By Albert Mondor, horticulturist and biologist
Perennial cactuses that withstand our harsh winters? Yes, they exist! Of the four cactus species that grow in the wild in Canada, the brittle prickly-pear cactus (Opuntia fragilis) is assuredly the hardiest, contrary to what its name suggests. Indeed, it grows at 58º North latitude in Alberta, that is, less than 8º from the Arctic circle!
Scientists have determined that in its natural environment, Opuntia fragilis withstands temperatures around – 50 °C. Furthermore, they subjected the cactus to a temperature of −70 °C and immersed it in liquid nitrogen at −196 °C following slow freezing down to −40 °C. Well, after that extreme treatment, 50% of the stems survived! Unbelievable but true! For their part, the eastern prickly-pear cactus (O. humifusa) and escobaria (Escobaria vivipara), two other species of cactuses indigenous to Canada, survive at temperatures surrounding –35 °C.
Sold in some Canadian garden centres and nurseries, the cactuses described above can be grown outdoors in a flower bed, along with tropical perennials and annuals. With soil that drains well, such as the PRO-MIX® Cactus Mix, and a sunny location, those plants will grow easily without requiring any special care. Just let the sun and rain do their job!
Escobaria
(Escobaria vivipara) (Photo Credit: Stan Shebs)
Height: 5 cm
Width: 30 cm
Flowering: pink in July and August
Light: sun
Hardiness: zone 3b
Except its great resistance to cold temperatures, this spherical cactus is particularly beautiful at the beginning of summer with its large pink flowers.
Eastern prickly-pear cactus
(Opuntia humifusa)
Height: 20 cm
Width: 90 cm
Flowering: yellow in July and August
Light: sun
Hardiness: zone 3b
The eastern prickly-pear is a perfectly hardy cactus in our climate. In fact, if it’s covered with snow in the winter, this beautiful yellow-flowered plant quite easily withstands temperatures around – 35 °C. However, come spring, its stems are brown and shrivelled up. Generally, a few weeks are needed for the cactus to go back to its normal coloration and appearance.
Brittle prickly-pear cactus
(Opuntia fragilis) (Photo Credit: Dornenwolf)
Height: 10 cm
Width: 90 cm
Flowering: yellow in July and August
Light: sun
Hardiness: zone 1
The brittle prickly-pear is most certainly the most resistant to cold temperatures! It is quite unusual for an opuntia as it produces spherical stems rather than flattened stems like most of the other species. Over time, its stems form a thick carpet and bear pretty yellow flowers in the summer.
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