Bête noire is a delightful term that I picked up in my government French-language training course many decades ago. It literally means “black beast” and is used to describe something or someone that provokes strong dislike or is a recurring source of frustration or fear in one’s life

What is your gardening “black beast”? Goutweed invading your prize perennials? Bindweed popping up all over your lawn and vegetable patch? Poison ivy creeping into your garden under the neighbour’s fence?

It’s a tough choice, but my vote goes to goutweed. Although, in my experience, bindweed comes a very close second.

There are two forms of goutweed — a variegated version and the all-green one. If tightly controlled (for example, between a house foundation and a sidewalk), it can be quite attractive, but it has to be watched carefully as it spreads rapidly. Once established, it is nearly impossible to eradicate. The smallest piece of rhizome left in the ground will quickly form a sturdy new plant. The primary vector for dispersal to new areas is human plantings as an ornamental, medicinal or vegetable plant.

The creeping bellflower is another thug that comes into gardens disguised as an attractive perennial plant. It was introduced from Europe as a garden flower. Its blue flowers are commonly seen around town in gardens. Any piece of its white creeping root (rhizome) or its tubers will send up a new plant.

So, how do these annoying plants get into our gardens?

For some, “the answer is blowing in the wind”. Others arrive in a cubic yard of topsoil delivered to your driveway. I have seen a new garden full of a witches’ brew of six or seven of the most invasive weeds that a gardener can imagine. I always try to buy locally from sources that I trust.

Some weeds are there because we failed to do adequate preparation. I always stress the importance of knowing what types of weeds you are digging out when you are preparing your planting beds. For example, dandelions have a long taproot — if you are able to get the whole root the plant will not come back — however, any piece of root left in the ground will regenerate. Perennial grasses are difficult to eliminate as they have long horizontal roots that may stretch half a metre or more. A rototiller will break those roots into little pieces, every one of which will send up a new plant.

Some bêtes noires are there because of unintended consequences of our plant choices. A few decades ago, I tried to grow several types of herbal and medicinal plants. Some of those plants rewarded my care and nurturing by growing tangled clumps, spreading rampantly, or flowering profusely and spreading their seed far and wide. Comfrey (Symphytum officinale) is a very large perennial plant with a branched root that mines minerals from the subsoil and whose foliage can be used to make a manure “tea”. However, if allowed to go to seed, little plants spring up all over the place and in no time at all turn into monsters. Stinging nettle (Urtica dioica) has been widely used as a medicinal plant and as a culinary plant. It is a bit of a spreader, and the roots are truly a wicked tangled web. Tansy (Tanacetum vulgare) has been traditionally used as an insecticide and disinfectant. It produces huge amounts of seeds that sprout readily.

Your choice of garden style may not be appropriate to your approach to gardening. An English country garden chock-a-bloc with perennials may require more maintenance than you are prepared to give. On the one hand we want plants that will thrive, on the other hand we want plants that will be well behaved. Our relationship with plants is a complicated one. We think that our new perennial border will be maintenance-free; however, any garden requires a lot of work.

The primary vehicle for the spread of many invasive plants is the automobile! Gardeners plant many invasive plants because they are very attractive. Japanese knotweed, for example, was introduced to North America as a horticultural plant in the late 19th century. It is a very attractive structural plant, resembling bamboo, but is tough to confine.

So, how does one avoid garden nightmares? The first stage is education. The more you know about plants, the better positioned you are to repel invaders. Research plants before you welcome them into your garden. The best control is to not plant it in the first place; or if you must plant it, ensure that it is safely confined.

So, what is one to do if one has a patch of goutweed or Canada thistle that one wishes to get rid of? Attempts to control goutweed in a garden with landscape cloth, bark mulch, and hand weeding are largely unsuccessful. We no longer use chemicals, and it is impossible to dig them out (unless one uses a backhoe). One solution I have used with considerable success is to cover the patch of ground with a heavy black plastic sheet — with a plant such as goutweed it may be necessary to leave the plastic cover on for a full growing season. Some plants such as bindweed can be dealt with by cutting every stem that rears its head. Eventually the plant may lose the will to live.

Not all plants that cause us grief are officially classified as invasive. The Ontario Invasive Plant Council defines invasive plants as species introduced outside their natural range that pose risks to the environment, economy, or society. In Ontario, these plants can disrupt forests, wetlands, lakes, rivers and agricultural lands, outcompete native species and alter habitats.

Much more information is available from the Ontario Invasive Plant Council ontarioinvasiveplants.ca. Further resources include Landscape Ontario, Conservation Authorities and the Ontario Government.