Naturologie: Lawn and Garden weeds, Part 1

My colleagues asked me to write something on lawn and garden weeds. The term weed is subjective rather than botanical, and generally means a plant growing where somebody objects. I will discuss only a few of the worst that I have seen. I judge these ones to be “bad weeds” as they are not native to the province AND they are difficult to eradicate. Generally, ‘weeds’ are plants introduced intentionally or otherwise. Intentional introductions are garden materials brought over by settlers or purchased in a garden centres. Anything labelled as fast-growing, should raise warnings that the plant may become invasive at some point in the future.

This is true of the following three: balsam, goutweed and Japanese Knotweed. All are herbs. Goutweed (Aegopodium podagraria) is a ground-cover, selected because of its attractive green or variegated foliage. It is related to carrot and celery. Once established it is nearly impossible to remove, as is true of many colonial species. However its persistence at present, is limited to cultivated land. It does not seem to spread, yet, into habitats of native flora. Because of this tenacity, it has fallen out of favour with contemporary gardeners who left with legacy plants!

Japanese Knotweed (Fallopia japonica), is another herb brought over by settlers to use as a hedging planting. Its tall hollow stems can grow 25cm a week. Sometimes called ‘bamboo’, it is not. It is related to buckwheat. In part its persistence is due to the 10m rootball that supports the above-ground established plant. This plant has gained notoriety as an Invasive Species because of its spread to beaches and woodlands, displacing the native plant communities in Nova Scotia. I have been asked if it is more common now than previously. Like all invasive species, there is a period of establishment after their introduction. This may take 3 generations, 30 generations or 300 generations. Who knows? What is obvious from the media in western provinces, is that it now actively spreading. This is the second phase of invasion by exotic plants. Nova Scotia has hosted Japanese Knotweed since at least 1944. It was a desirable plant to provide windbreak, hide the outhouse, hedgerows, etc., and probably deliberately introduced for that. I remember it growing at my grandparents’ farm, and my grandmother making a gruel out of the boiled shoots. It was a ‘gruelling’ experience to eat…much like a mouthful of glue! Others use the steamed shoots when very young as a vegetable.

The final herb I will list here is Himalayan Balsam, Impatiens glandulifera. This annual at the moment is spreading from yards where it was planted to roadsides and wasteland. It deserves watching on whether or not it threatens our native plants. Elsewhere it invades floodplains and other sensitive habitats.

As gardeners we need to inform ourselves of the material we are planting. Just because it is available does not mean it is safe from becoming an invader. For information on responsible gardening, there are several helpful downloads available from our colleagues in Ontario.

http://www.invadingspecies.com/invaders/plants-terrestrial/

You will read more here in the coming weeks on weeds that make a difference to our province.