by Don Janssen, Extension Educator
If you think about where cacti live in the wild, it's not surprising that they don't flower readily in the home. Low light, warm temperatures in the winter and too much water are typical features that make most homes a hostile environment for desert plants. Turn those conditions around -- provide bright light, cool temperatures and little to no water -- and you may get cacti to flower.
Obtain cacti from a knowledgeable individual who can help you pick species that won't keep you waiting for flowers for 50 to 100 years. Families of cacti that bloom reliably indoors include the Mamillaria, Gymnocalycium, Parodia and Notocactus.
When plants need repotting, use a mixture of equal parts bird gravel or other aggregate, potting soil or sterilized garden loam, and leaf mold. Water thoroughly only when the top inch of this medium is dry. The surest way to kill cacti is to overwater them. A sunny south, southeast or east window is ideal. Cacti can go outside during the summer, with some protection from direct sun.
Following these guidelines should keep your cacti healthy and growing well, but it won't necessarily make them flower. To do this, you need to nudge them into a dormant period with a combination of cool temperatures -- a night maximum of 40 to 50 degrees F -- and four to five hours of bright light daily. A cool, dry greenhouse, if you have it, is one way to provide these conditions, but a covered basement window well, a glass-enclosed porch, a window-mounted mini-greenhouse, an unheated upstairs bedroom or an attached but unheated garage can fill in. If you don't have a sunny, cool spot, add light or close a heat register or otherwise alter the environment to provide the right combination of conditions.
Though cacti need chilly temperatures in the winter, most of them won't tolerate frost, so make sure the temperature in the space you've chosen stays above freezing.
For many houseplant gardeners, the hardest part about overwintering cacti is watering -- or rather, not watering. Give them no water during the cold dormant period -- from mid- to late November until March. Place the plants in that cool, brightly lighted spot and ignore them.
If the plants aren't too young, they should flower in spring. Resume watering when the flowers start to show. Then begin tapering off again in late August to ease them into their next dormant period.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office