By Bruce de Cameron, Colorado State University Cooperative Extension Master Gardener, Denver County
Winter hardy cacti are a natural choice for water-wise Colorado gardens.
Perfectly suited to hot, dry summers and moderate winters, these cacti can be hardy to -40 degrees Fahrenheit and grow in brutally hot exposures that few plants can withstand. Their unique beauty, colorful blooms and low maintenance requirements make them deserving of a first and even second look.
Cacti thrive with maximum sunlight and full exposure to drying winds. Choose a south, west or southwest exposure. To survive western winters, all cacti need loose soil and excellent drainage. Unlike other garden plants, the challenge in growing cacti is the elimination of excess moisture.
Both sun exposure and drainage requirements can be met by using ample gravel or sand on a sunny hill or raised bed. Five inches of sand with a small amount of organic matter mixed in is ideal. A thin mulch of stone chips or gravel will reduce the chances of crown rot.
Cacti naturally reduce their moisture content and shrivel with the onset of winter. Dehydration prevents cactus cells from bursting when they freeze. Excess moisture during autumn months can cause cacti to hold too much water and suffer freeze damage.
Most cacti also change color in winter. This natural occurrence has nothing to do with the plants being sick. As plants become less active and the amount of green chlorophyll decreases, the red, orange and other color pigments show through the pads or stems.
Don't mulch cacti for winter protection. Mulches retain too much moisture. The only safe ground-level cover is snow. An above ground cover that protects cacti from excess moisture may be helpful for the more difficult ball-type varieties.
Types of cacti that are winter hardy include Opuntia (prickly pear), Coryphantha, Echinocereus, Pediocactus and Neobesseya. Of particular interest are some of the following recommended Opuntia species: Opuntia compressa - fast growing with numerous yellow flowers and few spines; Opuntia humifusa - large yellow flowers and edible fruit; Opuntia polycantha - yellow flowers and numerous spine; Opuntia fragilis - a smaller sized plant with large yellow flowers; Opuntia rodantha - spiny with pink flowers.
Hardy ball-type cacti that may need protection from excess moisture and humidity include: Coryphantha vivipara - pink or yellow flowers; Echinocereus viridiflorus - yellow flowers;Echinocereus triglochidiatus - red flowers; Neobesseya missouriensis - yellow flowers; Pediocactus simpsoni - pink flowers.
Why not give winter hardy cacti a try in that hot, dry garden spot where no other plant succeeds? They do lend a particularly southwestern feel to the garden.
For more information, consult the Colorado Cactus and Succulent Society or your favorite nursery or garden center. You also can call the Colorado State University Cooperative Extension office in your county.
Photos: Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010