How does your garden grow?

The warming climate provides an opportunity for Cottage Country gardeners to take some planting risks. Peaches, anyone?

by Mark and Ben Cullen

Climate change is here, whether we like it or not. But, of course, this isn’t new information.

The long-term warming trend is indeed reshaping how we garden, and while we don’t really like the overall trend (and, in fact, support measures to curb it) we also accept there’s a certain level of warming which is, at this point, locked in.

Lavender

With the effects of climate change, we’re more likely to experience hot summer droughts and extreme cold conditions in winter, shifts that can kill many plant species that haven’t yet adapted. But what does this mean for gardeners, especially in Ontario’s Cottage Country?

Kevin Kavanagh is someone who has spent a lot of time thinking about this very issue. After a career as a conservational biologist with World Wildlife Fund Canada and the Nature Conservancy of Canada, Kavanagh established South Coast Gardens in 2005 near the shore of Lake Erie in St Williams, ON.

South Coast is a small nursery that specializes in native and rare species, some of which, historically, have been only marginally hardy in our climate. In a phone conversation with us, Kavanagh addressed the issue of climate change head-on. “I think we can all accept that global climate change is happening. There’s no doubt about it, the world is getting warming, and, generally speaking, more extreme weather is occurring. We don’t escape the wild swings that provide some of the coldest weather, but there are new opportunities for plant species.”

New growing zones for Cottage Country

The opportunities to which he is referring are for those plants which we haven’t, historically, considered hardy, based on the old USDA growing zone maps.

“There are published reports that look at how zones are shifting,” Kavanagh explains. “In the past 30 years, these zones have shifted northwards about 150 to 200 kms. The new Canadian system is trying to match up with the USDA system, but for now you could try going a half-zone higher than you’ve tried in the past.” That means Kawartha, for example, historically a USDA zone 5a, is now a 5b.

Until recently, we would not have recommended most yew (taxus) varieties for planting here, but now they thrive, especially when they are planted out of prevailing north or west winds. The same can be said for apricots, certain peach varieties and many herbaceous perennials like coreopsis, Shasta daisies, meadow rue and lavender.

Shasta daisies

Help marginal species adapt

Growing a tree or shrub outside of its traditional growing zone is never as easy as dropping it in a hole and forgetting about it. But here are some tips that should help:

Start by selecting a local seed source: “Shipping plants from the deep south probably isn’t going to work for us,” says Kavanagh. “Native sweetgum trees (Liquidambar styraciflua) from seed sources as far north as Indiana have been shown to do well in our part of Ontario as the genotypes are more locally adapted to severe weather than the populations growing further south.

Protect from wind and sun: In late autumn, place a screen of white fabric around plants without wrapping too tightly. A cheap set of white sheets will suffice. The white fabric is preferred as is deflects the winter sun, which can actually burn plants, while protecting against wind.

Create a microsite: By planting simple barriers such as evergreens (or a fence) to the west and north of your home, you’ll create a microsite, a protected area on the east side for planting tender varieties. When you have a choice, plant in east- and south-facing locations and near the wall of a permanent structure. The protection provided can be a full zone warmer than the one in which you live.

Mulch adequately and water evergreens deeply in the fall: The freeze/thaw cycle can be particularly damaging with warm spells followed by cold snaps, an occurrence that’s increasingly common. White plastic tree guards can prevent bark split or sunscald during early spring warm spells.

Take risks: Experimentation is half the fun of gardening. Nobody knows exactly what the new climate holds, and, as Kavanagh explains, “plants can often surprise us.”

And finally: Long ago, we accepted certain failures as a part of the overall gardening experience. Of course, it helps to have some knowledge, but pushing the envelope on the issue of plant zones can be fun if considered from this point of view. And with success comes the opportunity for bragging rights in the community, perhaps as the only grower of trees that actually produce peaches.

Mark Cullen is a Member of the Order of Canada. He reaches over two million Canadians with his gardening/ environment messages every week. Ben Cullen is a professional gardener with a keen interest in food gardening and the environment and is the owner of Cullen’s Foods.