Frost Damage

By: John Degroot

April 14 2012

Frost Damage - Garden Clippings for April 14, 2012

                What are we talking about more than the Maple Leafs, more than the price of gas, and more than politics?  That would be the weather.

                All of us, except for ski resort owners and those involved in the snowmobile industry have enjoyed the unusually warm weather this winter.

                    Gardeners and farmers are taking the mild weather in stride.  We’re enjoying the sunshine and warm temperatures, but we are waiting with baited breath to see how plants and trees might be affected by the early spring growth.

                My Star Magnolia is not smiling.  Its flowers came out a few weeks ago, but one day later, after an overnight frost, all the white petals turned brown.  My Saucer Magnolia, whose flower buds usually open a few days later, looks only marginally better.

                  So far, it appears as if little else in my home garden has been negatively affected by the weather.  Others are not so lucky.  A week or two ago, when visiting a backyard in Wyoming, I noticed a Black Walnut tree whose tiny new leaves have turned black with the frost.  I have noticed several other trees and shrubs that are suffering the same fate.

                Mother Nature has a crafty way of dealing with frost.  My Magnolia will surely manage.  The petals are damaged, but the tree itself will be just fine.  I will have to wait till next year to enjoy its blooms.  I won’t worry about other trees that are damaged because they are equipped with enough strength to produce a new set of buds and leaves which will undoubtedly appear in due time.

                As for the other plants and trees that are producing leaves in my backyard and in gardens everywhere, I am hoping we won’t get a severe frost.  For Sarnia Lambton, the frost free date is yet a month away, and we can only hope that temperatures remain cool, but without a killer frost.

                Other than temperature, what are the factors that may affect the extent of frost damage?  Humidity, length of exposure and speed at which the cold temperature was reached may influence the severity of frost damage.

                What can be done to minimize the potential for frost damage?  If the plants that need to be protected are few and small, covering with sheets or tarps when overnight frost is expected will probably do the trick.  Misting the plants in the evening just before frost arrives will increase moister levels to help the cause.  Another light shower early in the morning before the sun rises will help remove frost.

                  Will temperatures falling below 0 degrees Celsius automatically cause leaves to freeze?  Not necessarily.  In addition to water, plants contain protein and sugars which don’t freeze as readily as water.  Plants such as Impatiens that contain higher percentages of water are more susceptible.

                What causes plant tissue to become damaged with frost?  Moisture in plant tissue forms ice crystals that puncture the walls of plant cells.  When temperatures increase, the ice crystals melt and the cell contents leak out, causing the frozen plant leaves to become limp and take on a mushy, dark, watery appearance.