Gardening

Getting Your Globular Cactus to Bloom

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Mammillaria zeilmanniana is an easy globular cactus to bloom. Source: Dornenwolf, Wikimedia Commons

The easiest desert cacti* to get to flower in the home are the small globular ones (Gymnocalyicum, Rebutia, Echinopsis, Mammillaria, etc.). Prickly pear cacti (Opuntia), with their flat pads, and large columnar or barrel cacti are either difficult to get to flower or take decades before they are mature enough to bloom, but many globular cacti are mature and ready to flower when they are less than 2 years old.

A Summer and Fall Outdoors 

To get a globular cactus to bloom, start by putting it outside for the summer, after proper acclimatization, of course. That’s because sunlight indoors passes through a glass window and glass filters out the ultraviolet rays. Ultraviolet light is not needed by most plants and is in fact even harmful to many, but desert cacti actually grow best when they receive ultraviolet rays. So a summer outdoors really does them a great deal of good.

Video by Greg Krehel showing Echinopsis flowers opening in slow motion: just beautiful!

Water and fertilize your cactus regularly throughout the summer, like any other container plant, as this is its growing season. However, when autumn begins, it’s time to place the plant in a spot protected from rain, perhaps under the overhang of the roof or behind a window frame leaning against a wall. That’s because a period of drought is one factor that stimulates bloom in many small cacti. You can, of course, water when the soil is thoroughly dry, but otherwise, it’s best keep the rain off it throughout the fall. Keep your cactus outside as long as possible in the fall and don’t bring it back indoors until there is a real threat of frost, as cool or even cold nights are the second factor that stimulates cacti to bloom.

When the plant has had a few months of cold nights and drought, bring it indoors and place it in front of a window, preferably in a cool spot (although by now, many small cacti will have had their required cold treatment and wouldn’t be too bothered by a bit of warmth). Through the winter, continue watering only when the soil is really dry.

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Rebutias, like this Rebutia heliosa, are easy to bloom and very colourful.  Source: Jonathan Cardy, Wikimedia Commons

Flowering should occur somewhere between mid-winter and late spring, depending on the species and the growing conditions. If it still hasn’t bloomed by spring, put it outdoors again for the summer … where it will likely bloom in short order.


*Epiphytic cacti or jungle cacti, like Rhipsalis and Christmas cacti (Schlumbergera) are also easy to get to bloom … but aren’t desert cacti and shouldn’t be treated as such.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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