Major stresses such as insects, disease, poor nutrition, and insufficient water levels during the growing season can weaken plants going into winter and thus reduce their survival. On the plus side, full-grown trees often need a couple of years of drought or flooding to kill them off. Being mindful of providing for basic plant needs helps.
It’s important to know that winter damage can occur in shades of grey. It’s not always life or death. The best time to assess partial winter damage is when plants are budding out or blooming in the spring. Partly damaged plants will bud out or bloom unevenly. If conditions are not corrected, eventually the whole plant could die. So take partial winterkill as a warning sign. Shrubs often have a pattern of lower branches growing first, followed by upper branches. That’s not winter damage: just sap getting to the lower branches faster. Partial winter damage can be in the roots or stems. Branches can’t grow if the roots that normally feed them are dead. This can result in some branches growing a couple weeks later than others, or some may start growing and then simply die. Often this can mislead one to think some disease is attacking the plant. Plants have some capacity to repair these partially damaged branches, but if there are too many of them it would be a good idea to prune out a lot of them. If you are getting partial winter damage, reflect on whether it might be your fault or just a consequence of naturally occurring weather.
When looking at partial winter damage, don't forget to look at the base of the plants. Voles or mice may have been chewing away at trunks or stems. In that case, you need to consider pest control. While mice and voles tend to stay under the snow and cause damage at the base, rabbits will stay on top of the snow and can cause damage further up. One can purchase tree wraps that will protect tree trunks. For bushes, one may need traps or poisons. Some repellent sprays can be used on trees and shrubs, but I don't have much experience with those to determine if they are worthwhile. One can also buy metal mesh to wrap around the base of plants such as a small cylinder or mini fence that can exclude some rodents.
A plant’s first winter in your yard may not be a true reflection of its winter hardiness potential. When you buy a plant from the nursery, it may not be in sync with the growing season. Greenhouse nurseries may start plants in February or March so they will be bigger when you purchase them in May. Those plants may go dormant in midsummer and then “wake up” in fall. Also, if the plant was propagated during the summer, it may still want to grow into the fall. Some plant species are more prone to partial dieback after the first winter. We almost always have some tip kill on newly planted small sour cherries the first year, but after that they are fine.
Slowing wind is important. Wind can cause physical damage by branches rubbing together too much in winter. Wind can also dehydrate branches or bark. In cities and suburbs there often are fences and buildings which greatly slow down wind. But sometimes, buildings or fences may be situated in such a way that the prevailing wind gets accelerated. If you know of spots that are wind tunnels, avoid them. If you live in the country, you'd want to reduce wind by establishing shelterbelts against prevailing winds - which for the prairies is usually from the northwest side.
Bob Bors, recently retired from the University of Saskatchewan, is the co-author of 'Growing Fruit in Northern Gardens'.
This column is provided courtesy of the Saskatchewan Perennial Society (SPS; [email protected]). Check out our website (www.saskperennial.ca) or Facebook page (www.facebook.com/saskperennial).
