I teach COG’s Organic Master Gardener course. In it, we cover the science behind organic land care, which is defined as the design, construction and maintenance of landscapes using practices and products that preserve and support the health of ecosystems and human communities.
- plant adaptations in ecosystems,
- the soil ecosystem,
- soil testing and fertility management, and much more.
The course also prepares students to write the Society of Organic Urban Land Care (SOUL) exam for Accredited Organic Land Care Practitioner, an important certificate for those who aren’t able to obtain organic certification for the land on which they work.
When educating people on the value of native plants vs. alien (or non-native) plants, I’m often asked, “Why are we allowing these imports, if they are so dangerous to our natural environments?”
Our history of moving plants around the world, in the name of ‘collecting’, is a hard habit to kick, and a ban on importing plants is highly unlikely. Indeed, nature moves plants around the world all the time, via animals, wind, storms, etc.. but at what consequence?
New plant varieties may be more pleasing, but pleasing for whom, exactly? Dr. Doug Tallamy, Chair of Entomology and Wildlife Ecology at the University of Delaware, and author of Bringing Nature Home, says that selecting for ornamentals creates fragmented, vulnerable, and less diverse populations of microbes, insects, birds, etc., that are more prone to local extinction, in part because of the potential for diseases without natural competitors to be introduced. He has argued that aliens are relatively poor at supporting other local life forms, including soil microbe communities unique to the local environment. In other words, there is no ecologically equivalent choice because planting aliens puts biodiversity –an essential and non-renewable natural resource—at risk.
The landscaping industry is seeing an increased demand for natives. How is it responding? It is now estimated that approximately 75% of “native” plant varieties for sale in Ontario have been grown in Ecuador or Holland—and only 6 to 10% are actually produced within the 100 km mile radius defined as native by the North American Native Plant Society (NANPS). Can plant varieties produced in Ecuador really be considered native, if they are propagated from stock obtained in Oregon? Will these so-called native plants do well in Collingwood, Ontario?
Current research is trying to answer such questions. So far, Ontario Ministry of Transportation plantings along highway corridors are demonstrating that plants bred in the region and not from afar fare significantly better than imported plants of the same variety. However, this result may just demonstrate regional adaptability, since native plants are not being used. Why not natives? Aliens are often more adaptable, quickly establishing themselves on these sites, where soils are often bare and/or disturbed due to construction activity. So aliens are clearly doing Nature’s bidding, but can become invasive, disturbing the local ecology.
This topic is fraught with complex, ethical questions and demands more investigation and education. When is it right to not plant a native? What to do particularly for challenging city or highway environments? Are there alternatives?
At the University of Guelph test gardens, I saw new Nativar (new cultivars crossed with native species) varieties of our native Asclepias tuberosa (butterfly weed) loaded with Monarch butterfly caterpillars! So it seems we can breed our natives in such a way to preserve ecosystem service integrity; more research is needed, however, to know if Nativars can support diverse communities similarly to their native cousins.
Ultimately, planting motivations should centre on biodiversity and protecting the genetics of our natives so as to continue to support our local ecosystems including plants, birds, insects and microbes. Perhaps we can be persuaded to pause and to research choices better, asking, “Will this choice of alien species best support the environment?”
Our challenge in being involved in evolving our local ecology is to know when to be open to responsible to the introduction of aliens that may eventually become the new natives (indeed, many of our present weeds are aliens which we now call wildflowers). Let’s work closely in this effort with our local, native plant growers. Get to know your native plants better, using the North American Native Plant Association Database!
 Society of Organic Urban Land Care Standard, 6th Edition