RHS establishes link between dense garden plantings and invertebrate wildlife

Gardeners wishing to support plant-dwelling invertebrates such as ladybirds and spiders, should put in more native plants and keep gardens less tidy, according to the RHS.

The guidance comes from the RHS's four-year Plants for Bugs research project (2015-19), which was designed to test whether the geographical origin of garden plants affects the abundance and diversity of wildlife they support. The latest results are published in the journal Biodiversity and Conservation.

Over the course of the field-experiment, scientists studied 36 garden-border sized plots containing hardy plants native to one of three geographical regions: the UK, the Northern Hemisphere (excluding the UK), and the Southern Hemisphere.

Analysis of the tens of thousands of invertebrates recorded from the leaves and stems suggested that although all the geographical groupings of plants supported large numbers of invertebrates, it was the native plants that were the most successful, supporting 10 per cent more than the next Northern Hemisphere plant group. 

Plants from the Northern Hemisphere supported the second highest abundance of invertebrates, while those from the Southern Hemisphere supported a fifth (20%), fewer invertebrates than native plants. 

Researchers found that regardless of the origin of the plants, the more densely they are planted, or allowed to grow, the greater the abundance of invertebrates of all kinds they supported.

Examples of attractive UK native plants that gardeners can add to their borders include foxgloves, purple loosestrife, common honeysuckle and heather.

RHS principal entomologist Dr Andrew Salisbury said: "The presence of a wide range of invertebrates, such as ladybirds, springtails, spiders and even caterpillars are indicators of a diverse and well-functioning garden eco-system, and so should be encouraged and supported.

"As in all terrestrial ecosystems, plants are the basis of a garden’s food chain. Some insects and other invertebrates feed on leaves and stems, either in their green state (e.g. caterpillars and aphids), or as they decay (e.g. woodlice and springtails) and play host to algae and fungi. These are then prey for other species, such as spiders and parasitic wasps.

"While some of these animals, particularly herbivores, are traditionally regarded as pests by gardeners, they are vital to support healthy populations of natural predators which in turn help keep pest populations under control. And they provide food for garden birds and mammals such as hedgehogs. In short, an abundance of bugs of all types equates to healthy garden ecology.

"In order to help create a positive environment for these valuable invertebrates to thrive gardeners should plant plenty of plants from the UK and relax; refrain from spraying plants at the first sign of pest attack, and reduce trimming and allow some plant debris to accumulate in order to support the garden’s food chain.

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