Gardeners ‘crucial’ in avoiding spread of non-native species

Gardeners and horticulturalists have a key role to play in helping stem the spread of invasive plants this autumn, a national trade body has said. 

Experts at the Property Care Association (PCA) are encouraging gardeners to identify and contain any non-native plants to ensure they can’t escape into the wild. 

The Association has issued a series of tips to help gardeners manage the spread of ornamental plants, and ensure they don’t become a nuisance in the future. 

Dr Peter Fitzsimons is technical manager of the PCA’s Invasive Weed Control Group. He 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 as garden ornamentals but have taken-off to some degree or other in to the wild and are now included in 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 – and gardeners have a crucial role to play as we go into winter.” 

Dr Fitzsimons advises gardeners and horticulturalists to include the following in their autumn jobs list: 

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 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 a suitable stump treatment applied to suppress re-growth (please consult your local garden centre for advice). 

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