Small urban gardens are a haven for insects, even in the presence of invasive plants

A study of small urban gardens in the Netherlands found that they can be havens for insects and other wildlife. The two most effective factors were having a lot of plants and a wide variety of plants, whether or not the plants were native.

“Even in a really small garden, just a few plants can make a big difference.” Joe Morpurgo At Leiden University in the Netherlands.

Morpurgo says there have been some studies on biodiversity in larger gardens, but virtually none on smaller ones, so in 2019 his team surveyed 65 urban gardens in Amsterdam and The Hague, all measuring less than 10 square metres.

The researchers measured factors such as the total number of insects, the number of different species, whether the plants were native, and the area covered by the plants. Plant cover was calculated by adding up the area covered by individual specimens, so the garden’s cover can be greater than the area of the land due to plant overlap.

The researchers found that insect abundance and species richness were strongly correlated with plant cover and plant richness, but surprisingly, neither garden size nor native plant cover made any difference.

In theory, native plants should be better: Pollinating insects often adapt to particular flower shapes, and some plant-eating insects will eat specific varieties.

There are several possible explanations for why the proportion of native plants had no effect, Morpurgo said. For example, insects that breed in cities could be omnivorous, or many of them could be invasive species (the study did not categorize insects as native or not).

A study on the large-scale gardens of Wisley, England produces almost the same results“The more plant matter there is, the more invertebrates there are.” Andrew Salisbury These studies were led by staff from the Royal Horticultural Society (RHS).

But one RHS study found that native plants could support slightly higher numbers of plant-eating species, such as caterpillars, Salisbury said.

Morpurgo said he would continue to encourage people to grow native plants, which he said have many more benefits, including cultural value as well as helping insects.

His main advice is to do nothing and just allow plants, even those we might call weeds, to grow and attract wildlife: “If you leave everything alone, nature will come into your garden,” says Morpurgo.