Invasive Plants | Sunnyside Acres Heritage Society

Sunnyside Invasives

So-called ‘invasives’ are plants which have been introduced from elsewhere and are proliferating to such an extent that they threaten to alter the local environment and the survival of native species. Himalayan Blackberry is probably the most widespread and well-known but Japanese Knotweed is more harmful and also more difficult to remove or even control.

Himalayan Blackberry [a.k.a. ‘bramble’] is one of several Rubus species which include the native salmonberry, thimbleberry and trailing blackberry. The introduced Himalayan Blackberry has strong, often angular , fast-growing stems armed with sharp, re-curved thorns. The toothed leaves vary being 3-lobed on flowering stems and 5-lobed on vegetative ones; all are green on the upper side and covered with whitish hairs on the underside. The fruit, black when ripe, is edible and tasty. Removal calls for excavation of the extensive root system, possibly over more than one year, and perhaps application of the weedkiller, glyphosate, to young shoots in spring.

Of the several knotweed species found in B.C., Japanese Knotweed is the most damaging and it is very difficult to eradicate once established. It is a fast-growing, semi-woody perennial with hollow stems, almost bamboo-like although they are not related. Stems have red-brown speckles, papery sheaths and conspicuous nodes from which juvenile stems arise. The leaves are heart-shaped or triangular, 10 to 15cm wide and 15 cm long arranged in a distinctive zig-zag pattern along the stem. They are reddish in spring and the bare winter stems are erect and gray.

Mechanical control requires repeat excavation of roots of Rhizomes for several years since even small residual sections of Rhizome can grow up to 8 cm per day. The optimal chemical control is direct injection of chemical weed-killer at the base of the stem. This very aggressive plant can quickly form dense monoculture stands and create a thick litter layer which inhibits all other plants. The Rhizomes can penetrate asphalt, brick, and concrete, so that it can be structurally as well as biologically harmful.The related giant and Himalayan Knotweeds are also present but have not been recorded in the vicinity of Sunnyside Acres Forest, at least not yet.

The small, inconspicuous but persistent geranium, Herb Robert, can be troublesome in gardens and grows along paths and trails in Sunnyside. Its leaves are small, 3 to 5 cm, egg-shaped and deeply divided. Flowers are usually pink with white stripes and bristle-like sepals. It has a rather unpleasant smell.

English Ivy is a vigorous and aggressive perennial vine which has both a juvenile, ground trailing form and an arbores cent, climbing form. It can develop dense, smothering ground cover and, just by eventual weight, cause trees to break or topple. Lower leaves are lobed, dull green above and lighter on the underside, about 15cm across. Because it causes harmful habitat change it should be removed or at least controlled wherever it is found and discouraged in gardens

Lamium, sometimes called ‘dead nettle’ because it doesn’t sting, is a spreading ground cover plant which produces several angular stems from its base. The opposite leaves are heart-shaped, shallowly toothed and distinctively coloured being green along the edges and in a large part of the centre and white elsewhere. Stems are angular. Lamium spreads vigorously but is relatively easily up-rooted. When discarding garden plants, take care not to introduce Lamium into natural areas.