Early plant growers, beware of freezing temperatures

Everyone has enjoyed this winter with record-breaking warm temperatures and little snow. With temperatures rising in 60s and 70s, I am reminded by the Lowe’s commercial of the guy being drawn out of his bed and through the wind into his yard. I usually can gauge this period by the increase in phone calls on various yard care questions. It is exciting to see tree and shrub start to leaf out and daffodils ready to bloom.

Reality can be a bucket of cold water because we need to realize we are still in zones 3 and 4 and this is an abnormal year. Not that we shouldn’t enjoy it but beware a frost or cold weather could still be out there yet this spring. As long as the buds were still protected from freezing they were OK but once they start to grow, tender shoots can be easily injured or damaged by frost. Even nonfreezing temperatures may cause a chilling effect.

When temperatures cool down below the freezing mark, water molecules form ice crystals between the cells in the leaf and young stem. In a freeze-drying action, water is drawn from the cell and dehydration can occur and injury. Injury may vary due to slight variation of air temperature within the tree. It is common to see only the buds on lower parts of the tree die and the rest of the tree to leaf out normally.

Frost injury can cause the dieback of new stem growth and also injure flower buds of early flowering trees and plants. Flower buds or forced flowers will reduce or prevent fruit production or may cause malformation if only partial fertilization occurs.

Borderline tree species are most susceptible for severe injury and dieback. These species are not fully adapted to our short growing season and more adapted to a warmer climate. They can break bud if planted in a warm sunny spot and start ahead of the more adapted species. An example is the Norway maple which can survive most of our winters but just the right spring conditions and a heavy frost can kill one-third or more of the canopy.

Most hardy native trees such as elms are not normally affected. Recent temperatures have caused many of these species to leaf out. The leaf is exposed to the same chances of frost injury as the borderline hardy tree. Other environmental events such as wind, rain and cloud cover all help to lessen the severity of frost damage. Radiant heat given off by nearby buildings or larger trees can reduce the effects of frost. One maintenance tip is to refrain from fertilizing trees and shrubs until after mid-May. Excess nitrogen fertilizer will push more tender growth that is more susceptible to a freeze.

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