Azaleas and Rhododendrons

In honor of my visit to Magnolia Plantation and Middleton Place in Charleston, South Carolina, here's a primer on these spring-blooming beauties.

All azaleas are rhododendrons, but all rhododendrons are not azaleas. Got that? Me neither. There might be 50 Rhododendron species or 1500, depending on who's counting, and probably another eight thousand recognized hybrids. Although botanical study has proven that they are in the same genus, there are some basic differences:

Rhododendrons have:

Large, broad, long and leathery leaves
Large, bell shaped flowers at the ends of the branches
Flowers with 10 or more stamens
Thick, sometimes gnarled branches

Azaleas have:

Small, narrow and pointed leaves
Small hairs on the underside of the leaves, especially along the midrib
Flowers with five lobes along the sides and on the tips of the stems
Flowers with five stamens
Brittle, twiggy branches

The first rhododendron species were introduced in 1653. The bulk of new introductions occurred in the early 20^th century. Plant collectors mounted daring expeditions in search of new varieties in Asia and the Himalayas. They returned with a wealth of materials to use in hybridizing: for color, cold hardiness and pure fun, judging from the thousands of hybrids available. Some hybrid names give away their size or color, like Pink Whalloper, Cotton Candy or King of Shrubs; some are named after pretty girls, like Cynthia or Gigi; some sound just plain silly, like Faggetter’s Favourite or Halfdan Lem.

By contrast, azaleas were first mentioned in Japanese poetry in 759 A.D. The Japanese have a revered place for these beautiful plants in their gardens, thought and lore. Azaleas too have been hybridized, bringing us a kaleidoscope of colors from which to choose. Some bloom so abundantly that blossoms completely hide the foliage. Several different colored plants together can create what appears to be a multi colored shrub.

Deciduous azaleas drop all of their leaves in the fall. All native North American azaleas are deciduous. In dry weather, they may drop their leaves earlier than usual. Their leaves then grow back in the spring.
 

Evergreen azaleas, most native to Asia, also drop their leaves. They appear to be evergreen because they grow two sets of leaves each year. Their spring leaves are thinner, larger, and grow along the stems. These leaves drop off in the fall. Their summer leaves are thicker, smaller, grow crowded at the branch ends, and can remain on the plant through a mild winter.

Azaleas and rhododendrons, like many other plants, are classified as being species or hybrids. A species is a group of plants that interbreeds and is reproductively isolated from other groups. Seedlings from such isolated species populations look like the parents, or "grow true from seed". Hybrids, on the other hand, are crosses between other species or hybrids. Hybrids can only be faithfully reproduced from cuttings, which are clones of the mother plant. Hybrids, if they set seed at all, will not grow true – one can never be sure what the seedling of a hybrid will look like.

Now, imagine a perfect spring day. The forsythia and daffodils give long-awaited sparkle to the freshly greened landscape. Could any sight be more refreshing after a dreary winter? Nope, you think, it’s a beautiful sight. Well let me make one suggestion – Huge balls of lavender flowers nestled in shiny canoe shaped leaves. The light-purple flowers of a ‘PJM Victor’ rhododendron blooming with the daffodils and forsythia create the perfect spring palette.
 

“Since its origination, ‘PJM’ has become the standard by which all small, broad-leaved, cold hardy rhododendrons are judged”, according to Michael Dirr, author of Dirr’s Hardy Trees and Shrubs. “The initials P.J.M. stand for Peter J. Mezitt, who began the process completed by his son Ed in developing the very first crosses ever to carry those initials. The first field of ‘PJM’ was developed from 1936 to 1945 in Massachusetts, and Ed Mezitt's bushes have been the basis of many of the most popular cold-hardy varieties ever since.”

'PJM' is not a single cultivar, but a group of hybrids derived from a particular cross performed by the Mezitts. The resulting ‘PJM’ cultivars vary in habit, foliage color, flower color, bloom time and growth rate. ‘Victor’ is compact, with early lavender flowers. ‘Olga’ is bright pink and blooms in late spring. These plants are among the hardiest and most reliable evergreen rhododendrons.

"We had all but forgotten this hybrid,” says Ed Mezitt, “until one Sunday in early May in 1945. We were just developing our nursery in Hopkinton, Massachusetts, and we were visiting it that morning, having been tied up during the busy season in our Weston nursery most of the week. My heart still skips a beat when I recall the reaction of our entire family when we saw that ribbon of brilliant pink running across the hill. My Dad was so enthusiastic about these little dwarf plants - only six to eight inches tall — in full bloom, that he immediately made the remark that this was the most spectacular rhododendron of our time. We named it ‘P.J.M.’ right on the spot and those of us who knew him can see the vigor, excitement and showmanship he possessed perfectly reflected in this plant."

If April is yellow and purple, May is pink and white. Of the seeming millions from which to choose for flowers in May, one that is unique in shape and stature is the Korean Azalea. It blooms reliably in my parent’s garden on May 1, my wedding anniversary. For 15 years they’ve called it the “Anniversary Bush”. The Korean Azalea is elusive, but it can be ordered from specialty nurseries or catalogs. It also goes by the name Royal Azalea, but I’m sure you won’t find it listed in any catalog as the Anniversary Bush.

The Korean Azalea (R. schlippenbachii) is named for Baron Alexander von Schlippenbach, a Russian naval officer who collected plants in Korea and discovered it in 1854. The Arnold Arboretum of Harvard University, the oldest public arboretum in America, first introduced it to the United States in 1905. The Royal Horticultural Society awarded the Korean Azalea the Award of Garden Merit in 1993.

Michael Dirr calls it “possibly the most handsome of all azaleas when the soft pink, fragrant flowers cover the shrub in May”. I have to agree. The fragrant flowers, in white to tender pink or rose, open with or even before the rich bronze spring foliage. The leaves are distinctive and appear in whorls of five. They change to a deep orange color before dropping in the fall. This azalea is native to open woods in Korea and northeastern Manchuria. Mature plants are commonly four or five feet high in the garden. My parents have two that are over eight feet tall and five feet wide. That’s what happens when a shrub is happy in the same spot for 35 years.

Azaleas and rhododendrons like acid soil and light shade. They will thrive at the edge of a woodland area where the sunlight is dappled throughout the day and the soil is moist but not wet. They are also prime candidates for a mixed border with trees, other shrubs, and perennials, and they do a nice job disguising foundations and utilities. Plant azaleas and rhododendrons in spring, after the last frost date. Or, wait until early fall, the other perfect planting time for shrubs, in order to enjoy a glorious flowering tapestry next spring.