A rogue's gallery of invasive plants

One of my first visits to Point Pelee National Park was in the spring of 1987.

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One of my first visits to Point Pelee National Park was in the spring of 1987. You may know Point Pelee as one of the best places in North America to observe spring birds, and as a beginning birder, I joined a guided walk around the park. Bird identification was the main topic, but I recall the leader paused to point out a plant.

“Here is an interesting plant species that we are just starting to see in Point Pelee.”

That new plant was garlic mustard, a highly invasive species that now grows just about everywhere. Garlic mustard has the redeeming feature of being an excellent addition to spring salads, but it is mainly known as an invasive weed gardeners try to eradicate. If you have a personal list of invasive plants, chances are very good that garlic mustard is on it.

I also wouldn’t be surprised to find goutweed on your list of invasive plants. Goutweed has many names (such as ground elder and bishop’s weed) and is among the most frequently nominated species to be pulled on sight. But you will find a carefully tended and controlled goutweed patch in Stratford’s Shakespearean Garden, because Shakespeare probably knew its white flowers (it is sometimes called “snow-on-the-mountain”) and reputed benefits as a cure for, well, gout. It can also be a tasty table green, especially when harvested young. Visit colorfulcanary.com for a collection of recipes compiled as “If You Can’t Beat It, Eat It.” Despite possible merits, a little goutweed can very quickly become too much goutweed. In my opinion, it belongs on your list.

Dog-strangling vine is an invasive species that seems to have no redeeming features.

Julianne Labreche, an Ottawa master gardener who volunteers at the Central Experimental Farm, describes it as a “wicked invasive.” A member of the milkweed family, dog-strangling vine might appear to be a plant to encourage a possible monarch butterfly habitat, which it is not, because monarch caterpillars will not eat it.

Perhaps the best thing to be said about it is, as Julianne points out, there is no evidence that it has ever actually strangled a dog. A dog-strangling vine can grow as tall as two metres (6.6 feet), spreading very rapidly to create dense mats. Like milkweed, its seeds have feathery tufts that enable them to be widely dispersed by wind. Its roots produce chemicals that discourage the nearby growth of other plant species (a process known as allelopathy which you may know if you have tried to grow anything in the immediate vicinity of a black walnut tree), and new plants can develop from small bits of root left behind in weeding. In fact, it seems generally agreed that the roots can survive for a long time after being pulled, and they should not be added to compost. The recommended best practice is to place pulled plants in black garbage bags and leaving them to “cook” in the sun for at least a few weeks before adding them to landfill.

Dog-strangling vine is a serious problem in parts of Ontario such as Ottawa, where it is widespread on the campus of Carleton University and the Fletcher Wildlife Garden.

Stratford’s parks, forestry and cemetery manager Quin Malott says it has been found in this area, but “isn’t a serious problem – not yet.” He adds that he and his colleagues are concerned about other invasive species, particularly Japanese knotweed and giant hogweed, in Stratford’s Dolan Conservation Area.

Japanese Knotweed is a very tall bamboo-like plant with impressive white flowers. In fact, it was sold as an ornamental species until relatively recently. I can vouch for how difficult it is to eradicate.

Giant hogweed is well-named, with records of plants growing as tall as four metres (more than 13 feet)! Giant hogweed also exudes a very toxic sap that can cause very irritating and painful skin irritations and even blindness.

Try not to make my mistake. When I first saw giant hogweed many years ago in my early days of gardening, I was so impressed that I gathered seeds to plant at home. Fortunately, I consulted a more seasoned gardener who strongly advised against my plan.

In other gardening news, Garden Stratford (Stratford and District Horticultural Society) will meet Monday, Oct. 28, at Stratford’s Festival Inn. Come at 6:30 p.m. to join an informal “Garden Chat” led by master gardeners. Topic: Ornamental Grasses. At 7:30 p.m., we will welcome guest speaker Trevor Barton. Trevor’s topic: Guelph Enabling Garden: Gardens For All. No charge and everyone is warmly welcome.

My great thanks to Julianne Labreche and Quin Mallot. There are many internet resources for more information about invasive species in Ontario. A good place to start is invadingspecies.com.