Cacti in your garden? Not likely, you might say. Aren't they spiny succulents that grow in deserts? Surprisingly, the cactus family has several rock-hardy members that can survive practically anywhere in Canada.
Unique to the Americas (save for one tropical species, Rhipsalis baccifera, which has somehow spread to Africa, Madagascar and Sri Lanka), cacti are wide-ranging, from Patagonia to northern British Columbia. They're prized for their thick, succulent, generally prickly stems that contrast beautifully with most leafy plants. The stems are evergreen, ensuring year-round interest, and the spines are often strikingly colourful. Plus, they produce brilliantly coloured flowers in June or July; some even bear attractive fruit.
Although we often think of cacti as being frost-tender, many are thoroughly adapted to cold winters. Indeed, four species are native to Canada, and many hardy ones are found in alpine areas throughout the Americas. To help them survive frigid temperatures, hardy cacti expel water as nights become chillier, even when it rains. This is a clever trick: water expands when it freezes, so water-filled cells would rupture in winter, but drier cells can survive unharmed.
Keys to cultivating
Here's what's needed for successful growth:
• a species adapted to your climate; cacti sold as houseplants are unlikely to be hardy
• full sun to very light shade
• perfect drainage-sandy or gravelly soils or a slope is ideal; poor drainage may cause rot
• any soil type, from alkaline to moderately acidic
• light fertilizing; too much nitrogen can cause a spurt of growth that won't harden off before frost arrives. Use a slow-release, low-nitrogen, organic fertilizer such as 3-5-3
• in areas of heavy snow, protect plants from being crushed with a simple structure of planks resting on cinder blocks
• native cacti are susceptible to cactus borer; to control, cut off any infected pads