Things to look out for in the garden - garden invaders and how to avoid spreading them

Did you know that many familiar British plants have actually been introduced from other countries, some many hundreds of years ago, which has resulted in invasive species spreading so rapidly, they out-compete the native vegetation. They're not easy to control by the acceptable herbicides such as glyphosphate, and clearance programmes are costing vast sums - up to £300 million nationally to tackle Himalayan balsam for example. It has become such a huge problem, that it's illegal under the Wildlife and Countryside Act 1981 to introduce certain species into the wild.

1. Japanese knotweed - introduced for ornamental planting in the 19th Century, it was first recorded in the wild in 1900. There are four species running wild in the UK: Himalayan knotweed, Indian knotweed, Giant knotweed, and a hybrid between Japanese and Giant knotweed. They are all mainly female which means that the spread is vegetative - any portion of root as small as the tip of the little finger can produce a new plant.
2. Giant hogweed - the damp-loving and architecturally stunning giant hogweed is a perennial which can grow five metres high. It has become infamous because it can cause painful blisters, with resulting skin discolouration that can last up to six years.
3. Australian swamp stonecrop - The tiny Australian swamp stonecrop (also known as New Zealand pigmyweed) is spreading in local ponds and other slow moving water-bodies. This plant is a small succulent and has three different shapes depending on whether it is terrestrial, emergent or submergent. Once established, it can spread from minute fragments, smother native plants and quickly take over.
4. Water fern -The water fern is a Latin American introduction and has a delicate appearance with its small red curled fronds, but will quickly cover the surface of any water body completely. It's a stealth plant too, in the winter it can avoid detection by sinking to the pond bottom.

So remember - don't dump garden waste in semi-natural habitats - it's stupid and illegal. Compost garden waste or take it to a recycling centre.

Garden stonecrop photograph by Eggy Bird, used under a creative commons attribution licence.

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