Fighting an aggressive weed made me realize my garden is full of invasive species

Goutweed. It's a word that strikes terror into the heart of every gardener.

Also known by the more marketable names "ground elder" and "snow on the mountain," goutweed was brought to North America from Europe only to spread out of control in its new surroundings.

The aggressive ground cover is so resistant to removal it's been called "the cockroach of the botanical world," and my backyard is full of the stuff.

Actually getting rid of this much goutweed would require a level of landscape warfare I can hardly imagine, let alone afford: excavating the entire yard to a depth of two feet, replacing the soil, and installing a metal-lined trench around the perimeterto prevent new incursions.

So instead I'm planning to adopt a proxy war strategy by enlisting better-behaved flowers to outcompete the goutweed. The only problem? All the prime candidates for my campaign like bigroot geranium, wild gingerand sweet woodruff are introduced species, too.

It turns out almost nothing in my garden, from trees to weeds, is native to Newfoundland.

When my spouse and I bought our little house in St. John's, we inherited a mature yard shaded by Norway maples and scented with Persian lilacs.

We water the Chinese peonies and Welsh poppies, and every May we hold off on mowing the Kentucky bluegrass so the dandelions can bloom and feed local pollinators.

In my quest for hardy perennials that will thrive on neglect and our two weeks of annual sunshine, I've added Asiatic lilies, English lavenderand American boxwoods to our garden patch.

I'm playing host, in other words, to a UN summit of plant life, and it isn't just me. Most plants you'll find around town aren't indigenous to the island.

So how did non-native species come to take over our gardens?

Plants can be introduced to new habitats accidentally, transported in livestock feed or carried by migratory birds. Most alien species in Newfoundland, however, were brought here intentionally by settlers.

Some, like turnips, cabbages, and apples, were imported as food crops while others, like the demon goutweed, were probably taken along for their medicinal properties. (As the name suggests, goutweed was used to treat joints swollen from gout or arthritis before the advent of anti-inflammatory drugs.)

Many introduced species, though, had a purely esthetic appeal.

Early European settlers packed up the seeds of familiar trees, shrubs and flowers to recreate the gardens they had enjoyed in their native countries.

The result was a kind of colonization of the landscape. With their plantings, settlers reshaped Newfoundland and other parts of the Americas into an environment that resembled Europe, where they were more and Indigenous peoples less at home.

The situation snowballed in the 18th and 19th centuries. Newly established botanical gardens acquainted North Americans with plants from all over the world, and soon garden centres popped up to provide the most attractive and robust species to the home gardener.

The majority stayed where they were planted, but the most vigorous varieties hopped garden fences and soon overran field and forest.

Our province'smeadows offer a stark example. Many of Newfoundland's most iconic wildflowers weren't here 500years ago.

Lupins, daisies, clover, devil's paintbrush, even the forget-me-nots that have been used as a symbol of remembrance in Newfoundland since the First World War all were introduced to the island with colonization.

Now, invasive species aren't all bad.

Lupins and clover enrich the soil by converting nitrogen gas into solids.

Norway maples are better able to withstand threats like air pollution and road salt than native maples, making them robust choices for an urban forest.

In other parts of the world, non-native plants have even supported the recovery of endangered bird populations.

By and large, though, introduced species aren't as beneficial to local wildlife as the native plants that evolved alongside them.

Those dandelions that spring up on my lawn during No-Mow May? They're Eurasian imports and less nutritious for our bees and butterflies than indigenous alternatives like marsh marigolds and Joe Pye weed.

Certain introduced plants are prized by gardeners precisely because their blossoms and leaves are unpalatable to native insects. They may not get riddled with unsightly holes, but they also won't support thriving populations of bugs and further up the food chain birds, bats, foxes, and bears.

Non-native garden plants have other environmental costs, too, often requiring more watering, fertilizingand mowing than native shrubs and grasses.

Perhaps the greatest problem with introducing plants to new environments, though, is the most ephemeral one: the reduction in biodiversity.

Trade in garden plants is making environments around the world more and more similar to each other. In an era of rapid climate change and species extinction, that could have dramatic consequences.

Diverse ecosystems are more adaptable. If one species dies off, there are others to take its place.

If only a handful of species fill the same ecological niche worldwide, on the other hand, and one goes into decline, ecosystems have fewer opportunities for recovery.

In my yard, the goutweed has choked out all opposition. There's no indigenous plant that can keep it in check.

Even if there were, none of the local nurseries sell native ground covers anyway, and most of their customers, like me, don't even know the difference.

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