An Unseasonable Freeze
Rudolph Henny
On the evening of November 11, a storm of great intensity that lasted three days, carried from the arctic by strong winds enveloped the Pacific Northwest and sent temperatures down to lows of from 5° to 10° F. This condition covered British Columbia, and the states of Washington, and Oregon. The season prior to this time had been mild, and damp, and hardly a light frost had occurred in any of the regions mentioned.
I am not aware that a light preparatory frost or two would have been any aid save for possibly stopping the growth of the plants, but the low temperatures in some reported instances to -5° F. were too great and the plants would have suffered serious damage in any case. Here in the Willamette Valley in Oregon the temperature low was near 7° F. and quite uniformly distributed, this was not the case in the great freeze of 1950 when temperatures varied greatly in the short distance of merely a mile or two. In discussing the results of the Questionnaire sent out by the Society on the damage of that freeze, we who sat on the committee with Dr. Clark evaluating the individual hardiness reports could only wonder at their great disparity. No doubt the reports sent back on the questionnaire were the honest observation of the member filling it out, but if the person had no accurate temperature device that measured and recorded the low he would quite naturally rely on newspaper, radio or just plain hearsay. Since that terrible cold spell was more severe it also differed in that the freeze of November 11 was much more uniform. Those gardens with an elevation of a hundred feet or some other quirk in 1950 might have escaped the bad effects, and summarily bloomed even tender species, and varieties in the ensuing spring. From all reports so far obtained this freeze of 1955 dropped the temperature to a uniform 10° F. and in many localities even five degrees colder. Portland, at the north end of the Willamette valley was plagued with a strong east wind of from 35 to 40 miles per hour that poured into the area through the Columbia Gorge. Farther North into Washington and Canada the same wind conditions existed.
The hardiness data compiled from the results of this latest freeze should present a more uniform pattern, for in this case the driving northeasterly winds carried up to the very beaches of the Pacific and this time no small sheltered spots escaped untouched by the frost.
No doubt surprises will be many and varied, and hardiness of plant and bud may not follow in patterns heretofore established. The 1950 freeze here in the Valley was devoid of any violent air movement, and the chill air encroached on the area in a calm quiet. In the November freeze the effect of the drying winds at 35 miles or more an hour surely amplified the desiccating effect that characterizes freezing and drove the chill air uniformly over the landscape. In this respect the November freeze could be classed as much more damaging.
It no doubt at this time seems precocious to mention newer and more accurate hardiness plant ratings, when the accumulated ratings gathered by the Society have not as yet been released. The volume "Rhododendrons" published by the American Rhododendron Society will be placed on sale shortly after the first of the year, and will contain important hardiness ratings based on an extremely wide survey. The editor of "Rhododendrons," Dr. J. Harold Clark, and his committee will in the months to come gather data on this latest freeze damage, and assemble another accurate strata of plant hardiness. As mentioned before in this article the uniform evenness of the November freeze will certainly catalogue plants in the 5° F. to 10° F. hardiness. The 1950 freeze showed a low of -15° F. but left a void of information relative to hardiness up to 10 F. As the hardiness report progresses the November freeze will supplement the information needed for the 0° F. to 10° F. strata. One comes to realize the number of seasonal climatic extremes necessary for compiling an accurate hardiness chart, that covers widely separated growing conditions and the number of years necessary.