Last month’s column described some invasive alien plants that should be controlled, and pointed out the difficulties of getting rid of them.
Obviously, preventing them from becoming established is the best defence, but in cases where they have taken hold, removing all of the root system becomes desirable, though often difficult.
One of the more common ways whereby invasive species are introduced is by careless disposal of garden wastes, and lamium (or deadnettle), which is often used in hanging baskets and thrown out at the end of the season, is amongst the worst. It grows rapidly in a wide range of habitats, is not eaten by deer or rabbits and, unfortunately, is sometimes recommended for ground-cover planting.
Lamium is comparable to English ivy in its ability to spread and overwhelm native vegetation, thus creating local monospecific stands with much reduced biodiversity.
Up-rooting, repeated over several seasons, is the optimum, though laborious, control.
English ivy has a low-growing form that provides complete, spreading ground cover excluding other plants and an arborescent form that can climb to 50 metres on any supporting structure or tree where its weight risks breakage. It does not feed off the tree but simply uses it for support.
Again, up-rooting is the best control, but severing the basal stem of climbing plants is also effective.
If you decide to plant ivy at all, be sure to use only the low-growing juvenile form.
Like lamium, spartina (or cord grass) is a damaging, habitat-altering invader. It was introduced here from the east coast of North America as packaging for oysters and is slowly but steadily changing productive mud flats into rather sterile marshes inimical to shellfish, juvenile fish and shore birds all along the coast of the Pacific Northwest.
It can also clog estuaries and recreational beaches. It is now present on the shores of Mud Bay and Boundary Bay, so important for resident and transient shore birds, and the environmental group Friends of Boundary Bay organizes summer work parties – Beach Heroes – along with City of Surrey’s SHaRP summer programs to remove spartina in an effort to preserve the ecological integrity of the shore-line habitat.
A study on nearby Washington’s Wallapa Bay is showing how rapidly it can spread; there, in 1992, it covered 400 acres and the area almost quadrupled to 15,000 acres by 2002, a dramatic indication of the need for control.
Hand-pulling and digging are the recommended control measures.
Some other undesirable aliens – all capable of rapid spread and habitat impoverishment – are the unpleasant-smelling herb robert, morning glory, periwinkle and purple loosestrife, which can be checked by cutting the stems before flowers have gone to seed and by promoting the two known leaf beetles and three weevils that feed on it.
The Ministry of Food and Agriculture’s website – www.agf.bc.ca/cropprot/nonnativepests.htm – deals mainly with diseases and insects, but it has a useful link to undesirable plant introductions also.
It’s evident that, once established, these invasive plants are difficult to eradicate and so the old cliché applies: prevention is better than cure; don’t plant them.
Dr. Roy Strang writes monthly on the environment for the Peace Arch News. rmstrang@shaw.ca