Pretty plants with dark motives
More than 800 alien plant species have invaded Canada, more than 400 in Ontario alone.
Most troublesome in this area is garlic mustard. Its hold on top spot is challenged by common buckthorn, with Japanese knotweed, dog strangling vine and the notorious giant hogweed close behind. These plants are mostly seen in wild areas rather than in home gardens, although they will move in where a garden is left untended.
Once upon a time, not too long ago, garlic mustard was not that common, or at least not obvious. Now, it’s one of Ontario’s most aggressive forest invaders. It sprouts on wasteland, especially where soil has been disturbed, and spreads quickly along roadsides, trails and fence lines. I’m keeping an eye on the clumps growing only inches away behind my fence.
Garlic mustard may sound like a perfect condiment, and it has been called the poor person’s mustard. It’s a prolific self-seeder, unthreatened by the insects and fungi that keep it under control in its native habitat — Europe. It even has a negative allelopathic effect by producing chemicals that suppress soil organisms required for optimum growth of native plants, crowding them out. It’s a biennial plant that only produces a cluster of leaves the first year, but in the second year of its short life, this fast spreader flowers and produces hundreds of seeds that can sneak into your garden. A dense population can produce over 100,000 seeds per square metre. Control it by both digging and cutting off the flowers before they go to seed.
Another invasive plant that does stand out is dame’s rocket, often referred to as wild phlox, common in early summer along trails. It’s that tall, pretty plant with the lovely purple and mauve flowers. Pretty it may be, yet it’s a serious menace, posturing as a native flower while quietly intruding into woodlots where it overwhelms spring ephemerals.
These were all garden plants at one time before they escaped to become a serious problem in the wider environment. It’s unlikely that anyone would plant these intentionally in their garden now, but there are lots of other invasive plants like goutweed and lily of the valley being added to gardens and many that are still being sold at garden centres and nurseries.
Typically, they’re recommended as excellent ground covers, and for anyone who has let them run loose in a flower bed, they’ll know they fulfil that role well — too well. It’s when they escape from a garden that the real trouble begins.
In woodlots around the region, it’s common to see periwinkle blanketing the forest floor. To the casual observer not familiar with plants, it looks fine. “What’s the problem? It’s green,” they might think. They see it has rich, glossy, evergreen foliage that nicely hides the grubby soil, and it has beautiful blue flowers. No doubt a few rooted pieces are unknowingly collected and transplanted to a garden to perpetuate the spread.
Near to me is an urban forest where large sections have been completely taken over, where beloved trilliums and other spring ephemerals like trout lily, bloodroot and mayapples once grew. In other areas goutweed is flourishing, crowding out native plants.
Poor wildflowers have no chance when buried beneath a plant that can hide a castle.
For more information on invasive plants, visit the Ontario Invasive Plant Council at tinyurl.com/26p77hyd.