Now that we are past some of the winter enjoyments of sledding, skiing, making snow forts and viewing the picturesque scenery out our windows, we can start looking forward to spring. The ice, the salt, the mounds of hard snow piled high and the branches scattered on the lawn from the strong winter winds, these are the obvious signs of a hard winter. The less obvious signs of winter show up in the spring.
Different degrees of winter kill will be noticed in the spring as trees and shrubs begin to break dormancy and the tender leaf and flower buds emerge.
Damage from a hard winter can be seen in flower buds; flower buds that form fruit, leaf buds, branch dieback and plant vigor. Winter kill can be partial where the plant will recover to severe where the plant dies. A hard winter with any combination of extremely low temperatures, strong dry winds or low soil moisture levels can result in plant tissue damage.
Flower buds on spring blooming trees and shrubs form in the fall and remain dormant until spring. If a plant is stressed due to summer or fall drought, the flower buds can be sparse or weak. A hard winter can kill more of these buds resulting in a light bloom and sparse fruit set the following spring.
Leaf buds are formed in the late fall. In most cases they are tougher than the flower buds and can withstand normal winter conditions. Partial winter kill to leaf buds appears as deformed leaves or leaves that are smaller than normal. In the spring the new growth can struggle to emerge resulting in later than normal leaf emergence or smaller, weaker leaves than normal. Total winter kill would be no leaves emerging in the spring with the possibility of twig or branch dieback. In a sense, the tree or shrub has been pruned by the nature of winter.
Severe winter damage can result in total death. Branches are dark brown or black and brittle, snapping off when all green life is gone. The root system may have some life left but not enough energy to bring dead branches back to life.
Evergreen type plants like rhododendrons, boxwoods, holly and conifers can suffer from winter burn to the foliage on the side which is most exposed to the extreme winter winds. Needles of conifers like pine, firs, arborvitae, and yews will turn yellow with some damage and brown or black if totally dead. These damaged needles will fall off leaving the tree thin and sparse.
Plants that are tender or in an area with strong winter winds will need some protection. This can be in the form of a burlap fence or a physical wind break. Never use plastic bags, which can suffocate the plant. Snow carefully shoveled over smaller plants will insulate the plant against subzero temperatures and slow the desiccation process.
Japanese Maples have become popular and more affordable in the last decade. The fine foliage and beautiful red leaf tones make them a focal point in any landscape. The problem is they are borderline winter hardy in this area. At the Arboretum we have several spectacular specimens growing in semi-protected areas on the grounds. David Horst, the Arboretum Horticulturist, checks every spring on damage to the maples around the Arboretum. In the spring he will wait for the new growth to emerge before he prunes off winterkill branches.
The warm weather at the end of February did get some sap flowing but the trees seem to understand that old man winter can still blow in and blanket the ground with a late snow. We cannot rush Mother Nature. Our last frost date for this area is around May 10.
Margo Hansen is a horticulturalist and Director of Programs at the Bickelhaupt Arboretum.