I’m guilty — and probably so are you — of selecting plants for our landscape that we know to either be not hardy when cold weather arrives or marginally hardy, meaning that plants can survive except when unusually cold periods occur that last for more than a day or so.

A lack of cold hardiness strongly suggests that if these borderline plants are to survive our winters, they must be given some type of protection from low temperatures. For plants that are not considered valuable specimens or for plants that are not family heirlooms, loss of such plants may not be a concern and likely they can be replaced when winter is over.

But regardless of the value of a plant, it was selected for your landscape for a reason, and it may not be as easy to replace as you might think. Thus, it is usually well worth the effort and expense to provide it with some level of protection when we know in advance that some critically cold weather is expected to arrive in the area.

There are basically two types of cold damage that our plants experience — frost damage and freeze damage. How we manage these two problems will differ somewhat.

Frost damage is a type of injury which results from radiational cooling. In this process, the air temperatures at the earth’s surface try to equalize with those in outer space that obviously are much colder.

Preventing this kind of damage to plants is quite simple. All that is necessary is to place some kind of cover over the plant to block a direct path from the ground to outer space. Most of the time this constitutes adequate protection.

Coverings can range from bed sheets to newspapers, to sheets of plastic to tarps, etc. The kicker is that the outer parts of the plant that touch the covering will often receive minimal damage from frost bite. In order to prevent this from happening, a temporary support that will slightly elevate the covering above the plant must be utilized.

Freeze damage occurs whenever air temperatures drop below 32 degrees F. Whenever this happens, all parts of a plant are surrounded by the very cold air and a simple covering over the top of the plant is of little value.

However, if that covering is large enough to extend all the way down to the ground, it will trap some heat from the soil and may offer enough protection for the plant to survive with little damage if temperatures don’t go lower than 31 degrees F.

Should temperatures be expected to fall to 30 degrees and below, it is then necessary for coverings to extend to the ground and for a source of heat to be placed under the cover. Various coverings have been used, but they differ in their ability to retain heat so choose one that is the most likely to maintain temperatures above freezing.

Sources of heat like a 100 watt incandescent light bulb on the end of an extension cord are commonly used by many gardeners with generally pretty good success. The light bulb should not touch either the covering or the tree as a safety precaution.

It is imperative that coverings be opened or removed and the source of heat shut off as soon as the freeze danger has passed, especially when using tight covers made of clear plastic. This is because on a clear, sunny day temperatures under the cover can build up unbelievably fast and literally cook your plant.

Move large potted plants to wheeled dollies prior to low temperatures so they can be easily taken to safe environments until the freeze is over.


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