US National Arboretum

 


I planted a new azalea and it died. What did I do wrong?

It may have simply dried out. If you plant azaleas in late spring, it is very important to give them some extra water while they are growing new roots. Never let the soil completely dry out it's best to keep the soil evenly moist. Too much water or poorly drained soil might be another explanation of sudden azalea death. Azaleas have very fine, fibrous roots that are easily damaged by waterlogging, even for short periods of time. Before you plant your azalea, dig a hole and fill it with water. If the water has not drained out of the hole within one hour, the soil is poorly drained and you must correct the drainage problem before planting. Install a perforated pipe or drain tile in the garden, making sure that the outlet is lower than the bottom of the planting hole, or build raised beds.
 
 

Can you tell me how to plant an azalea?

picture of curator planting an azalea Plant your azalea in early spring or early fall. If your soil is loose, well drained, and has lots of organic matter, planting will be easy. If drainage is poor, you'll need to correct the drainage problem or plant in raised beds. You can work in some well-rotted leaf mold or compost if the soil is short of organic matter. Don't worry about preparing the soil deeply since azalea roots are shallow and most are found in the top foot of soil. Instead, loosen the soil in a broad area around the planting site. If a soil test reveals that your soil is strongly alkaline, work in enough iron sulfate or ammonium sulfate to drop the pH to 4.5 to 5.5; your state's soil testing lab can give you guidance on how much of these materials are needed to acidify your soil. Water the pot thoroughly before planting and tease the soil away from the roots on the outside of the pot. Don't worry about injuring the roots it's more important to remove a significant amount of the potting soil than it is to keep every root intact. Plant the azalea slightly higher than the surrounding soil since it will probably settle after planting. Finally, water the whole area thoroughly and apply a thin layer of shredded leaves, pine needles, or pine bark to keep the soil cool and moist. Water your newly planted azalea weekly if the weather is dry, at least for the first year.
 
 

An old, established azalea died in my garden. What might have caused its death?

There are several possibilities. Voles, also known as meadow mice, may have chewed on the bark and roots near the crown of the plant. Sometimes they chew all the way around the trunk and kill the inner bark, resulting in death of the whole plant. Keep mulch away from the trunk to discourage voles. The bark may also split when there are wide fluctuations in temperature in the winter. Azaleas may begin to come out of dormancy if late winter weather is warm; if a cold snap follows, bark injury is likely, especially in sunny, exposed sites. Prolonged drought weakens plants and often results in the appearance of fungal cankers on the branches of older azaleas. Look for branches that wilt in hot, dry weather in late summer and be sure to water azaleas if drought drags on more than a few weeks. Prune out the affected branches to stop the spread of fungal canker diseases.
 
 

What should I use to mulch my azaleas? Should I amend the soil at the time of planting?

You can mulch azaleas with shredded leaves, leaf mold, pine needles, or pine bark mulch. Don't use shredded hardwood mulch since it often drives the pH upward. Pine bark is especially useful since it can lower the pH where it is too high, but it is best used on relatively flat ground since it's light in weight and tends to float away in heavy rain.

You only need to amend the soil if it is devoid of organic matter or if the pH is too high. Have a soil test done by your local extension service to determine if something needs to be added. A light amount of well-decayed organic matter dug into the top layer of soil is helpful for retaining moisture and preventing compaction.
 
 

How and when should I prune my azaleas?

Prune azaleas just after they have finished flowering. Remove individual branches back to the spot where they join a larger branch. New flower buds for next spring's bloom are set by midsummer, and any pruning after mid-June could result in diminished flower production next year. Avoid shearing azaleas since it results in a proliferation of unhealthy, twiggy growth. Check azaleas for wilting or dead branches in late summer that may be the result of fungal cankers. These branches should be pruned back to clean white wood that is not infected while the weather is dry to prevent the spread of diseases. Old azaleas that have grown too large for their space in your garden can be brought down in size by cutting the large branches back severely. New growth will spring from the stubs that are left.
 
 

What is the difference between a rhododendron and an azalea?

Taxonomically, Rhododendron is the correct genus name for all azaleas and rhododendrons. Azaleas generally have smaller flowers, bloom a bit earlier, and have much smaller leaves that may be deciduous or partly so. Rhododendrons usually have larger flowers, bloom later, and have large leaves that persist during the winter.
 
 

When should I fertilize my azaleas? What fertilizer should I use?

Established azaleas often do well with no fertilizer at all. Nutrients are slowly released by any organic mulch that you use, so rely on this as the primary source of nutrients. Excess nutrients may promote larger than normal populations of azalea pests like lace bugs and azalea whiteflies. If your azalea foliage loses its deep green color, test your soil to make sure that the pH is not too high.

If a soil test reveals that nutrients are extremely low, fertilize azaleas in the spring or fall. Use a granular, slow-release fertilizer that is acid-forming and apply a very light scattering around the edge of the root zone of the plant. Never apply more than a few tablespoons at any one time; excess fertilizer can easily burn the delicate roots of azaleas since they are so close to the soil surface. Scorched leaf margins often result from overfertilization.
 
 

Why isn't my azalea blooming?

picture of the walled Morrison Garden Too much nitrogen in early summer may encourage vegetative growth at the expense of flower bud formation, so limit fertilizer applications to the fall or spring or skip the fertilizer all together. Although azaleas are well adapted to partial shade, deep shade produces spindly, weak growth and few flower buds. Azaleas usually won't flower well if planted under trees with dense foliage, such as maples, beeches, and pines. Plant in the diffused light under widely spaced, high-crowned trees like oaks and tulip poplars. Deer and rabbits may eat many of the flower buds as they browse in the winter, particularly if the weather is harsh and other food is scarce. Flower buds can also be damaged by cold, dry winds, particularly when warm winter weather is followed by a period of bitter cold.
 
 

My azaleas always turn yellow or purple in winter. What's wrong?

Nothing is wrong. Like all evergreen plants, azaleas periodically lose some of their foliage, and the leaves may turn yellow, red, or purple before they fall. Often the only leaves that remain are those that surround the flower buds at the tips of the branches. This characteristic is linked to the genetics of the parents used to breed garden azaleas. The degree of leaf coloration or loss is a function of parentage and not the severity of the winter. In unusually cold winters, certain azaleas may lose more leaves than they would in mild winters.
 
 

My azalea foliage looks white, and there are black bugs underneath the leaves. How can I get rid of them?

picture of azalea lace bugs on leavesYou undoubtedly have a problem with the azalea lace bug. This insect hatches early in spring as the new foliage begins to mature and its numbers may build to damaging levels with successive generations. Lace bugs reach their peak in late summer and do their worst in sunny, exposed sites. Spiders are important predators of lace bugs and since they shy away from sunny, hot places, plant your azaleas where there is some shade. Insecticidal soap, horticultural oil, or a systemic insecticide may spare your azaleas the damage if applied in spring when the first hatchlings are noticed.
 
 

All the leaves on my azaleas are notched, and they are growing poorly. I don't see any insect or pest causing this damage. What's going on?

The damage you describe is that of the black vine weevil, a small nocturnal weevil that, in its larval stage, feeds on azalea and rhododendron roots. As the new leaves expand in the spring, adult weevils emerge from the soil and make nightly visits to the leaves to feed, chomping sections out of the margins of the new leaves. Black vine weevils can't fly, so they don't spread rapidly. They spread most commonly in container plants and a few larvae in a single pot may start an infestation that may damage dozens of plants in your garden. Black vine weevils are very hard to get rid of, so quarantine new plants for several months before planting to make sure they are not infested. A pesticide containing imidacloprid may help control them.
 
 

My azalea flowers never last more than a few days in spring. Then they cling to the plants and turn brown. Why?

Wet weather in spring often results in serious damage from a fungus disease called azalea petal blight. Apply a fungicide labeled for petal blight just as the petals begin to show color. If treated at the right time, and if temperatures are not too hot, the blossoms may last as long as three weeks and will drop off the plant instead of turning brown and mushy.
 
 

Can I transplant a large azalea? If so, how should I do this?

Azaleas have very shallow root systems, so even large azaleas may be successfully transplanted. It is important to dig a wide root ball. Don't worry about digging deep into the soil since most azalea roots are near the surface. The best time to do this is early spring or early fall when the weather is cool. Begin by preparing the new planting site. Then dig the azalea, preserving a root ball as wide as can be safely moved. You can lift it onto a tarp and then use the tarp to drag the plant to its new location rather than picking it up. Be sure not to plant the azalea too deeply and water it thoroughly after transplanting.
 
 

I'd like to see the azaleas in full bloom. When should I come to the U.S. National Arboretum?

Peak bloom can vary by two weeks or more, depending on the weather, but usually takes place around the end of April. The earliest peak bloom date reported in the last decade was April 15; the latest was May 4. Keep in mind that many azaleas are in bloom long after the peak and others might bloom early there are usually some azaleas in bloom from early in April until well into June. Before you come, check the Azalea Blossom Watch page to see what is in bloom.
 
 

Where can I find more information about azaleas?

Check out the Azalea Society of America web page at www.azaleas.org. Another good source for information about azaleas can be found at www.theazaleaworks.com. A broader source of information that includes rhododendrons as well as azaleas can be found at the American Rhododendron Society web site at www.rhododendron.org or at the Rhododendron Species Foundation web site at www.rhodygarden.org/index.html.

If you are looking for a particular azalea variety, check the Plant Sources Page for tips on locating a source.

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Last Updated April 20, 2009
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