Research

Conservation & Environment Guideline Leaflets

Invasive non-native species

Our gardens have been greatly enriched by the introduction of plants from abroad but a small number have proved highly invasive in the wider environment, threatening natural habitats and native species. The control of these species is difficult and costly, yet many are widely available with little indication of the damage they can do if they are allowed to escape into the wild or disposed of carelessly. The Royal Horticultural Society does not wish to see the diversity of plant material available to the gardener restricted but recognises that the threat to native species and habitats from these plants is serious.

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A summary of RHS policy

1) The RHS recognises that while a few non-native species have proved highly invasive and threaten native habitats, the vast majority of the many thousands of plants introduced into the UK have greatly enhanced gardens and provided the basis of an important commercial horticultural industry.

2) The RHS provides information to gardeners about actual and potential invasive non-natives, their control and the danger to native habitats of releasing invasive species into the wild.

3) The RHS supports and urges the horticultural trade and gardeners to follow the Horticultural Code of Practice to prevent the spread of invasive nonnative species.

4) The Society believes that a national body should be charged with the responsibility, and given resources, for monitoring and evaluating potentially invasive plants and the co-ordination of their control.

5) The Society does not want to see a situation where gardeners are criminalised for inadvertently allowing plants to escape from their gardens.

6) The Society does not stock the invasive plants listed below in its plant centres and since 2004 has operated a policy to prohibit exhibitors from selling or showing these plants at RHS Shows: Himalayan balsam (Impatiens glandulifera), giant hogweed (Heracleum mantegazzianum), Japanese knotweed (Fallopia japonica), fairy fern (Azolla filiculoides), New Zealand pygmy weed (Crassula helmsii), parrot’s feather (Myriophyllum aquaticum), floating pennywort (Hydrocotyle ranunculoides).

7) The RHS deplores fly tipping and other inappropriate means of disposing of unwanted garden plants and weeds; and recommends composting or disposal through local authority waste disposal centres. The release of non-native animals, other than approved biological controls, is also an unacceptable practice.