Do I Need to Cover My Cactus at 25 Degrees Fahrenheit?

Cacti and Cold Temperatures

• Cacti contain a high percentage of water to sustain them through long periods of drought. Their ability to store water is the most important means of survival during the hot season, but this same ability also can kill a plant in below-freezing temperatures. At 25 degrees Fahrenheit, the water within cactus can freeze. The water freezes as it expands and can rupture the membranes. Plants that are native to freezing temperatures have adapted by preventing the water from freezing, usually by storing salt. Although some cacti grow naturally in freezing temperatures, such as Sempervivum and Oreocereus, the vast majority of cacti do not. It is for this reason that the vast majority of cactus species should be protected from 25 degree temperatures.

Sheltering the Plant

• Cacti can be protected for short periods of sub-freezing temperatures, but even covered plants will not survive a long winter. Cactus may be covered with bags, newspaper or plastic. Smaller plants, however, may not survive even if covered because frost damage is substantially more severe at ground level. Smaller plants should be moved indoors until they are larger. Planting cactus close together also can be effective at guarding against frost damage, particularly if groups of plants are covered together. Positioning plants under a tree or the eves of the house can provide some protection against freezing temperatures.

Potted Plants

• Potted plants are the easiest to protect from frost damage because they can be moved. The pots can be buried to keep a natural look and moved indoors in periods of freezing temperature. This is a popular method of cacti and succulent enthusiasts in northern Europe. The disadvantage to keeping cactus in pots is that they do not grow as quickly as those in the ground. Each cactus enthusiast must balance the convenience of potted plants against their slower growth rate. Of course, the plants could be dug out of the ground and moved to pots before the winter season arrives.

Treating Frost-Bitten Plants

• Frost damage is most likely to first appear on smaller portions of the plant, particularly around the base. The leaf tips of some species are also highly susceptible to damage. If you suspect that the cold temperature is starting to have a negative effect on the plant, steps should be taken immediately to protect the plant from further damage. At a minimum, the plant should be covered. If possible, move the plant indoors. Most cacti are summer-growers, meaning that they go dormant in the winter time. For this reason, avoid the temptation of removing damaged portions of the plant until summer.