Why Not Cover Plants with Plastic for a Frost?

Answer

Unanticipated frosts can force gardeners to scramble for anything to use as protection for their plants that are not quite dormant or have just begun to awaken. Cotton was the material of choice for Grandma’s bedsheets and comforters, but in today’s environment, it would appear that a more contemporary material, such as plastic, would provide substantially greater protection for plants. Plastic is a useful material in some circumstances, but in the vast majority of cases, the traditional approaches are preferable. {{!! -!! Frost may cause harm to plants even if the temperature does not reach freezing; it only has to become cold enough for water vapour to condense on plant tissues that have been chilled to a temperature that is just below freezing for this to occur. This is precisely what takes place whenever there is a radiation frost, which is the most frequent kind of frost occurrence. Heat escapes from vegetation, buildings, and even the earth itself when there is a radiation frost because the atmosphere is so quiet. {{!! -!! During a radiation frost, the rate of heat loss from plant leaves is far higher than that of the items in the surrounding area, the ground, and even the air itself. Because of the temperature differential between the air and the leaves, ice crystals may develop and grow through the surface cells and thin tissues of the leaves. When the temperature of the tissues rises beyond freezing, the frost on them melts, and this causes their contents to seep out, which ultimately results in the death of the punctured cells. Some plants are able to recover from this kind of damage without any problems; although they may appear to be in worse shape than before, their growth will proceed as usual. Some plants, particularly those that are native to tropical regions, are unable to withstand even the occasional frost and may perish completely if exposed to it. {{!! -!! Plastic may seem like a nice idea for protecting plants from frost, but it is just not thick enough to provide any kind of insulation to the plants. Because frost occurs when leaf temperatures drop, merely covering the plant won’t be enough to protect it; the secret is to use an insulated covering to trap heat that’s emanating from the ground. Covering the plant with a blanket won’t work. Plastic that comes into contact with plants is, in many instances, even worse than providing no protection at all because it can trap moisture against plant tissues, which can result in more severe freeze damage. On the other hand, plastic may be an efficient weapon in the fight against frost if it is used in the form of a row cover or when it is put directly on the ground around a plant. {{!! -!! In general, you should remove any plastic coverings from your emergency plant supply closet; however, heavy drapes, thick bedspreads, and cardboard boxes are still good options. Just make sure that the covering you use on your plant extends all the way to the ground so that it can effectively trap warm air under the plant’s canopy. Your plant will be protected from frost to an increasing degree depending on how well the cover does this. Gardeners typically construct tall posts or forms around their frost-sensitive plants in regions where frost is common and unexpected. This allows them to drape their covers over the plants and secure them without having to worry about the covers bunching up or blowing away during the night.

Frost

It doesn’t have to freeze for plants to be damaged by frost; it just has to get cold enough for water vapor to condense on plant tissues that have been chilled to just below freezing. This is exactly what happens during a radiation frost, the most common type of frost event. During a radiation frost, heat from plants, buildings and even the ground are lost to the still atmosphere.

Plant Tissues

Plant leaves lose heat much more quickly than surrounding objects, the ground and even the air during a radiation frost. This difference in temperature between the air and leaves encourages the formation of ice crystals that grow through surface cells and thin tissues. When tissues warm above freezing, melting the frost, their contents leak out, causing the death of these punctured cells. For some plants, this kind of damage is no problem — they may look a little worse for wear, but will continue to grow normally. Other plants, especially those originating in tropical areas, can’t tolerate even the rare frost and may be killed to the ground.

Plastic for Frost

Plastic seems like a good idea for frost protection, but it’s just too thin to provide any insulation to plants. Since frost forms when leaf temperatures dip, simply covering the plant isn’t going to be enough to protect it — the trick is to use an insulated covering to capture heat that’s radiating from the ground. Plastic that touches plants is even worse than no protection in many cases, since it can hold moisture against plant tissues and cause more serious freeze damage. However, when used as a row cover or placed directly on the ground around a plant, plastic can be an effective tool in the battle against frost.

Better Coverings

In general, you should toss plastic covers out of your emergency plant supply closet, but thick bedspreads, cardboard boxes and heavy curtains are still winners. Just ensure that when you cover your plant, the cover reaches the ground, trapping warm air under the plant’s canopy. The better the cover does this, the safer your plant will be from frost. In areas where frost is frequent and unpredictable, gardeners often erect tall stakes or forms around their frost-sensitive plants so they can drape their covers over the plants and secure them without worrying about the coverings bunching or blowing away in the night.