Cactus Damage at Freezing Temperatures

Symptoms

• Each of the many species of cactus varies in its susceptibility to winter injury. Nearly all cacti, however, are intolerant of temperatures below freezing. If your cacti have been subjected to below-freezing temperatures, the earliest symptoms will show on new growth tips. The exact appearance of the symptoms of winter injury vary from species to species, so if you see strange growth symptoms immediately following cold weather and that cannot be associated with any other possible ailments, the cause may be winter injury. To confirm the diagnosis, send a tissue sample to a university extension office and have it diagnose possible winter injury.

Other Problems

• The biggest problem with frost-damaged cactus is not the damage itself but that the damage can leave the cactus susceptible to other, more serious ailments. Bacterial and fungal rot diseases develop from various kinds of damage including insect and frost damage. Bacterial soft rot, for example, causes spots of necrotic tissue that appear soft and dark. Control measures usually involve pruning off the diseased tissue with sterilized pruning equipment to prevent the rot from spreading to the other parts of the cactus. Rot diseases can threaten the long-term health of a cactus if they are not properly managed, so protecting your cacti from winter damage is an important part of cactus cultivation.

Preventing Frost Damage

• The best winter injury control measures are those that are preventive in nature. If you live in an area that sees freezing temperatures many times throughout the year, you may be spending more time treating winter injury than enjoying healthy cactus plants, so you may want to consider forgoing cactus for other plants. If you live in an area that is conducive to cactus growth, however, look for the most cold-tolerant varieties of cactus available for purchase and cultivate those in lieu of less cold-tolerant varieties. Avoid excessive fertilization and irrigation early in the growing season as these leave cacti more vulnerable to frost damage.

Protecting Cacti From Cold

• Of course, if you are facing a hard freeze in the middle of the winter, you will need to take steps to protect the cacti from damage. Just before the freeze, cover the cacti with a frost blanket, sheet or other similar material; never water the cactus just before the freeze. During the daytime when temperatures have raised above freezing, the protective layers should be removed to ensure that the cacti can receive enough sunlight.