QBARS - v19n2 Winter Damage at University of Washington Arboretum

Winter Damage at the University of Washington Arboretum
J. A. Witt, Seattle, Wash.

In assessing winter injury to plants it is always well to establish the conditions that caused the damage. The cold that we experienced in mid-December 1964, was very well defined. The maximum temperature on the 14th was 40° F, the minimum 32° F; the maximum on the 15th was 32° F, the minimum, 11° F. The next two days had maximums of 16° F and 25° F and minimums of 13° F and 17° F respectively. The temperature rose slowly after that, with maximums in the high thirties or low forties and minimums at slightly above or slightly below freezing. The Arboretum's thermometer is in a screened box and the temperatures recorded probably are comparable to those in our lath house. The intense cold was accompanied by a very desiccating north wind.
The damage to the Arboretum's Rhododendron collections was not as severe as it might have been, although certain species and clones suffered badly and a few were probably killed, at least to the ground. At this writing (3/25/65) it is still too early to determine which are actually dead and which will eventually make a recovery. We learned in 1955 not to be too hasty in removing a seemingly dead plant.
Below are three lists of (1) plants very badly damaged, dead or killed to the ground; (2) plants with moderate leaf or bud injury; (3) plants with minor leaf injury or none at all despite a reputation for tenderness.