April 2015 in the Garden

We’re well on the way to one of the warmest springs in recent memory. A number of plants flowered three to four weeks early and many familiar April-blooming plants long since put out their flowers (what a February and March!). But there are plenty of plants sitting tight, waiting to flower as they normally would—or at least within only a week or two of their usual time. On this list of conservative bloomers are many in the genus Rhododendron. We can expect a lot in April from this group, and with around four hundred and fifty different rhodos in the Garden, that’s a pretty impressive group.

Cultivated, temperate rhododendrons fit more or less into four main groups: deciduous and evergreen azaleas, lepidote (scaly-leaved) rhododendrons and elepidote (non-scaly-leaved) rhododendrons. The elepidotes, being the most familiar to garden visitors, will be magnificent in April as usual, but the subject of another article. Azaleas are not the smallest rhododendrons—though many are dwarfs—but they often have smallish leaves, and they produce their flowers in a slightly different way than do “conventional” rhododendrons. Rhododendron indicum (florist’s azalea) has some of the largest flowers of any azalea, and there are plantings of several old Japanese selections in David C. Lam Asian Garden along Fortune Trail. These were renovated (cut back hard) a few years ago to allow for more movement on the trail, and are now fully recovered and fat with flower buds. Nearby to the west along Fortune Trail at about the same time you can see the classic Japanese deciduous azalea, R. molle with its striking burnt orange flowers.

Among the lepidote rhododendrons, which are not only scaly, but often pleasantly aromatic as well, there is considerable choice. In the E.H. Lohbrunner Alpine Garden, the small blues, R. impeditum, R. russatum and R. fastigiatum are all worth a look. None of them produces actually blue flowers—they are all shades of purple, but they (and their close relatives) are the closest thing to blue in the rhododendron world. They are all planted with a modicum of shade and where soil drainage is excellent, as this is a definite requirement for these high altitude species from southwestern China, where steep, rocky ground and cooling fogs are usually the order of the day. In the Asian Garden, the extra shade from the high canopy of conifers makes growing these diminutive rhododendrons somewhat more challenging, mostly because of competition from overly vigorous shade-adapted plants, but there are plenty of other lepidotes that do well here. The top of the list for April flowers is probably R. augustinii, with its willowy upright stems, narrow, diamond-shaped leaves and fabulous purple “blue” flowers. However, the closely related and similar looking R. concinnum (maroon-violet flowers), R. davidsonianum(pink flowers) and R. rigidum (white, pink or lavender flowers with a bronze to raspberry throat flash) all give the Augustine rhododendron a serious run for its money. Just because the magnolias and camellias were early, doesn’t mean April won’t be worth a visit!

To view examples of the plants mentioned visit our Forums.

Article submitted by Douglas Justice, Associate Director, Horticulture and Collections, March 31, 2015. Forum photos posted by Wendy Cutler.

Leave a Reply