How to grow native azaleas
When it comes to growing native azaleas in the U.S., gardeners should give them plenty of light, avoid planting too deeply and keep young plants well-watered.
Wed, Apr 11 2012 at 3:46 PM
IN FULL BLOOM: A native azalea, Rhododendron canescens, flowers beside Murphy Candler Lake in suburban North Atlanta. (Photo: Tom Oder)
Nationally known native azalea authority Ernest Koone III still remembers one of the first things he ever read about these spring- and summer-flowering plants. It was the first sentence in a small, undated booklet, and he was just 11 or 12.
"The native azalea species of the Southeastern United States have been called, by many plant authorities, the most beautiful of all our indigenous shrubs."
The booklet was written by Fred Galle, longtime director of horticulture at Callaway Gardens in Pine Mountain, Ga., where the Plumleaf azalea, Rhododendron prunifolium, is the signature plant.
The statement “has become a part of me,” says Koone, president of Pine Mountain’s Lazy K nursery, the largest producer of native azalea species and cultivated varieties in the country. “Absolutely no other native American plant group compares with the native azaleas in variety and brilliance of color and fragrance, on shrubs large and small with bloom-times from early spring to late summer.
Here are tips from Koone about how to grow azaleas, the most native of American plants.
Most of the 17 species of native azaleas occur from Texas to Florida and along the Eastern Seaboard from the coast into the Appalachian Mountains up to Virginia. The natural range continues north up the Atlantic coast into Maine and Canada. A single western species found in California, Washington and Oregon, R. occidentale, is very difficult to grow east of the Mississippi. One species, R. canadense, grows from New Jersey northward into Canada.
Many native azaleas — R. prunifolium (plumleaf azalea), R. atlanticum (coastal azalea) and R. vaseyi (pinkshell azalea) — are very cold hardy and can grow far outside of their natural Southern range. Others, such as R. canadense, which grows from north of New Jersey to Labrador, won’t grow well south of New Jersey. High elevation Southeast plants, such as R. prinophyllum (roseshell azalea), won’t do well in lower elevations, even in the Southeast. In these cases, summers are too hot. Conversely, some southernmost species — R. austrinum (Florida flame azalea), R. canescens (piedmont azalea) and R. alabamense (Alabama azalea) — will grow in northern climates but they often won’t flower there because the buds, which form in the summer, will freeze before they can open in the spring. Exceptions can be obtained and plants can bloom a considerable distance from their native range by siting them in appropriate micro-climates.
The most common mistake in planting native azaleas is thinking that these are shade plants and underestimating how much sun they need to bloom well. Early bloomers (March-May) and middle season bloomers (May-June) do best with at least a half day of sun. Late bloomers (July-August) need afternoon shade because of the intensity of the summer sun.
How to plant
Native azaleas need a well-drained, acidic, humus-rich garden soil. To achieve this, amend the soil with organic matter such as ground pine bark, fine pine bark or a bark-based soil additive. A soil pH of 5.0-6.0 is ideal. Because azaleas are shallow-rooted, plant the root ball slightly above the soil surface. Mulch lightly, preferably with pine straw.
Keeping young plants well-watered for the first two years while they establish root systems is critical. A rule of thumb: Keep the soil gently moist. Azaleas cannot tolerate standing water.
A high-nitrogen fertilizer, such as 12-6-6, is recommended. Plants should be fertilized in spring when new leaves emerge and again just before July 4. Don’t fertilize after Independence Day because that will stimulate additional new growth late in the season that could get killed by frost.
Many native azaleas can grow into small trees 12 feet tall or higher. With judicious pruning, they can be formed into bushy shrubs and kept six feet tall or less. Flower buds form in June for the next year's bloom — so prune early and mid-season bloomers immediately after the flowers fade. Prune late-season bloomers any time.
There are three common mistakes in planting native azaleas. They are:
Placing plants in too much shade.
Planting too deeply.
Watering insufficiently while plants are getting established.
Why pick natives?
Native azaleas are different in several key ways from the azaleas seen most often in garden centers. Non-native azaleas sold in nurseries are bred with plants from Asia. These are small-to-large, evergreen shrubs, whereas native azaleas are deciduous and can grow into small trees. Many native azaleas are distinctly fragrant, whereas the Asian plants have almost no fragrance. Native azaleas have a greater range of colors than the evergreens — there are no yellow or gold shades in the evergreens.
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