University of Vermont
Department of Plant and Soil Science

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GROWING CACTI INDOORS

Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont

Want to exercise your green thumb this winter? Try growing cacti as houseplants. Desert cacti are well-suited to most indoor settings, where the relative humidity is rather low (20 to 30 percent) during the winter.
   
True cacti, a type of succulent, are native to the Americas. Many types may be grown as houseplants, each different in size, color, shape, and flowering habit. Among the most popular types are the star cactus, golden barrel, old man, bishop's cap, bunny ears, rat-tail, pincushion, Turk's cap, and ball cactus.
   
Most cacti purchased at plant shops, garden stores, florists, and grocery and discount stores prefer a growing space with plenty of sunlight.  Cacti grown on windowsills facing south usually flourish. The next best exposure is light from an east or west window, since it can provide direct sun for part of the day.  
   
Many gardeners think there is too little light in our area during the winter, but this is often not the case. With snow cover, more light is reflected during the winter than penetrates through shade trees around the home in summer.
   
If you just donít have enough light, you can supplement it with artificial lighting.  Be careful of the spot-type plant lights, as they may get too hot and burn the plants if closer than 6 inches or so.  Many use tube plant lights, or simply daylight or natural light fluorescent tubes, hung 6 inches or so over plant tops.  Use plant lighting, on timers, for 12 to 16 hours a day.
   
You can place the plants outdoors in summer, just donít move them from lower light indoors into direct full sun outdoors, and donít let them get watersoaked during rainy weather.
   
Perhaps the main trick to growing cacti is proper watering, and this varies with time of year or rather if the plant is actively growing. Many cacti have been killed from overwatering during the winter, including mine.  If the weather is cloudy, or even predicted to be cloudy, don't water. If in doubt whether the soil is dry, don't water.
   
When watering actively growing plants (usually spring and summer), water well, allowing excess water to drain.  If pots are in a saucer, empty the water out.  In the winter when plants generally take a rest, water very littleóperhaps once every couple weeks or even once a month.  Then, apply only a small amount to moisten the soil area around the roots.
   
Maintain the temperature during the growth period (usually spring and summer) at 60 degrees (F) at night and 10 to 15 degrees warmer during the day. During the dormant period (usually fall and winter), reduce the temperature to 45 to 55 degrees.  If most of your rooms are warmer than this, then place your cacti near a window (but not touching it) where the temperature may be five to 10 degrees cooler than in the middle of the room.
  
Fertilize the cacti several times during the growth period with a liquid fertilizer. Use a complete balanced fertilizer, or look for a fertilizer labelled for cacti and succulents.  For a general houseplant fertilizer, use only one-quarter of the label amount, every other watering.
   
When repotting, use a soil mix prepared and sold for cacti. Or make your own from one part coarse builder's sand, one part loam soil, and one part peat moss.  After repotting, donít water for a couple weeks to avoid any rots on roots damaged during repotting.
  
Finally, if you brush against your cactus and get a few spines stuck in your fingers, use heavy duty tape (sticky side to the spines) to pull them out.
 

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