Invertebrates are some of the most useful animals to have in the garden, and a Royal Horticultural Society study has shown that native plant species in the UK support more invertebrates than plants from other regions. Plants for Bugs is a four-year study into wildlife gardening, which was undertaken at RHS Garden Wisley in Surrey, UK.
Wildlife gardening is as much about growing plants as putting up bird boxes or bug hotels. But what type of plants to use has been confusing. The RHS study looked at the question of whether the geographical origin of a garden plant is a significant factor in biodiversity richness. An average garden in the UK contains around 70% non-native plants to just 30% British native plants. Data from the Plants for Bugs study is beginning to reveal if there are any recordable differences in invertebrate numbers and species between these plant groups.
Plots were planted in 2009 with species from three geographical zones – the UK (native), the northern hemisphere excluding the UK (non-native – northern), and the southern hemisphere (non-native – southern). Each contained a mix of 14 species of plants, including bulbs, perennials, shrubs, grasses, ferns and a climber, and designed to be typical of a small garden border.
By the end of December 2013 (four full years of recording) approximately 80,000 invertebrates had been counted and more than 300 species identified. Two peer reviewed papers have been published, looking at the results from the pollinating insects and invertebrates that live on the plants.
The results and recommendations for gardeners have been published in two interpretation bulletins:
Bulletin 1 Gardens as Habitats for Pollinators in August 2015, and more recently
Bulletin 2 Gardens as Habitats for Plant-dwelling Invertebrates, in August 2017.
The significant messages for gardeners from Paper Two, which deals with plant-dwelling invertebrates, are:
- Plant a predominance of plants native to the UK.
- Planting schemes that are based on plants originating from the northern hemisphere (near-natives) may support only marginally fewer (less than 10%) invertebrates in some functional groups (including herbivores and some predators) than UK native plant schemes. Plant schemes based on southern hemisphere (exotic) plants will still support a good number of invertebrates, albeit around 20% fewer than plants from the UK.
- Regardless of plant origin, the more densely a plant scheme is planted or allowed to grow, the more invertebrates of all kinds (herbivores, predators, detritivores and omnivores) it will support.