Cold-Hardy Cactus and Succulent Gardening
Do you know there are cacti and succulents that can live outdoors all year long in your garden? We call these plants cold hardy. Cold hardy is relative to where you live. Here in the St. Louis metropolitan area, the plant hardiness zone is 6b (-5 to 0) or 6a (-10 to -5b), depending on the county you live in.
By Jolie Krupnik & Chris Walker
[This article was first published in The Gateway Gardener June 2018 issue.]
Do you know there are cacti and succulents that can live outdoors all year long in your garden? We call these plants cold hardy. Cold hardy is relative to where you live. Here in the St. Louis metropolitan area, the plant hardiness zone is 6b (-5 to 0) or 6a (-10 to -5b), depending on the county you live in. This means that the plant must be able to survive the lowest of the temperatures in your plant hardiness zone.
Are you space-challenged in the house or greenhouse? After months of what is considered to be drought conditions in our area, do you want to xeriscape, that is, create an environment that uses little or no irrigation? Cacti and succulents are drought tolerant, low-maintenance plants and can be interesting, sculptural additions to your garden.
A cold hardy garden doesn’t come without its challenges, though—where and when to plant, your soil mix and the weather are all factors in creating and maintaining a successful cold hardy garden.
Many cold hardy plants are readily available for purchase in our area. The genus Echinocereus has some of the most successful winter-surviving species. You will see great success with E. viridiflorus, E. reichenbachii and E. triglochidiatus. E. viridiflorus offsets barrel-type clusters and its yellow-green flowers are smaller than the other species. E. reichenbachii has large, stunning pink flowers, clustering stems and seems not to mind our humidity and rainfall. E. triglochidiatus also has clustering stems but deep, red flowers. While mostly spined, there is a form of this species that is spineless known as “inermis” that adds a nice contrast.
There are over a dozen hardy species of Opuntias, and many new hybrids are being introduced with dazzling flower blooms in an array of colors. You may see your opuntias shrivel up and withered in the winter, but this is natural. In the spring, the pads will plump up, and should bloom. O. humifusa, O. polycantha ‘Peter Pan’ and O. fragilis (debreczyi) v. denuda (Potato Cactus) are some of the more commonly known and reliable opuntias. When handling opuntias, beware of the glochids, which are small, prickly hairs that pierce the skin and are difficult to pull out. Opuntias can overtake your garden, but snipping off pads at the joints will keep them contained.
A popular cold hardy succulent is Hesperaloe parviflora, whose red tubular flowers grow on a long 2-3 foot stalk. Its leaves are long and cylindrical with tiny hairlike filaments along the edge. Yucca nana is one of the smallest yuccas but showy in its architectural form; perfect for the corner of your garden.
Various sedum and sempervivum make great accent plants that show off cacti. Other non-succulent plants such as creeping thyme or savory make great accents.
You want to plant in the spring after the last frost, around mid-to-late April. This will give the roots time to establish themselves and a better chance of surviving our harsh winters. Most cacti need at least six hours of sun exposure in order to bloom. Before planting, be sure to acclimate your plants to the sun.
A sloping area or berm with southern exposure is the ideal location for a cold hardy garden. A slope allows the rain to run off. If the water sits, your plants will develop root rot and die. Your soil mix needs to be well draining. St. Louis soil is clay-based, which is not well draining. You can amend the clay soil with topsoil and aggregates like pea gravel, pumice, river rock, trap rock. Some gardeners will dig out 6-12 inches of the existing soil and fill in with aggregates. Others will amend the existing soil with aggregates for each individual plant, which could cause small “ponds” because the water can’t escape beyond the clay surrounding your amended area. Planting on berms (raised areas) or in between the tops of two rocks can provide a well-draining environment.
Adding rocks to the garden can be functional as well as decorative. Rocks can provide shade during the hot summer afternoons, divert water away from the plant, block winds and provide warmth in the winter, which the plants will appreciate. Rocks, as well as drift wood or other objects also add an aesthetic element; their placement can move the viewer’s eyes from plant to object to plant around the garden.
Once established in the garden, a cold hardy garden requires infrequent watering and great visual pleasure.
Jolie and Chris are avid cacti and succulent enthusiasts, and both have maintained cold-hardy gardens in the West County St. Louis, MO, area for several years. Jolie is the Digest Editor and Chris is the Program Director for the Henry Shaw Cactus & Succulent Society. Guests are welcome to attend an HSCSS meeting. Go to HSCactus.org for more information.