Growing Cactus in Cold Climates
It is almost an addiction once you have been bitten by the cactus bug. That being said, most of us collectors are stuck growing plants indoors as cold northern temperatures can kill our prized specimens. Interestingly, there are zone 4 cactus plants that can survive the temperatures in winter, which can exceed -30 degrees Fahrenheit (-34 C.) in some areas. The key is to choose cacti for zone 4 that are winter hardy and provide them with a microclimate that can shelter them somewhat. Deserts are generally hot, sandy, and dry. This is where we usually think of cacti growing. But even in such areas, the nighttime temperatures can cool down significantly, even reaching negative digits in the colder parts of the year. Many wild cacti must be adapted to the hot, dry summer days as well as the cold, often freezing winter nights. But there are things you can do to help too.
In-ground plants benefit from well-draining soil to prevent root damage when freezes do happen and root rot when soil becomes boggy. It may also help to install specimens in containers and move them when temperatures get to a threatening level. Additionally, you may also need to cover plants during periods of extreme cold to help keep the air around them slightly warmer and prevent ice or snow from damaging the stems, pads, and trunks.
Cold Hardy Cactus Plants
While most of the cold-hardy cacti are quite small, their unique forms can create a fun desert garden space even in the northernmost climates provided they get adequate sun exposure and good gritty soil. The Echinocereus group is one of the hardiest cactus plants. These types of cold-hardy cactus plants can withstand temperatures of -20 degrees Fahrenheit (-28 C.) and even colder if they are in a sheltered, southern area of the garden. Most of these are small mounded cacti, with numerous spines of various sizes and beautiful, almost tropical blooms. Claret cup cactus is one in particular. Similar to Echinocereus are the Mammillaria group of cactus. These ball-like cactus produce offsets and in mature forms can develop into rolling mounds of tiny cactus. Mammillaria also produce beautiful, vibrant flowers in spring to summer. Most of the plants in either genus rarely achieve more than 6 inches (15 cm.) in height. They are perfect for small rock gardens or at the edges of paths. Just be cautious where you put them due to the numerous tiny spines. Escobaria is another group of cold-tolerant cacti. Lee’s dwarf snowball looks just like its name indicates. It produces little puffed mounds with fine white hairs and over time develops into clusters. In addition to these, there are beehive cactus and plain’s pincushion. All are extremely tiny, rarely getting more than a few inches (5 to 10 cm.) tall but develop large, colorful flowers. Mountain spiny star is in the family Pediocactus and has terrific cold hardiness. These are ball cactus that rarely form colonies but may grow 12 inches (30.5 cm.) high and 6 inches (15 cm.) wide. They naturally occur in the mountains of the western United States. Compact, cute little cacti are useful for smaller spaces, but if you really want desert impact, the larger, pad forming cacti are your choice. The Opuntia family of cactus can grow 12 inches (30.5 cm.) high with pads of up to 5 inches (13 cm.) long. They can become spreading plants 4 feet (1 m.) wide with fleshy pads decorated with tiny spines in clusters. Many produce edible fruits, called tunas, and the pads are also edible once spines and skins are removed. Prickly pear is one of the better-known forms of Opuntia and form mats of pads several feet (1 to 1.5 m.) wide. It is a fast-growing cactus that is both drought tolerant and hardy in zone 4. Well-draining soil is crucial to these types of cold-hardy cactus plants. Avoid using organic mulches to protect the root zone as these can hold moisture. Cactus plants naturally reduce their water intake in cold weather and cells in pads dehydrate to avoid freezing and bursting in cold temperatures. Use stone chips or gravel as a mulch.
