Butterfly bush Buddleja davidii (above) is a species originating in China, introduced to the British Isles in 1896, but not found outside gardens until 19224. It "discovered" a vacant niche, as a shrub capable of living on brickwork and rubble and in brownfield sites.
It is considered a problem invasive species by ecologists, but is so firmly established that it's inconceivable that it could be eradicated, so there is no real reason not to allow it to appear in your garden.
Not only is it eponomously popular as a nectar plant for butterflies and moths, it supported 19 species of moth caterpillars, more than any other plant in Jennifer Owen's garden5.
We have two web pages about native versus non-native planting. “Gardens: native and non-native species” covers the science, and “Should you only grow native plants?” covers the practical aspects, so detailed arguments need not be repeated here. The first evidence that non-native plants can be beneficial was the simple fact that Jennifer Owen’s garden, containing a typical mix of native (38%) and non-native species (62%) was bursting with wildlife5. Owen’s work prompted the Sheffield University Biodiversity in Urban Gardens in Sheffield (BUGS) project, which remains globally unsurpassed as a thorough examination of garden biodiversity. This careful study failed to find any link between the variety and abundance of native plants in individual gardens and that of the animal species in the same gardens.
The WLGF was involved in designing the Royal Horticultural Society’s Plants for Bugs (P4B) project. This was the first experimental study of garden biodiversity, aimed at assessing the value of non-native plants compared with natives. Five scientific papers have come from the study so far and the results are clear:
• For pollinators, planting a mix of flowers from a variety of origins was best, and
the more flowers the better – making some cultivars better than the original
• species from the northern hemisphere, closely related to our own flora, were
nearly as good as native species for herbivores, and for detritus-eaters, origin
• Long-established non-native plants had more insects associated than new
• Some insect species (9-32%) were only found on non-native plants, which
represent a new resource for some otherwise rare native insects9
• Exotic species from the southern hemisphere prolonged flower resources for
pollinators into late summer and supported more ground-dwelling invertebrates
• Most importantly the studies showed the denser the vegetation, the better for
most invertebrates – regardless of where the plants came from7
Although you may choose to plant only native species in your “wildlife garden” you really don’t need to. Typical gardens planted for pleasure using non-natives are excellent. There are lots of myths perpetuated in wildlife gardening books, so it has been good to dispose of that one.
1. Some species such as the tree bumblebee are known to have arrived recently under their own steam, so are “new natives” It is likely that many other plant and animal species also arrived in the last seven thousand years without human help, but we can’t know for certain.
2. Nottridge, R. 2009 Wildlife Gardening The Crowood Press
3. Kirk, W.D.F and Howes, F.N. (2012) Plants for Bees. A Guide to the Plants that Benefit the Bees of the British Isles. International Bees Research Association
4. Stace, C.A. and Crawley, M.J (2015) Alien Plants. New Naturalist Library Collins.
5. Owen, J. 1991. The Ecology of a Garden, the first fifteen years. Cambridge University Press.
6. Salisbury, A., Armitage, J., Bostock, H., Perry, J., Tatchell, M., Thompson, K. (2015). Enhancing gardens as habitats for flower-visiting aerial insects (pollinators): should we plant native or exotic species? Journal of Applied Ecology 52:1156-1164.
7. Salisbury, A., Al-Beidh, S., Armitage, J., Bird, S. , Bostock, H., Platoni, A., Tatchell, M, Thompson, K. and Perry, J. (2017). Enhancing gardens as habitats for plant-associated invertebrates: should we plant native or exotic species? Biodiversity and Conservation
8. Salisbury, A., Al-Beidh, S., Armitage, J., Bird, S., Bostock, H., Platoni, A., Tatchell, M., Thompson, K. and Perry, J. (2019). Enhancing gardens as habitats for soil surface-active invertebrates: should we plant native or exotic species? Biodiversity and Conservation 29,129–151
9. Padovani, RJ, Salisbury, A, Bostock, H, Roy, DB, Thomas, CD. (2020) Introduced plants as novel Anthropocene habitats for insects. Glob Change Biol; 26:971– 988. https://doi.org/10.1111/gcb.14915
Page written by Steve Head: Reviewed by Ken Thompson.