With the arrival of fall, cold temperatures are just around the corner, so it’s time to make sure that you know how to protect your plants from frost damage.
But, before we talk about how to protect plants from the cold, let’s talk about how the freezing temperatures affect them.
Causes: Cold damage occurs when temperatures dip below the minimum that a particular type of plant can handle. In many areas of the Southwest, when we talk about cold, or frost damage, we are typically referring to plants that are considered to be “frost-tender.” These are plants that are native to tropical or semi-tropical climates, where freezing temperatures are non-existent or rare. Examples of frost-tender plants include bougainvillea, citrus, lantana, and tacoma species such as yellow bells (Tecoma stans stans).
Freezing temperatures occur when the thermometer goes down to 32 degrees Fahrenheit, or lower, and causes damage to a plant’s leaves, stems, and branches.
The farther below 32 degrees that temperatures dip, the more severe the damage that occurs in plants. The reason for this is that cold temperatures cause ice crystals to form within the plant’s cells, which pierce the cell walls, causing the contents leak out. This causes the leaves to turn brown and crispy. At first, the damage isn’t too evident, but the effects continue to progress as long as the freezing temperatures do. Frost damage occurs first on the outer part of the plant and gradually moves inward with additional instances of freezing weather. So, if you experience a relatively mild winter, with only a few nights in the low 30’s, the damage to frost-tender plants may be minimal. If temperatures then dip into the 20’s, the damage will be more severe, as more ice crystals will form within the plant.
Frost Protection: There are two ways to deal with freezing temperatures. The first is to do nothing and simply prune away the frost-damaged growth in spring, once the threat of cold weather has passed.
The second option is to cover plants with frost cloth, old blankets, sheets or towels during the night when temperatures fall below 32 degrees. As heat from the ground radiates upward, the covering helps to trap that heat and increases the temperature around the plant by a few degrees, which can prevent or lessen frost damage. The entire plant needs to be covered with no gaps between the covering and the ground or warm air will escape.
During the day, uncover the plants to allow them to get sunlight, which also warms the soil around the plants.
Sometimes, you will see plants partially covered and this does little to offer any protection to plants as the heat from the soil isn’t contained around the plant.
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If you don’t have a closet full of old blankets or towels, you can opt to use “frost cloth,” which is a semi-permeable covering that holds the heat in, but allows the sunlight to reach the plant and warm the soil too. The great part about using frost cloth is that it is reusable and you don’t have to uncover plants during the day.
For larger shrubs or small trees such as citrus, you can use a large blanket, or a “plant jacket,” which is made out of frost-cloth material, and is a good option for big plants.
It’s not unusual for your local nursery or garden center to run out of frost cloth when the forecasters are beginning to predict the first freezing temperatures, so if you don’t have a closet full of old blankets and towels, you might want to stock up ahead of time or your plants may end up looking like those above.
Now that you know how to protect your plants from frost damage, don’t throw away those old bed sheets, towels, and blankets. Save them instead for your frost-tender plants on chilly nights.