Succulents are a diverse group of plants with varied tolerance for cool temperatures. Some succulents are tender plants that prefer warm climates, and others survive very cold temperatures. Although the term "succulents" refers to a wide group of plants, they share traits. All succulents have specialized tissue in their leaves and/or stems that allows their cells to store water. When these cells are full of water, succulents have a thick, fleshy appearance that sets them apart from other types of plants.
Even succulents that are hardy in U.S. Department of Agriculture plant hardiness zones with cold winters may be damaged by freezing temperatures. Freeze damage can occur when the temperature is between 32 and 24 degrees Fahrenheit. If the temperature stays at or below 20 degrees for an extended period of time, it will send hardy succulents not already dormant into dormancy and severely injure or kill tender succulents. Hardy succulents will grow back in spring, but tender succulents require frost protection to survive.
Even in USDA zone 10a, the temperature can drop below freezing, and plants that are hardy to only USDA zone 10 need protection when a frost is expected. These plants include the succulents blue chalk sticks (Senecio mandraliscae) and paddle plant (Kalanchoe thyrsiflora), both of which are hardy in USDA zones 10 through 11.
Plants that are hardy in cooler zones may also need frost protection. Aloe plants such as the spider aloe (Aloe humilis, USDA zones 9 through 11) can survive frost, but their flowers cannot. Frost will destroy the flowers unless the plants are covered or grown in containers and moved indoors.
More cold-hardy succulents, such as 'Autumn Joy' sedum (Sedum spectabile 'Autumn Joy,' USDA zones 4 through 9) and hens and chicks (Sempervivum tectorum, USDA zones 3 through 11), also called common houseleek, are rarely injured by freezing weather. 'Autumn Joy' can survive temperatures that dip to minus 30 degrees Fahrenheit and hens and chicks, to minus 40 F.
You can plan ahead to protect plants from frost when you're Don't plant frost-tender species in exposed parts of the landscape or in low spots, where cool air settles. Instead, plant on the south- or west-facing side of a building, fence, boulder or leafy shrub to provide natural protection for tender plants.
Another option is to plant succulents in containers, which can be moved to a sheltered location easily if the temperature drops. Succulents grow well in shallow pots filled with well-drained potting soil such as a commercially available cactus mix. You can also make your own succulent potting mix by combining standard potting soil with perlite, coarse sand and/or crushed volcanic rock so the finished mix is 2/3 to 1/2 potting soil.
Protection From Frost
When a frost is in the forecast, do not water succulents. They are more likely to survive freezing temperatures if the soil around them is dry. If you have time to plan ahead, keep the plants on the dry side well before the weather cools. If the succulents' specialized water-storage tissues in their leaves and stems are plump with water, their cells are more likely to burst when the temperature drops.
Move container-grown succulents to a sheltered location outdoors or take them inside your house. Use lightweight, breathable fabric to cover succulents that are planted in the ground. Remove the covers the next morning after the temperatures start to rise. Never use plastic to cover plants.
Care for Damaged Plants
If your succulents are damaged by frost, their affected leaves will probably turn white or a very light color soon afterward. Damaged leaves then turn black and mushy as they rot. If a whole plant was affected, nothing can be done to save it. If, though, only part of a plant was damaged, then the rest of it will often survive with a little help.
Remove rotting parts of every partially affected plant by using pruning shears to prevent the rot from spreading. Before and after pruning each plant and between pruning cuts, however, disinfect the shears by soaking them in a mixture of 1 part bleach to 3 parts water for five minutes; then rinse them with clean water. A plant cut in cold weather is susceptible to infection and further cold damage. So dust its cuts with sulfur powder to help prevent diseases. If a plant is not rotting, then wait until spring to remove its damaged leaves and stems.