Trade body appeal to tackle invasive plants in autumn

[November 2018]

A national trade body is urging horticulturists and gardeners to help stem the spread of invasive plants as part of their autumn maintenance regime.

Experts at the Property Care Association (PCA) have produced a series of tips to help contain a range of non-native weeds and prevent their potentially damaging spread.
The advice is part of ongoing work from the PCA to raise awareness of the issue, which included an award-winning garden of invasive plants at the RHS Chelsea Flower Show earlier this year.

The ‘Enemy Within’ garden showcased 14 of the non-native plants which are currently thriving in gardens across the country – with the message that the next Japanese knotweed could already be taking hold in UK gardens, providing future generations with a significant ecological, environmental and economic burden.

Dr Peter Fitzsimons, the technical manager of the PCA’s Invasive Weed Control Group, said: ““Invasive non-native plants come in many different forms and sizes.

“Plants including Japanese rose and Montbretia might be a common sight in gardens across the country, but they are among a number of non-native species, including Japanese knotweed, that ‘escape’ from gardens up and down the UK.

“Most started out life as garden ornamentals but have taken off to some degree or other in to the wild and are now covered by Schedule 9 of The Wildlife and Countryside Act 1981.

“This requires them to be managed and controlled to minimise their potential negative impacts on natural ecosystems.

“The message on the need to control such plants was well-received at the RHS Chelsea Flower Show and now we want to continue with this awareness campaign as we go into winter, to keep the issue at the forefront of the minds of horticulturists and gardeners.

“There is much they can do to help in this area, not just in the summer months.”

Guidance from the PCA includes;

Annual plants, with seeds dispersed by wind e.g. Himalayan balsam.
Most plants will already have dropped their seeds by now but where at all possible try to remove seed heads by dead-heading before this happens (don’t put on the compost heap). Seeds present in the soil will germinate in the spring but try to remove these by pulling/hoeing. Alternatively, for those wanting to enjoy the flowers, keep the dead-heading going for a few seasons and the number of plants should decrease dramatically over time, as the seed bank in the soil diminishes.

Perennial (woody shrubs) plants that produce seed attractive to birds etc. (e.g. cotoneaster, Japanese rose).
These plants can be kept in check by pruning and thinning and this will often do much to remove seeds and fruits that can be dispersed by animal vectors. It may seem a bit perverse to deny wild birds a readily available food source for the winter months but the potential harm these plants can cause in the wild should not be underestimated.

Perennial plants that spread by underground rhizomes, stolons or bulbs e.g. Three-cornered garlic, Montbretia, Variegated yellow archangel.
Each year these plants should be lifted and thinned taking great care to sieve the soil to remove excess bulbils etc. The main challenge here is to avoid unintended dispersal outside the garden through the disposal or transfer of soil which still contains the bulbs and root fragments or, in the case of Variegated yellow archangel, stems and stolons which can self-propagate.

Perennial plants; seeds dispersed by wind e.g. Buddleia.
Strictly-speaking Buddleia is not a ‘Schedule 9’ plant nevertheless it is non-native and causes both ecological displacement and can affect buildings and built structures. Seed dispersal can be limited by removing seeds heads in the autumn (bagged and placed in the correct bin) and mature plants can be pruned heavily each winter. If complete removal is needed the plant can be cut down to the ground and ‘Ecoplugs’ or similar applied to the stump (please read label precautions before use) stopping new shoots appearing in the spring.

To further help horticulturists and gardeners make informed decisions, the PCA has produced a book ‘Practical Management of Invasive Non-Native Weeds In Britain and Ireland’ offering detailed insight into 38 plant species individually.

The vast majority of the plants featured derive almost exclusively from species listed in Schedule 9 of the Wildlife and Countryside Act and others of concern to the European Union in the EU Invasive Alien Species Regulation 2014.

More details here.

A video showing the background to the ‘Enemy Within’ garden can be viewed here.