Azalea Society of America

/Home/Garden Types/Flower Gardening/Types of Garden Flowers/Garden Azaleas

Azalea Society of America
700 New Hampshire Ave NW Apt 1011
Washington DC 20037


Azaleas are in the genus Rhododendron, with evergreen azaleas in the subgenus Tsutsusi and deciduous azaleas in the subgenus Pentanthera.

Some small-leaved rhododendrons look like evergreen azaleas. To tell them apart, first look at a flower—most azaleas have only 5 or 6 stamens, while most rhododendrons have 10 stamens.
'Bayou' leaf hairs 'Bayou' leaf hairs Then look at a leaf—azalea leaves tend to be thinner, softer and more pointed than rhododendron leaves, and azalea leaves tend to have long straight hairs parallel to the leaf surface, usually along the midrib on the underside of the leaf.
R. augustinii leaf scales Rhododendron augustinii leaf scales

Finally, using a magnifying glass, look at the underside of a leaf for tiny round structures called scales—azalea leaves never have scales, while small-leaved rhododendron leaves are always covered with scales (the more correct name for small-leaved rhododendrons is "lepidote" rhododendrons, where lepidote means "covered with scales").


azalea variability

Azaleas are either species or hybrids. A species is a population that interbreeds and is reproductively isolated from other populations. Seedlings from such isolated species populations look like the parents, or "grow true from seed". Hybrids are crosses between other species or hybrids. Hybrids will not grow true from seed and may be faithfully reproduced only from cuttings, which are clones of the mother plant.

Azaleas have been hybridized for hundreds of years. Over 10,000 different azalea plants have been registered or named, although far fewer are in the trade. This provides a very wide variety of plant habits, sizes, colors and bloom times to meet almost every landscaping need or personal preference.

All North American species azaleas, also called native azaleas, are deciduous (drop their leaves in the fall), with flower colors ranging from white to purple, pink, red, orange and yellow. Evergreen azaleas, native primarily to Japan, have flower colors including white and various shades of purple, pink, red and reddish orange, but not yellow. Color patterns include single colors and bicolors as well as sectors, stripes and flecks. For many azalea varieties, all the flowers on the plant are similar. For other varieties, the flowers on the plant may be a mixture of color variations, with a different mixture from one year to the next.

R. serpyllifolium R. serpyllifolium 'Satin Robe' 'Satin Robe' Many azalea varieties have 2 to 3 inch flowers, although the size varies greatly on different varieties. Compare the 1/2 inch flowers on R. serpyllifolium with the 2-1/2 inch flowers on 'Satin Robe' and the 4 to 5 inch flowers on 'Higasa'. 'Higasa' 'Higasa'

There are many different flower types, ranging from
- single—a small green calyx at the base, 5 (rarely 6) petals, 5 or more stamens and 1 pistil ('Higasa', 'Kobai'), to
- hose-in-hose—10 to 12 petals, due to the calyx becoming petals ('Satin Robe'), to
- double—a variable number of petals, due to some or all of the stamens becoming petals ('Bob Hill'), to
- double hose-in-hose—30 or more petals ('Balsaminiflorum'). 'Bob Hill' 'Bob Hill' 'Balsaminiflorum' 'Balsaminiflorum'

Different varieties also have different petal shapes, ranging from narrow petals ('Linearifolium', 'Koromo Shikibu') through triangular petals ('Satin Robe') to overlapping rounded petals ('Kobai'). Petal edges may be flat, recurved, wavy or ruffled. 'Linearifolium' 'Linearifolium' 'Koromo Shikibu' 'Koromo Shikibu' 'Kobai' 'Kobai'
'Don's Variegated Austrinum' 'Don's Variegated Austrinum' 'Serenade' 'Serenade'
The length of azalea leaves range from as little as 1/4 inch on a few varieties to more than 6 inches on a few others. Deciduous azaleas normally have large leaves, while evergreen azalea leaves are rarely longer than 1 to 2 inches. Leaves of most azaleas are a solid green, but leaves on a few varieties feature white or yellowish mottling ('Keisetsu', 'Don's Variegated Austrinum') or edges ('Silver Sword'). While leaves of most varieties are roughly football-shaped ('Serenade'), a few are narrow and strap-like ('Linearifolium').

Plant habits of different varieties of azaleas range from stiffly upright (many deciduous varieties), to broad spreading (many evergreen varieties), to irregular. While plant height is around 3 to 6 feet for many varieties, it ranges from under a foot to well over 15 feet for some varieties. A few evergreen varieties ('Pink Cascade') are weeping and may be grown as a hanging basket. Many varieties are dense and compact, others are quite open, and some are almost tree-like.

Most azalea varieties bloom in mid-April to mid-May in the mid-Atlantic area of the United States. A few varieties bloom a month or so earlier, and a few varieties bloom as late as August and September. Blooms typically last for one or two weeks. In warm climates such as the deep south of the United States, some azalea varieties bloom again in the fall. This re-blooming trait is being bred into the Encoreâ„¢ azaleas for reliable fall blooming in colder areas as well.

The azalea search pages make lists of azaleas with the characteristics you like, and show their details, including sources. (Unfortunately, not yet—all it does today is show you how it will work some day, to elicit your comments and suggestions.)


growing azaleas

Azaleas are relatively pest-free, forgiving and easy to grow plants. Their cultural needs include:

* Moderate temperatures (USDA cold hardiness zones 6 to 8, minimum -10 to +20° F.), although many varieties can thrive in much lower temperatures, and others in much higher temperatures.
* High shade is preferable but some varieties do well in full sun, especially deciduous varieties. While more sun typically produces more compact plants with more blooms, the blooms will not last as long.
* Slightly acid soil (pH 5.5-6) is best and is usually found under oak, pine and holly trees.
* A mulch of pine bark, pine needles or wood chips helps to keep moisture in the ground, even out changes in the soil temperature, and keep weeds out. An inch or so around the root zone and a thicker layer between the plants is desirable.
* Azaleas do not like "wet feet". Good drainage is most easily provided by planting azaleas with the tops of their root balls a few inches above ground level and mounding the soil up to the plants. This is particularly important with heavy clay soil.
* Azaleas like moist soil at their roots. This may require supplemental watering through early fall, at least until plants are established in the ground for a few years. Adequate water after bloom helps to produce more flower buds for next year. An infrequent deep soaking is more effective than superficial sprinkling. The amount of water needed depends on the soil, temperature, humidity, wind and sunlight. In a dry fall, water heavily after a good frost, before cold weather sets in.
* Established azaleas do not need fertilizer. To avoid inducing new growth which may be killed in the winter, do any fertilizing in late winter or early spring; never after July 1.
* To avoid cutting off next year's flower buds, do major pruning of azaleas soon after they bloom. Shortening or removal of long slender stems with no side shoots and cutting out dead wood may be done at any time.
* As needed, a fungicidal spray in the spring as the buds show color will control petal blight, a fungal disease that appears as discolored dots on the petals and quickly discolors and collapses the blossoms.

Contact Information

Carol Flowers, Secretary Phone: 202-965-5308
Email: bstelloh@mac.com

© Copyright 1999-2009 Azalea Society of America