Cacti (Cactaceae, USDA plant hardiness zones vary widely by type) are iconic to the hot, dry desert landscape. However, cactus can be found in the natural landscape as far north as Canada and as far south as Argentina. Additionally, there are winters when even the most southern states in the United States face frost and snow. So, if you are caring for a cactus plant, what can you do if your cactus froze during a cold snap?
Cactus Plant Basics
Cacti are succulent plants. This means that they can store water in their leaves (think of an agave) or in their trunks (a barrel cactus). Cacti do need to be watered, and they need nutritious soil in order to thrive.
These plants can live in deserts, grasslands and forested areas. One of the most common grassland cacti is prickly pear (Opuntia, USDA zones 4 through 10). Varieties of this plant also thrive in the desert. A tropical cactus would be the Thanksgiving or Christmas cactus (Schlumbergera), USDA zones 9 to 11). Among the most famous desert cacti is the mighty saguaro (Carnegiea gigantea, zones 8a to 11b).
Cold Weather Cactus
It is important to understand the heat and water needs of your cactus plant. Tracing your plant's background to learn if it is a cold weather cactus can help you anticipate the needs of your plant.
Some cacti are hardy in zone 4, while others live best in Zone 7 or 8. After you have verified your cactus's name, determine in which zones it lives best, and then check the USDA Plant Hardiness Zone Map, cross checking your home zone with the plant's hardiness zone.
Saving a Cactus's Life
Some cacti can live for over 100 years. This means that they are generally a hardy plant that can take some abuse from the weather. A cactus should not wither after getting a little cold or a touch of snow, especially if the chill is short.
Gardeners should not water a succulent right before a frost, as dry soil is best for these plants during cold weather. It also helps to have a cactus on high ground, rather than at the bottom of a hill, where chilly air can collect and surround a low-lying cactus.
Before it freezes, cover the cactus with burlap cloth, a blanket, a sheet or a frost blanket. Cover the plant while the sun is still up, and remove it in the morning after the frost has left and it is warmer outside. If it will be cold for several days, you can leave the covering on for a week (or more) without harming the plant. Columnar cacti, like organ pipe cactus, are most vulnerable at the tips of their areolas (branches), so you can cover these with a frost blanket or with Styrofoam cups.
Treating Cactus Frost Damage
If a cactus has suffered frostbite, the plant's flesh may first turn white. Cactus frost damage will then become soft, wilt and turn black. Some cacti can slough off these frozen patches on their own.
However, you may wish to prune off the dead parts of the plant, especially if you think they are becoming infected. If at all possible, wait until all danger of frost has passed before pruning the cactus. If you must prune it sooner, dust the cut with sulfur powder to prevent further infection, as the cold makes open cuts on a cactus susceptible to pathogens.
Trim a cactus at its joints, not in the middle of its pads or at the center of a column.