Regional Gardening Reports :: National Gardening Association

In the Garden:
Upper South
May, 2007
Regional Report

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The intense colors of deciduous azaleas add a brilliant note to the garden in May and June.

A Brilliant Burst of Color

Garden writers may extol the virtues of choosing plants with multiple seasons of interest, but sometimes you grow something that is so spectacular, though only briefly, that you just have to include it in your garden. For me, near the top of that list are deciduous azaleas.

Certainly, evergreen rhododendrons and azaleas are beautiful and have the advantage of year-round foliage, but once you've seen the brilliant red, orange, yellow, peach, or white flowers of a deciduous azalea, most likely you'll be smitten, too. Plus, these azaleas are much hardier than most of their evergreen relatives. Many gardeners also feel that they're easier to grow.

Although there are individual species of the genus Rhododendron that are deciduous, those grown most widely in the garden are hybrids created from various crosses of R. molle (a Japanese species), R. calendulaceum (U.S. native flame azalea), R. occidentale (native to western U.S.), and R. arborescens eastern U.S. sweet azalea). Generally, these hybrid deciduous azaleas grow 6 to 10 feet tall and 4 to 8 feet wide, but there are also a few with a dwarf, spreading growth habit. Blooming during May and June, most begin to flower when young, with blooms that are pleasantly fragrant. An added bonus is fall foliage color of yellow, orange, or red. Most are hardy to at least -15 degrees F, but some are hardy down to -45 degrees. All grow well in sun or part shade.

A Little History
With the mention of deciduous azaleas, most aficionados envision the Knap Hill and Exbury azaleas. The Knap Hill group originated with Anthony Waterer about 1870 at Knap Hill Nursery in England. Some examples include 'Coronation Lady', with salmon-pink and orange-yellow flowers; 'Debutante', with carmine-pink flowers blotched with orange; or the appropriately named 'Orangeade'.

Later, in the 20th century, Lionel de Rothschild at Exbury Estate expanded the hybrid selections. Some you might see include red 'Balzac' or 'Royal Command', pink 'Cecile' or 'Pink Delight', double yellow 'Cheerful Giant' or 'Double Delight', orange 'Gibraltar', or golden 'Old Gold'.

Over the years, others have worked on developing deciduous hybrids. Ivan and Robertha Arneson of Portland, Oregon, began hybridizing azaleas in 1959, making over a hundred crosses each year and selling up to 20,000 seedlings each year. Some named varieties developed by them include the orange-red, large-flowered 'Arneson's Flame'; 'Arneson's Golden Soitaire' with lemon-yellow flowers blushed with red, orange, and pink; 'Arneson Ruby' with true-red flowers; 'Arneson Cameo' with single deep-pink flowers with an orange-yellow blotch; and 'Arneson Gem' with golden flowers edged in brightly glowing orange.

The Mezitt family of Weston Nurseries in Massachusetts, famous for the PJM rhododendrons, focused on creating summer-flowering deciduous azaleas, extending the blooming season into late July and even early August. Also included in their goals was resistance to mildew and brilliant fall color. Their plants were tested under adverse conditions, including full sun, exposed hillsides, and rocky, clay soil. The dusty red 'Millenium' is one example. 'Pink and Sweet' has purple-pink flowers with a golden flare in the throat.

For hardiness, no deciduous azalea can compare with the Northern Lights series from the University of Minnesota Landscape Arboretum. Any azalea released and included in this series has a bud hardiness of -30 to -45 degrees F. The "Lights" are derived from crosses between R. x kosteranum (the Mollis hybrid group), R. prinophyllum (our native roseshell azalea), and others. Usually, they have fragrant flowers in shades of pink, white, or yellow and grow to a height and width of 6 to 8 feet or more. Among the named varieties are 'Pink Lights', 'Rosy Lights', 'White Lights', 'Spicy Lights', 'Orchid Lights', 'Golden Lights', 'Lemon Lights', and 'Northern Hi-Lights'.

For something out of the ordinary, consider the one that Dick Cavender of Portland, Oregon, has developed from R. arborescens and R. prunifolium that blooms in September and October with bright, flame-orange flowers amidst its red fall foliage. Although local nurseries usually offer some deciduous hybrid azaleas, one of the best mail-order sources for this one and others is Greer Gardens in Oregon (

Growing Azaleas
Since azaleas grow naturally in wooded areas in well-drained, acidic soils high in organic matter, the best suggestion is to mimic these conditions as much as possible. Test the soil acidity to determine if adding sulfur to the soil is necessary. In addition, add organic matter such as leaf compost or peat moss to the top 12 inches of soil. Ideally, the soil is well drained, since standing in water, even for a short period can lead to root rot. If the drainage is poor, consider growing deciduous azaleas in raised beds. You'll get more flowers in full sun, but azaleas grown in light shade require less water.

Azaleas are shallow-rooted plants, so using hardwood mulch is recommended. In times of dry weather, watering may be necessary. Be careful to avoid hoeing or digging beneath the plants. Feed deciduous azaleas every year with a water-soluble, acidic fertilizer. Since plants produce flower buds in the summer or fall of the previous year, prune right after blooming.

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