Less Freeze Damage Apparent in Seattle Area
Lawrence J. Pierce, Seattle, Wash.
Early December caught most of our tender and semi-tender species and hybrids unprepared for an arctic blast. Previous fall months were mild on temperature and short on rainfall. Previously a superb summer growing period had produced a prolific bud set and much second growth. Like the November 8, 1955 early deep freeze which came without warning before plant dormancy had begun, the early December freeze of this past year came at an unpropitious time for plants were still growing - not having been previously frosted in my garden.
Elsewhere in the Pacific Northwest south of Puget Sound much lower temperatures were recorded and much more snowfall fell, causing more severe plant damage. At the Seattle-Tacoma airport, 15 miles south of Seattle, the official weather station recorded temperatures rising to 32° on only two days during the period from Dec. 4 to Dec. 12, while low temperatures ranged from 26° to 13° F. Another cold spell from Jan. 3 through Jan. 9 brought lows varying from 28° down to 15° F.
Temperatures recorded at Portage Bay, University of Washington, on Lake Washington were usually a degree or two warmer than those recorded at the airport. No wind velocity readings were obtainable but we do recall a sharp cutting N.E. wind on Dec. 8th at 20-30 mph.
Discernible damage apparently varies greatly in our Puget Sound area depending on location of gardens, air drainage, and snow coverage. Those gardens close to salt or fresh water are less damaged than similar gardens away from the Sound or Lake Washington.
In my own three-acre tract on Brace Point surrounded by salt water on three sides we have had less damage than in most other Seattle areas. On Dec. 8 we registered a low of 15° F with winds of 15-20 mph from the Northeast. Our usual prevailing winds are from the S.W. and winter temperatures average 42° F. Again on January 6 we registered a low of 17° F during a week of below freezing night temperatures. However since Jan. 10th we have had normal rainfall and degree days except for a few days in early February with NE winds and temperatures in the low 30's.
Small seedlings of hardy Sikkim Maddenii, and Formosum pinks were killed outright. All other Sikkim seedlings survived without even leaf burn. Species plants damaged by leaf scorch and/or split bark were arboreum, chapmanii, cinnabarinum, crassum, davidsonianum, grande, hodgsonii, johnstoneanum, oleifolium, sperabile, and viscidifolium.
Hybrid plants which were defoliated or had leaf scorch included 'Eldorado,' 'Lady Berry,' 'Little Gem,' 'Mariloo' and 'Ruby Hart.' It has been most difficult for us remembering past similar periods to understand why every falconeri, fictolacteum, macabeanum, mollyanum and their hybrids were not damaged as far as we can see presently. Neither were the hybrids 'Azor' and 'CIS' defoliated which disproves in part present prejudices against them.
Thankful as I am for a collection of rhododendron species and hybrids practically unharmed, I am more than thankful to have had this testing period for the many new wonderful hybrids left to us by Halfdan Lem, Letter Brandt, and Ben Nelson. These crosses most of them as yet unnamed have met a test of hardiness in my garden this winter. It remains to be seen how many will make the grade when in bloom.
Bob Badger reports from Woodinville, Wash., that maximum temperatures remained below freezing from Dec. 4 through Dec. 13, (hitting a low of 8° F) and again from Jan. 3 through Jan. 10 with the lowest temperature reaching 14°F. These temperatures were recorded on a maximum-minimum thermometer in his garden which is located 500 feet above sea level. He recorded seven days which were 32° F or below ahead of the cold snap which started on December 4.
Extreme cold damage was suffered by R. valentinianum 'Aola' probably dead; Maddenii Series seedlings, probably dead but may come back from the roots; R. scabrifolium looks very bad at this time and is probably dead.
Severe leaf burn damage is shown on R. arboreum, buds are alive; R. arboreum PI #307329 (had some protection which the above did not and damage was not as severe). R. lanigerum, buds alive; 'Fabia', buds alive; R. litiense, plant appears alive at this time; R. wiltonii x R. macabeanum seedlings are alive. 'Moonstone' x 'Nuggett' seedlings, all forms of 'Marillo', R. triflorum and R. concatenans show medium leaf burn damage. 'Ethel', R. rex and R. augustinii have slight leaf burn.
All the above plants were sitting above ground, not planted, in an open condition in containers, balled in burlap or plastic and in some cases completely without cover on the roots. These plants have been sitting in this manner since June and July of 1971. There was no snow cover for the plants during either cold snap. There was some wind accompanying the cold but no severe winds and especially not on those nights when it was the coldest temperatures.
The consensus seems to be after looking at the plants in the garden that very few plants were lost completely and most of the damage is leaf burn and in some cases flower bud loss. In spite of the severe weather which the plants were subjected to, a plant of R. moupinense, pink form is starting to bloom at this time (January 17) with no brown flower pips.