Winter Damage in the Chicago Area
Eldred Green, Chicago, Illinois
Winter damage in the Chicago region was extremely severe last year. Roses were frozen back to the ground line and many other plants injured. Flower buds on flowering dogwood were killed and the buds on such iron-clad rhododendrons and azaleas as R. canadense and R. poukhanense suffered damage above the snow line. R. mucronulatum, its pink form, and Gable's hybrid 'Pioneer' lost their buds. Needless to say this damage extended to the evergreen azaleas.
Now this was not a cold winter, as Midwest winters go. The official temperature went to -11° but this is often a few degrees higher than in the outlying areas. There was only one cold spell of this severity, in early January.
Obviously it was not the low temperature that caused damage. Many of the injured plants had survived temperatures that went into the -20's in previous years. Plants protected by Rose Kones were not injured in some places, injured in others. (Rose Kones are about ⅜" thick of white expanded plastic. They are placed over plants in the fall and keep sun and wind off them. They do not keep out cold but slow clown fluctuations caused by bright sun.)
The winter was thought to be a little more windy than usual and possibly drier as there was not much snow. It is possible that the winter injury was due to prolonged dry air and wind rather than cold. The plants went into the winter in good condition. The late summer was dry and caused good maturing of the plants. There were fall rains that wet the soil so that there was not root drought in the winter.
One theory advanced was that the fall rains may have softened the plants so that they were more susceptible to winter injury than if they had been in a drier condition. However, the fact that protection from sun and wind, as with the Rose Kones, did prevent damage would indicate that more than cold injury was involved.
The theory of damage by sun is ruled out by damage that occurred to plants that received no direct sun at all. The theory of dry air is upset by damage that occurred to plants under protected conditions where there was no dryness. The breaking of dormancy, due to a damp fall following a drought, falls down when injury was found on plants that had been watered regularly and were not affected by the relatively mild drought that occurred in late summer.
The vagaries of the winter were noticed when injury was found on a variety in one garden that was uninjured in another. There was wide-spread winter injury to many other plants as well as to rhododendrons and azaleas. Winter protection that was effective in one garden was ineffective in another. No definite pattern can be found. Varieties severely injured in one spot were unharmed in others.
Whatever caused the severe winter injury, which was described by one gardener as the worst in 18 years, is a puzzle. No one factor seems to be the dominant one. There were no great extremes. In fact most people considered the winter a rather mild one. There were no late frosts that had been a bother for some years. In any case we had a very bad winter for plants and the cause of it is puzzling the experts. Perhaps the best answer is that it was a succession, or combination, of many little things which were not harmful in themselves but which exerted a cumulative effect on the plants. Certainly nothing else seems to fit.