Cacti are some our most spectacular native flowering plants, but often our most overlooked wildflowers when planning and planting a xeriscape. Cacti not only contribute stunning flowers in spring and summer, but also provide year-round interest with their structural evergreen stems and geometrically arranged spines.
Native only to the Americas, cacti represent a diverse group of perennials that have adapted to a wide range of habitats. There are a number of species that grow in USDA zone 7 and colder areas. These cold-hardy beauties can be successfully mixed into landscape plantings when their cultural needs are understood and provided for.
The keys to successful cultivation of cacti include:
proper soil preparation,
correct placement in the landscape
planting them with suitable companion plants
Cacti require a fast draining soil. This means no clay and no added compost, peat moss or other soil conditioners which make the soil too rich in nitrogen and humus. I recommend only Planters II Natural Trace Mineral Fertilizer and Yum Yum Mix. I also recommend a berm created with a mix of small gravel, coarse sand, and very little soil.
Most cacti prefer full sun and benefit from warm protected microclimates where rocks, buildings or pavement absorb and hold heat.
Cacti benefit when grown with other plants as long as they’re not smothered by large and fast growing companions. In wetter climates companion plants also help pull moisture from the soil and keep cacti drier. Clump grasses are particularly helpful in this way.
In the wild cacti are rarely if ever found growing only with other cacti. Unfortunately many cacti are relegated to cactus-only plantings. This “pincushion” look deprives the gardener of the opportunity to combine them in artful ways with non-cacti plant and thus extend the blooming season.
A number of cacti are native to the Great Plains. Whether found growing directly in the grasslands or in rock outcroppings, these species are the most moisture tolerant, cold hardiest and easily grown of the barrel-type varieties and include:
Echinocereus reichenbachii and reichenbachii subspecies albispinus, caespitosus and baileyi
Other ornamental species are native to high, dry cold areas of the southwestern United States and northern Mexico. They aren’t quite as cold-hardy and are bothered by extreme temperature swings in the spring and fall. They also like hotter, drier conditions, especially during the winter months. This group includes: Echinocereus fendleri, Escobaria orcuttii v. koenigi, and Ferocactus wislizenii.
For companion perennials with these, try the following:
My favorite species from the intermountain West can be planted with either of the above groups. Echinocereus triglochidiatus (Claret Cup) with its late spring display of orange flowers is our largest and showiest cold-hardy clumper. White Sands is the biggest and most vigorous growing member of the species and matures to a massive (2-3’ tall x 18-24” wide) cluster of 5” diameter stems. It can be used as the centerpiece for any xeric planting. I like to combine it with Sotol (Dasylirion wheeleri), the rare Yellow Texas Yucca (Hesperaloe parviflora “Yellow”), and Beargrass (Nolina microcarpa).
Maintenance is the final component to a healthy cactus planting. Always keep cacti mulched with gravel. I prefer crushed (angular) gravel to a depth of 2”. Remember to replenish gravel mulch annually; freezing winter weather causes the soil to contract and expand pulling the gravel down into the soil and thinning the layer above ground.
Established plants grow fastest when watered regularly, once every 7 to 10 days during the heat of the summer (when there is no rain). Stop watering by early September to let the plants dry down and shrivel in preparation for winter. Fertilize no more than once a year. I like to top-dress with Yum Yum Mix at the start of summer.
Trim companion plants during the growing season as needed if they overgrow their cactus neighbors. Remove all fallen leaves from around the cacti, and cut back any plants that create winter shade. In wetter climates that get a lot of winter/early spring rain, it is helpful to create an open-ended tunnel with plastic sheeting and bamboo hoops to keep the bed dry. Remove in mid-spring as the plants begin to wake up and grow. Summer is an ideal time to transplant heat-loving cacti and desert plants and grasses.
For more information, refer to these books about cacti:
Agave havardiana (Havard's Century Plant) grows to an imposing size (30" tall x 36" wide) at maturity! Native to the Glass Mountains of west Texas, this succulent has proven itself to be very cold-hardy. Drought resistant/drought tolerant plant (xeric).
18" tall x 18-30" wide. High Country's form of Agave parryi comes from the high cold desert near Flagstaff, Arizona. It is exceptionally cold hardy with thick silver-gray leaves that grow to form a large sized rosette when mature.
Drought resistant/drought tolerant plant (xeric).
15-24" x 18-24" wide. Echinocereus triglochidiatus ('White Sands' Claret Cup Cactus) is without a doubt the fastest, largest and most spectacular of any claret cup cactus. The robust, stoutly-spined stems are topped with glowing scarlet flowers in late spring and can grow to a height of 3 feet under favorable conditions. Drought resistant/drought tolerant plant (xeric).
Scarlet Hedgehog Cactus or Needle-Spined Claret Cup (Echinocereus coccineus) is an outstanding species that blooms in mid-spring with a profusion of hummingbird-attracting scarlet-red flowers held over a mound of tight clustering stems.