Throughout my gardening life there have been many plants that I tried to grow with middling success, until I observed them growing in the wild. Sarracenia (pitcher plants), venus fly trap (Dioneae muscipula), episcia, and ginger are just a few that come to mind. Seeing them in their natural habitat helped me understand something about the soil, light, moisture, or the communities they grow in that allowed me to better approximate their needs at home in my own garden and pots.
In June 2011 I travelled to Denver, Colorado to speak at the Denver Botanic Gardens. One of many things I was excited to see in the area were cold hardy cactus growing in the wild. I’ve been growing Opuntia humifusa and other hardy cacti in pots for years and had only recently began to have success with them in the ground. But I still felt that there was something that I was missing.
Until that time I had only seen hardy cacti growing in gardens. Gardens are environments planted, maintained, and controlled by humans. To varying degrees, we gardeners are selective about what we plant, how we plant them, and how we allow them to grow (or not grow). This is cultivation. Even those of us that espouse a “wilder” temperament and style tend to do at least a little pruning and weeding. As a result, the communities that are formed in a garden are often very different than the ones that are formed when plants are left alone.
I spotted the first hardy opuntia off of a hiking trail on a hill in Boulder, Colorado. [Thanks to Shayna for taking us on a field trip there!] I knew I would find them there and I knew they would be small so I started looking down low the second my feet hit the trail. What I did not expect was the field of thick grass, nor did I expect to find the opuntia blanketed and completely shaded out within it!
This confusing predicament followed me throughout the trip. Wherever I saw hardy opuntia, whether it was on that hill in Boulder, or later, on the sides of dusty dirt roads or the edges of farmland in Nebraska and the rolling hills outside of Denver — they were always almost entirely covered by grass!!
I’ve thought a lot about this since the trip. I’ve searched for an explanation in books. I’ve asked other hardy cactus gardeners. I keep coming up short. Clearly the opuntia do not mind being shaded out by the grasses. They were robust plants. The competition for other resources (like water) didn’t seem to hurt their numbers. The only explanation I can muster is that as the opuntia do their thing and spread through the grassland, the grass provides coverage from extreme wind and sun. The elevation is much higher there than it is here in Toronto. The sunlight is more intense and they receive more days of it. My guess is that the web-like roots of the grasses also helps to keep the cacti in place, especially when it is windy. They also help prevent erosion, so while there may be competition for resources, the grasses also help to prevent those resources from escaping faster.
This summer I did a little test in my dry bed garden. The ‘Buttercream’ California poppies that I planted came up fast and furiously and many grew over the opuntia. And I let them do it. I cut them back here and there to let light in. After-all, we are not as high elevation here and I know that the sun is important in helping them survive the winter. However, I allowed them to grow more freely than I would have had I not visited Colorado and Nebraska and saw the opuntia growing like this. It wasn’t just the conditions itself that I was interested in mimicking. I loved the softer, wilder touch the co-mingling of spiny and tangly plants offered as opposed to the spotty planting you often see in cactus gardens. Winter is not yet through and how well my hardy cacti have performed remains to be seen. If all goes well, I plan to try something like this again in 2013.
What do you think? What kind of community function do you think these plants perform together? I’d love to hear from any cold hardy cacti (and warm climate, too) gardeners.