QBARS - v22n1 Rhododendrons After a Hot, Dry Summer in Washington, D.C.

Rhododendrons After A Hot, Dry Summer In Washington, D.C.
George W. Ring, Fairfax, Va.

This is a report on observations of the flower bud set, general vigor and foliage density of more than 250 varieties and species rhododendrons at the U.S. National Arboretum in Washington, D.C. The observations were made in February, 1967 following the hot and dry summer of 1966 during which the temperature reached 90° F, or higher, on more than 50 days. Precipitation during the 3-month period June-July-August was only 4.6 inches compared to a normal of 12.3 inches.
The original intent of the observations was to acquaint the author (a recent enthusiast) with many of the clones already developed by breeders; and to identify those having good flower bud set, vigor, and dense foliage for potential use in breeding new rhododendrons suitable for landscape plantings by the average non-specialist in the Washington, D.C. area.
At the Arboretum, rhododendrons have been established in three different areas. Area 1 has chiefly a southeastern exposure with the least shade of the three. A few of the plants, located on severely hot-dry slopes in this area, were omitted from the observations. Areas 2 and 3 are on a well wooded north-eastern slope. Area 2 is a semi-formal setting of Shammarello hybrids. The largest group of plants is in Area 3 along or near footpaths.
A generalized rating system (legend given below) was used in an attempt to evaluate and classify the visible wide differences in flower bud set, vigor and foliage density. Ratings for the plants in the three areas are presented on the following pages.