off next year’s buds, which results in fewer flowers.

A measure of the appeal of these plants is their informal growth habit, so attempts to prune them into a boxy shape will be ineffective.

Hard pruning should also be avoided because it results in irregular patches of flowers. After they’ve been pruned, new growth flushes forward to rejuvenate the plant – but you’ll need to wait two or three years before you’ll see flowers again.

Take a step back and imagine the shape you’re looking for before pruning.

If you’re reducing the overall size of the shrub, check to determine what branch goes where and cut as few times as possible. Remember, you can take it off but you can’t put it back on.

Learn more about how to prune azaleas in our guide. (coming soon!)

Deadheading isn’t required, but you can remove spent blooms to tidy up appearances if desired.

And winter care is straightforward. Reduce watering at the end of the growing season and add a thick, three- to five-inch layer of mulch of shredded leaves, pine needles, or straw to protect roots against freezing and thaw cycles.

If unusually cold weather is forecast, plants can be covered with a porous material such as burlap or an old bed sheet to protect against freezing temperatures.

Use landscape pins to anchor covers to the ground until seasonal temperatures return.

For more details, check out our guide to azalea winter care. (coming soon!)

Cultivars to Select

As mentioned, azaleas are generally divided into two types – deciduous or evergreen. And aside from temperature considerations, they all enjoy the same basic growing conditions.

When choosing, remember that evergreen types are fond of warm climates and won’t survive in freezing temperatures. Look to the deciduous species and cultivars for cold-hardy plants.

Now, here’s a sampling of some popular varieties.

Managing Pests and Disease

If your azalea is growing in the right place, you won’t need to worry much about pests and disease problems.

Insects like caterpillars and lace bugs can be hand-picked or treated with an insecticidal soap.

Underground, nematodes can attack the roots. Unfortunately, there’s no treatment for this. Head off problems before they start with a healthy and disease-resistant cultivar planted in the right location.

More serious issues may be caused by bark scale, whiteflies, and leaf miners.

Bark scale blackens branches and appears as small, ashy or white cottony spots and a sticky sooty substance on the wood. Your best bet is to remove the infected limbs and branches, and then dispose of them.

Whiteflies will cause yellow, wilted, and dying leaves. Use neem oil to fend them off.

The azalea leaf miner (Caloptilia azaleella) is a much more serious pest, and dealing with an infestation may require removal of infected plants.

Leaf miners are moth larvae deposited on the underside of leaves. They tunnel inside the foliage and as they mature and feed, small brown blisters appear then leaves brown and curl at the tips and margins.

As for diseases, powdery mildew, caused by Erysipe azaleae, and petal blight (Ovulinia azaleae) are common fungal problems that can generally be controlled with a fungicide.

Powdery mildew appears as a fuzzy white or grey dusting on leaves and stems. Learn more about how to treat powdery mildew in this guide.

Petal blight first appears as small, waterlogged spots on petals that quickly merge, causing flowers to turn slimy and rot.

More serious disease issues include twig blight and rust. Twig blight, a fungal disease caused by Briosia azaleae, results in the buds and twig tips turning brown and dying.

Rust can be caused by one or more species of fungi in the Pucciniastrum genus. It appears as pale green to yellow dots that form blotches of yellow to orange spores.

Removal and disposal of infected leaves and branches is the only safe solution for these infections.

Best Uses

With brilliant flashes of color in a sea of green foliage and delightful structure, azaleas make a perfect statement piece.

They work in mixed beds and borders and are fantastic planted as a flowering hedge. And some of the smaller ones are a standout in rock gardens.

Or try some on the patio in large containers or pots.

For a broad sweep of color, a dozen plants placed together give maximum effect and can be beautifully offset with flowering perennials like black-eyed Susans or a sweep of ornamental grasses.

About Lorna Kring

A writer, artist, and entrepreneur, Lorna is also a long-time gardener who got hooked on organic and natural gardening methods at an early age. These days, her vegetable garden is smaller to make room for decorative landscapes filled with color, fragrance, art, and hidden treasures. Cultivating and designing the ideal garden spot is one of her favorite activities – especially for gathering with family and friends for good times and good food (straight from the garden, of course)!