December 28, 2008
Q: I am interested in growing a cactus as an indoor houseplant. Can you recommend some that would be good to start with and tell me how to care for them?
--Patrick O'Neal, Evanston
A: There are two types of cacti commonly grown as houseplants. The first is cacti that are native to rain forests. The other is cacti native to arid climates. Both types are easy to grow, but cactus from desert climates offer the classic cactus look and, if they are given enough sunlight, make low-maintenance plants that thrive on neglect. Two arid climate cacti that are good to start with are golden barrel cactus (Echinocactus grusonii) and hedgehog cactus (Echinocereus spp.). A golden barrel cactus has an upright barrel shape and golden spines and summertime flowers. A hedgehog cactus has small globe-shaped mounds that are covered with short spines and flowers. Other easy-to-grow options are the many types of star cactus (Astrophytum spp.), pincushion cactus (Mammillaria spp.) and prickly pear cactus (Opuntia spp.). Each of these cacti need several hours of bright sunlight. During winter this means a window facing south or west, and possibly supplemental artificial light. In summer, they can be slowly acclimated to growing outdoors in full sun. It's often proper watering that determines whether a cactus will grow successfully. Over-watering causes the majority of problems these drought-adapted plants face when grown indoors. To avoid problems, select cacti that are growing in porous containers and fast-draining soil, and never allow plants to sit in standing water. In the spring and summer, when cacti are actively growing, water well but then allow soil to dry out before watering again. Apply slow-release fertilizer once in the spring, or use water-soluble fertilizer monthly from June through September. In winter, when plants are dormant, cacti prefer cooler temperatures and only enough water to keep them from shriveling. Often this means applying a slight amount of water every few weeks. And while many houseplants need supplemental humidity to overcome dry winter air, cacti are happy and continue to thrive.