The "Big Three" Invasive Weeds are Waking Up!
Updated: May 12
Invasive weeds species to look out for in early Spring
As we enter Spring, invasive weeds are beginning to show signs of life. So what should we look out for, that would indicate the presence of invasives on a site? Here are a few examples of the “big three” spotted during recent site inspections in Edinburgh and Glasgow.
Japanese Knotweed (Reynoutria japonica)
After last season's growth has died back over Winter, the distinctive creamy to dark brown, bamboo-like hollow canes may still be evident. These can be between 2 – 3 metres in height, brittle and easy to break, and the canes have distinctive node rings at regular intervals.
Come Spring, pink buds and nodules begin to emerge from the crown (dense above-ground protrusion at the base of the stems). Avoid disturbing these as Japanese Knotweed can easily regenerate, so fragmented crowns can result in spread to other areas.
Himalayan Balsam (Impatiens glandulifera)
This plant is often found growing along riverbanks and in moist areas. A good way of identifying a possible stand of Himalayan balsam is to look for the creamy straw like remnants of the previous year’s stems strewn across an otherwise relatively bare patch.
The early seedlings that appear at this time of year are very different to the true leaves that appear later (thinner, longer and pointed). Pairs of symmetrical oval to rounded leaves with central venation appear on delicate single stems.
Giant Hogweed (Heracleum mantegazzianum)
Spring sees Giant Hogweed seedlings rapidly emerging across a range of environments from riverbanks to brownfield land and other vacant sites. Early true leaf growth currently looks like smaller, more prostrate versions of the mature plant: Sharply divided, angular and jagged leaves with bristles.
As the plants develop, hollow, purple to red speckled stems start to develop, becoming more serrated looking. Remnants of previous years tall fluted hollow canes and distinctive umbrella like flower heads often evident also.
Avoid contact with Giant Hogweed as the plant causes photosensitivity, leading to skin blistering when exposed to sunlight. Unfortunately there have already been cases in the news of people and animals suffering injuries after coming in contact with the plant.