Rhododendrons are a great plant to add winter interest to any garden. Using small leafed rhododendron is more unique way of designing rather than use the larger leafed types.
Rhododendron shrubs like acidic soil that is well-drained and rich. The roots are shallow and fibrous and the soil must not be very wet or very dry. The ph of the soil should be 5.5 or less. If you have soil that is not acidic you can add sulfur or iron sulfate to lower the ph have your soil tested so you know how much to add.
There are hundreds of varieties of Rhododendron and Azalea. Azalea is the name commonly used for native deciduous species and some evergreen Oriental types. There is no hard and fast rule however for calling these types of plants azalea or rhododendron.
There are many beautiful rhododendrons. However, some are not reliably cold hardy or heat tolerant in our area. In general, more varieties may be grown in milder climates.
Of the many hybrids available, those derived from Rhododendron catawbiense, called Catawba hybrids, have the greatest hardiness. You should experiment carefully with newer varieties that are not tried and true for your zone.
Soft lilac fading to white, late flowering, a R. maximum hybrid.
White with a lavender tinge later fading to white.
Dark red with a ball-shaped flower cluster. Broad, bushy plant.
Red with purple markings. Hardy.
•Boule de Neige
White, early. Slow growing, but develops compact, large plant.
White flowers in round trusses. Narrow leaves, tall, vigorous.
Purplish-pink with green markings. Hardy.
Deep purplish pink with red markings.
•Mrs. Chas. S. Sargent
Deep rose spotted with yellow. Cold hardy.
Red flowers similar to America. Cold and heat tolerant.
Very deep violet purple with darker blotch. Very hardy.
Lavender-pink flowers produced early in spring. Evergreen leaves small, turn purple in fall. Very hardy.
Lavender pink with green markings. Endures temperature extremes. Best for beginner.
Most popular of the evergreen azaleas are the Kurume hybrids. They are popular for forcing in pots and for planting outdoors. In the southern United States, they become large, showy shrubs in the spring. They are fairly slow-growing plants with dense, twiggy growth. Hardiness varies considerably among the many varieties. Here are some of the hardiest.
Flowers are hose-in-hose (one blossom inside another), which gives the effect of semi-double flowers. Vivid pink color. Poor exposure will cause leaf scorch and twig die-back.
Vivid red flowers on a low, cushiony plant. One of the most hardy.
Variety from which Hino-crimson was selected. Very similar but color not as intense red.
Large, hose-in-hose, soft pink flowers. Plant is low and spreading.
Large, single white flowers. Most reliable of white flowered Kurumes.
Girard hybrids are a fairly recent introduction among evergreen azaleas suitable for colder climates. Their growth habits vary with variety, but generally most are fairly low and bushy. Leaves are bright green and some develop a reddish fall color. Although some older leaves may drop in the fall, leaf retention is greater than that of the Gable hybrids. Flowers are primarily single, but fairly large. There are many fairly hardy varieties in this group. Here are a few distinctive varieties to consider.
•Girard Hot Shot
Large flowers in a deep orange-red to scarlet. Plants develop an orange-red leaf color in the fall for winter color.
•Girard Renee Michelle
Flowers in a clear pink and large and showy. A very cold-hardy variety.
•Girard Sandra Ann
Large purple ruffled flowers make this a distinctive variety. Plants are more upright than some Girard varieties.
Deciduous azalea varieties are as follows.
•Exbury (Knapp Hill) hybrids
Becoming extremely popular. Many varieties have good hardiness. Available in pastel shades ranging from cream, through pink to yellow and orange. Currently the favorite deciduous azaleas.
•Northern Lights hybrids
Developed at the University of Minnesota Landscape Arboretum for winter hardiness. Plants and flower buds are said to have survived -40 degrees Fahrenheit. Plants are fairly compact and can grow to about 6 feet in height and width. Some suitable varieties are Orchid Lights, Rosy Lights, Spicy Lights, Northern Lights and White Lights.
•Royal azalea (R. schlippenbachii)
A reliably hardy azalea with large, fragrant rose-pink flowers. Foliage has good autumn color, although may sometimes be burned by late summer heat.
•Korean azalea (R. poukhanense)
Lilac-purple. Deciduous in cold climates. Low, spreading. One of the hardiest azaleas available. Early.
Not as hardy as Exbury, but much many varieties. Colors mainly in yellow, apricot, orange, red.
Available in a wide range of colors. Exbury hybrids are an improvement of the older Ghent hybrids.