Plant origin and insect diversity

During this most bizarre and worrying month, with events of global concern and impact, this post is serving to highlight the good work of the RHS.

It recently completed a four year study into the effect of native, near-native (northern hemisphere) and exotic plants on invertebrate populations. There are different opinions on how the geographic origin of a plant effects insects. Some favour a strict native planting palette, others are less ecologically didactic permitting exotics like Dahlias or Begonias.

The headline:

"the best way to support invertebrates in gardens and promote a healthy ecosystem, is to choose plantings biased towards British native plants and encourage dense vegetation, while leaving some patches of bare soil."

The study was divided into three: pollinating insects, plant-dwelling invertebrates, ground-active invertebrates. Below are the most important findings from each study:

Pollinating insects, e.g. bumblebees, hoverflies and butterflies

• plant a mix of flowering plants from different countries and regions

• the emphasis should be on native and near-native plants but use exotic plants to extend the flowering season

• regardless of plant origin the more flowers a garden can offer the greater number of pollinators it will attract and support

Plant-dwelling invertebrates, e.g. ladybirds, spiders and earwigs

• the denser the planting, the higher the number of invertebrates that can be supported

• native planting schemes support higher numbers but exotic mixes will extend the feeding opportunities for pollinators

Ground-active invertebrates, e.g. millipedes, woodlice and springtails

• the denser the vegetation, the higher the abundance of ground-active invertebrates, regardless of plant origin

• as abundance of insects increases, so does species diversity

• choose plants biased towards British and near-native planting and add exotics to provide winter evergreen cover