Fall Frosts

Helping your garden survive a fall frost

Predicting frost is a difficult thing. Cold air is heavier than warm air, so it settles into low lying areas. Within a neighborhood or even a single property, some areas may be frosted, and others untouched. Areas under trees and near the house gain a few degrees “extra” protection. Some areas throughout Massachusetts are in a “frost pocket” and get early fall frosts seemingly the first of anywhere. They’ll sometimes get a frost three weeks earlier than even a mile away. So trying to predict frost for an area ranging from the cold pockets of Barre, for instance, to the relative warmth of Worcester is very difficult. Experience will teach you where you fall within this frost continuum. Keep your ear on the weather forecast on chilly clear autumn days. We recommend www.weather.gov  for a non-sensationalized weather forecast. Just type in your zip in the upper left box. It will also give frost and freeze warnings and advisories.

There are a couple of things which you can do to protect your plants when a frost is predicted.

• Moist soils will help plants stay warmer. If you have an early warning, water the areas thoroughly before evening. The soil will release warmth and moisture around your plants during the night, keep the air a little bit warmer.
• Cover the plants to keep the warmth from the ground in. Drape a sheet of newspaper, a bed sheet, cardboard, plastic sheets or any similar material (the thicker the material, the more protection). Do this in late afternoon for best effect. By dark much of the soil’s warmth has been lost already. Remove the covers in the morning, once the frost has left. This will prevent the plants from overheating during the day.

Tender vegetables such as tomatoes, peppers, the “creepy-crawlies” (squash, pumpkins, etc.) and others may be frost damaged. The same hold true of annuals such as impatiens, begonias, marigolds, etc. Most perennials are relatively untouched by a light frost. One notable exception is hosta, which can sustain leaf damage, but it will only harm the appearance. If we get a hard frost, also known as a killing frost, other plants will need to be protected to keep them attractive for longer. This last group includes most notable garden mums.