Native and non-native plants for ground-active invertebrates

To better our understanding of how to garden for wildlife, the RHS led research into whether native or non-native plants best support invertebrates. Here we look at the findings on planting for a range of invertebrates active at ground level.

Quick facts

Five steps to planting for invertebrates active at ground level:

  1. Include plenty of British native plants for herbivores
  2. Grow some evergreen plants for winter cover
  3. Plant densely while leaving a few bare patches here and there
  4. Decide whether planting for pollinators is equally important for you
  5. Plant a wide variety of plants in your garden

An abundance of pollinators and invertebrates of all types equates to healthy garden ecology

Introduction

What are native and non-native plants?

Gardeners in the UK often use a combination of plants from around the world. Some plants grown by gardeners are classed as native, meaning they occur naturally in Britain (i.e. have not been introduced by humans). Other garden plants originate from regions outside Britain, perhaps only from elsewhere in Europe or similar temperate regions of Asia or North America. Or they may originate from southerly regions such as South Africa or Australia where the climate and habitat may be very different from that in Britain. We have such a rich choice of plants in UK horticulture, thanks in no small part to the legacy of plant hunters who brought back many new and interesting plants from their travels.

When talking about plant origins we have divided them into three categories - one native and two non-native;

  • British (native)
  • Northern hemisphere excluding Britain (non-native – Northern, also here termed 'near-native')
  • Southern hemisphere (non-native – Southern, also here termed ‘exotics’)

What invertebrates are found in the undergrowth?

Down at the base of plants in our garden beds and borders there is a bustle of creatures of many sorts. Some may be feeding on dead leaves and stems, algae or fungi. Others are on the prowl for their next meal. And some are simply in transit, passing from one part of the garden to another. These invertebrates are incredibly varied but can be divided into one of four primary functional groups based on what they eat;

Herbivores

Examples: caterpillars and plant-feeding beetles (chewing mouthparts), thrips, aphids and other true bugs (sucking mouthparts)
Food chain function: eat living plants. The group contains generalists which are able to feed on a wide range of plants and some very specialist feeders which only feed on a few plant species. They sometimes damage garden plants

Predators

Examples: predatory beetles (e.g. rove beetles and devil’s coach horse), some true bugs, spiders and parasitoid wasps
Food chain function: eat other animals. They are vital in any healthy ecosystem and help keep some problematic invertebrates in check, including many herbivores

Omnivores

Examples: native cockroach (which are never pests indoors) and some ground beetles (such as the black clock)
Food chain function: eat both plants and animals, feeding on other invertebrates such as vine weevil larvae as well as seeds and other plant material. This broad feeding strategy makes them very adaptable if one food source becomes scarce

Detritivores

Examples: springtails, millipedes, woodlice and some beetles that feed exclusively on dead material
Food chain function: eat decomposing organic matter, of animal or plant origin. They are vital in recycling dead material in the garden. Many also feed on fungal and algal growths

Why are these invertebrates important?

While some of these animals are traditionally regarded as pests by gardeners, they support populations of natural predators, which in turn help maintain a balance of invertebrates in general. They break down dead plant material and recycle nutrients. They also provide food for garden birds and mammals such as hedgehogs. In short, an abundance of invertebrates of all types equates to a healthy garden ecology.

Does a plant's origin affect how well it supports these invertebrates?

In the context of garden plants, it would appear plant origin does have a bearing. However, other factors such as vegetation density and whether a plant is deciduous or evergreen also play an important role. Below are the findings and recommendations to gardeners from recent research.

Key messages for gardeners on planting for invertebrates living at ground level

  1. Overall, the denser the vegetation, the higher the ground-active invertebrate abundance regardless of plant origin. A notable exception is ground-active spiders, which were found in greater numbers among sparser plantings.
  2. The best strategy for gardeners wanting to support ground-active invertebrates in gardens is to densely plant with more native and near-native plants than exotic plants.
  3. Planting schemes based on exotic plants may support relatively more ground-active invertebrates in winter than British native or near-native planting schemes. This is possibly related to the higher proportion of evergreens available in hardy exotic plantings.
  4. Planting schemes based on native plants may support a greater abundance of ground-active herbivores than other planting schemes, but ground-active detritivores show no preference for plant origin.
  5. Species diversity appears to be reflected by invertebrate abundance: as invertebrate abundance increases so does the diversity of species

How to apply this in the garden

Enhance your garden for invertebrates living in the greenery through plant choice:

  • The perfect cover – let planting fill out, but keep some areas sparser to help specific groups, notably spiders. Although not covered in this research, some ground-nesting bees also make use of patches of bare ground.
  • More local – plant densely with plenty of native and near-native plants to support the greatest number of ground-active invertebrates, but be prepared for more nibbled plants than with exotic plant schemes.
  • Winter protection – whatever the plant origin, try to include some evergreens in your garden to give shelter for invertebrates.
  • Decide priorities – choosing more exotics (especially flowering ones) in your planting scheme might mean it supports marginally fewer plant-dwelling and ground-active herbivores, but will mean potentially fewer nibbled plants and should help extend the season for pollinators.
  • Be bio-diverse – for rich species diversity, follow all previous Plants for Bugs recommendations for gardeners. And don’t limit yourself to just a few different plants – this and other studies suggest the greater the variety of plants in a garden, the richer the diversity of invertebrates it will support.

What should I plant?

Our research is not prescriptive on exactly which plants you should plant in your garden but here are a few pointers to help you put into practise the principles described above.

So, if your garden lacks British native plants or you’re not sure what these are, these pages will help;

If your garden has very few evergreen plants and you’d like to add more, try growing evergreen perennials such as Bergenia, Epimedium and hellebore. Or be inspired with our evergreen shrub selections;

Or maybe you’d particularly like to focus your planting on encouraging one group of invertebrates – the pollinating insects (e.g. bees and hoverflies) – in which case our research suggests exotic plants such as fuchsia, hebe and single-flowered dahlias will help to extend the season with pollen and nectar-rich flowers. Here’s more on planting for pollinators;

And remember, the good news is that any planting is better than none, and garden plants originating from all regions in our experiment supported a good number of invertebrates.

Research and further reading

RHS Plants for Bugs research

Plants for Bugs was a four-year study into wildlife gardening, which was undertaken at RHS Garden Wisley in Surrey, and supported by the Wildlife Gardening Forum. Read here for more about the design of the experiment and plants used in the study. The first scientific paper reported on pollinating insects visiting the flowers and the second scientific paper reported on invertebrates living on the leaves and stems.

Recording invertebrates living at ground level

Results from the third scientific paper focused on invertebrates living at ground level among the plants (termed 'soil-surface-active invertebrates'). In total nearly 20,000 individual invertebrate specimens were collected from the plots using pitfall traps (a plastic cup plunged into the centre of each plot and part filled with a 50/50 mixture of water and antifreeze). Each plot was set with the trap for a two-week period on five or six occasions each of the four years the experiment ran. The catch was then sorted and identified in the laboratory.

Further reading


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