Azalea Blossom Watch
APRIL 11, 2014
Spring has finally sprung! The cherries and daffodils are currently in full bloom, roughly 10 days behind usual. The cold temperatures experienced in the mid-Atlantic region this winter put us back into a solid zone 7 (average night time low of 0-10 degrees F). This year, marginally-hardy plants that might have wintered fine for the past 5 years, may have suffered winter burn, bud blast, bark splitting or they might have perished altogether. We lost a hardy gardenia.
The Azalea Collection has had few casualties – the damage most seen is leaf scorch from winter cold and wind. Cultivars with Rhododendron indicum, (a zone 8 species used in breeding for evergreen foliage, large flowers and late blooming properties) as a parent are showing some damage to the foliage. Most of them survived and will grow it out. Cultivars using R. kaempferi (a zone 5 species used to instill hardiness, early blooms, color ranges and height) as a parent are almost deciduous this year but their flower buds are intact and ready to bloom in just a few weeks. This includes many of our Glenn Dale azaleas. Species using R. poukhanense (a zone 6-7 species used for larger flowers, the lavender colors, foliage and lower growth habit) also appear to be deciduous this year. Rhododendrons with larger evergreen leaves may have winter burn in the form of leaf scorch. The damaged leaves will drop off in June as the new foliage emerges.
Yesterday while working on the southern side of the Glenn Dale Azalea Hillside, I detected the first signs of bud color. We are about 10 days behind our normal average for bloom. I expect our peak bloom weekend to be at the end of April to early May.
Happy Spring, everybody! See you in the garden!
Barbara Bullock, Curator of Azaleas & Rhododendrons
U. S. National Arboretum