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  • Douglas Markoff

Native Ontario Cactus: You Can Grow That Here?

Updated: Mar 30

By Douglas Markoff

One plant that always attracts the passerby eye followed by a pointing finger is the Eastern Prickly Pear Cactus, Opuntia cespitosa.   A native perennial of Ontario, this Opuntia stands out since it is, after all, a cactus, and a cactus that grows contently in Ontario, at least up to zone 4 (I have been unsuccessful introducing plants in Ottawa).

Opuntia cespitosa ephemeral leaves. Photo: J. McRight
Eastern prickly pear (Opuntia cespitosa) ephemeral leaves. Photo: cool

Like all plants, O. cespitosa responds to the changing seasons.  As days shorten in fall, the photosynthetic oval Opuntia stems called pads (the botanical term is "cladodes") prepare for winter by slowly bending and laying flattish.  All through winter they lay dormant, tolerating salt spray and weighty snow and ice. 

As days become progressively longer and the sun’s angle warms the plants in early spring, they awaken and new vigorous stems with small ephemeral leaves emerge (see photo, left) that soon wither away, and flower buds begin to grow and orient almost vertically.  

A group of Eastern Prickly Pear cacti. Photo: Gail Krantzberg.

Heads up, taxonomy fans! On January 26, 2022, the common and scientific names of this species were updated on the Species at Risk in Ontario List from Eastern Prickly-pear Cactus (Opuntia humifusa) to Eastern Prickly-pear Cactus (Opuntia cespitosa) to be consistent with recent taxonomic changes. Photo: Gail Krantzberg.

Flowers emerge at the end of July through early August and their beauty is unsurpassed.  Flowers of the species we all know, O. cespitosa, feature 2” wide, funnel-shaped, bright canary yellow petals with an orange centre eye. Each flower is transient and remains open for one to two days.  Flowers are produced only on new pads (as observed) and like all true cactus, Opuntia flowers contain both male and female parts so they can self-pollinate. While various types of insects are attracted to the protein rich, sweet-smelling pollen, the native Ontario cactus flower structure accommodates pollination by bees, and when successful, the base of the flower swells, turns reddish and seeds form inside. 

Opuntia cespitosa flowers. Photo: Gail Krantzberg.

Opuntia flower anthers are thigmotropic: when disturbed by insects seeking out the pollen, they curl in on themselves to pollinate the stigma.  Photo: Gail Krantzberg.

Opuntias show variation in the density and length of their spines.  One cultivar has dark clusters of short, hair-like, barbed spines (called glochids) along all sides of the stem.  Opuntias have earned their name "Prickly Pear" cactus.  Take heed of their spines and be careful working around and handling this native.  Gloves help but do not guarantee immunity from the occasional spine in the finger, and the barbed glochids are the worst. 

Barbed glochids of the Eastern Prickly Pear cactus. Photo: Jeanne McRight.

I always use 12” long forceps (used in aquaria) to weed and remove leaves in the spring.  Removing leaves from around the plants is essential as excellent air circulation down to soil level is one key to growing them here and preventing rot.     

Other keys to successfully growing O. cespitosa lie in soil preparation, light exposure and duration and watering.  A highly porous, well-drained, gravely, airy soil mix is critical.   I use a mixture of 1/4”- 3/8”-1/2” granite, coarse sand, HPB (1/4” pieces of washed limestone), and some soilless mix. Some people add pumice to achieve the varying particle sizes one sees in nature.

Opuntias thrive in a baking hot south or west exposure, soaking up the sun all day or all afternoon.  Water your plants generously during their active growth period from May through September and especially during the heat of summer.  It is essential to allow the soil to dry out between waterings.    

All above-ground parts of Opuntias are edible.  In Mississauga, the fruit does not form into the large prickly pear fruit seen in the grocery, but may develop a slightly swollen, seed-filled, edible pulpy fruit.   The fruit and young stems may be cooked as vegetables (nopalitos in Mexico) after removal of all spines and stem ‘skin’.  In Mexico and other places in the world, some commercial production of Opuntia is devoted to cultivating cochineal scale insects harvested from the plants to yield a red dye, used as a colouring for foods, cosmetics and fabrics.

O. cespitosa forms colonies over the years, spreading horizontally as they creep along. Plants grow 1-2 pads per stem per season and can branch to form multiple stems.  We’ve seen a large patch in Stratford and during visits to South Africa and East Africa, found them naturalized and seriously invasive to people and wildlife. 

Opuntia cespitosa at Point Pelle National Park. Photo: Gail Krantzberg.

Photo: Gail Krantzberg.

We have observed large patches of Opuntia in southwestern Ontario at Point Pelee National Park.  Here,  O. cespitosa is considered a ‘species in recovery’ due to human trampling and habitat disturbance, forest succession and erosion due to high Lake Erie water levels.

  • Note: Recovery strategies and a Multi-Species Action Plan for Point Pelee National Park by Parks Canada has engaged Indigenous Partners through the First Nations Advisory Circle and participation in a site analysis workshop. Restoration activities were greatly reduced due to the restrictions associated with COVID-19; however, a new initiative was launched in fall 2021 with members of both Caldwell First Nation and Walpole Island First Nation (Parks Canada Agency. Implementation Report: Multi-species Action Plan for Point Pelee National Park, 2022). 

There are 300 species of Opuntia worldwide making it the most widely distributed genus of cacti, occurring from southern Canada to Argentina, and the most northern ranging and frost-tolerant of cacti, occurring as far north as northern B.C. and Alberta. There are six species of Opuntia on the Galápagos Islands, pollinated by birds, and are a major food source for giant tortoises, which remarkably tolerate the spines.  Finches are vital to the cactus, eating the fruit and distributing the seeds (Galapagos Conservation Trust, March 2017).

To propagate new O. cespitosa, take a clean, sharp secateur and cut the stem at its base where it joins another stem.  Stand the stem upright and allow the cut end to heal for 4-6 weeks in air (not in water nor in soil).  When fully calloused, pot the fully healed stem in your cactus mix, place in sunny spot but not baking, and water, allowing the soil to dry between waterings.

In Ontario, in addition to O. cespitosa there are other species with pure yellow flowers. O. fragilis features small oblong pads that snap off easily (an evolutionary adaptation to facilitate its distribution) and smaller flowers of yellow and orange eye.  There is a further species (or cultivar) with larger stems, longer spines and red flowers. 

Opuntia is truly a native perennial for our gardens, if you are so bold. 


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