Scientists believe they are well on their way to debunking one of the most pervasive of all axioms in gardening: that when it comes to plants, “native is best”.
A team of researchers from the Royal Horticultural Society (RHS) has just completed a four-year study into how much wildlife can be supported by native, near-native and exotic plants. It is the first scientific experiment to test a widely accepted hypothesis that plants that originate in Britain are better at sustaining our insect populations.
In a finding that looks set to overturn generations of gardening advice, early indications strongly suggest that all classes of plant are capable of supporting a large and diverse range of invertebrate creatures, according to the project’s assistant manager, Andrew Salisbury.
“This is very exciting. The idea is solidly out there that if you want native insects you should only plant native plants. That’s been the advice for years. Initial analysis shows this is not the case,” said Mr Salisbury, though he cautioned there was much more detailed analysis to be done.
“This is great news for gardeners because it indicates that no matter what you plant it will support a wide range of biodiversity,” he added. “Even if this knowledge doesn’t change what you plant, it will make you feel less guilty about the near-native and exotic plants in your garden.”
The research emerged just days after the EU announced plans to clamp down on harmful non-native plant and animal species such as Japanese Knotweed, which can destroy the foundations of skyscrapers, and Zebra mussels from Russia, which grow prolifically and clog intake pipes at water treatment plants. The EU will draw up a blacklist of invasive alien species in order to limit their spread.
However, only a small minority of the estimated 2,000 alien plant species in the UK are invasive – or fast-spreading – and causing problems for natural habitats or the infrastructure. The RHS research indicates that, overall, non-native plants are a significant force for good.
Native plants are classed as species which arrived in Britain after the last ice age without the assistance of humans. They include holly, ivy, honeysuckle, Foxglove, Majoram, Purple Loosestrife and raspberry.
However, today they account for only about 30 per cent of garden plants, the remainder being non-native species such as sunflowers, Lavender, dahlias, Echinacea and the malus pumila apple, which have entered the country through trade.
“There is still much work to do but I suspect the final conclusion will be that we don’t necessarily need just natives and that we should give careful consideration to natives, near-natives and exotic species,” Mr Salisbury said.
For its so-called Plants for Bugs programme, the RHS has coined the new term of “near-native” plants for species not native to Britain but originating in the Northern hemisphere and arising from similar eco-systems.
The clearest conclusions the RHS has come up with so far relate to pollinators. They are that, while hoverflies prefer native plants, bees are drawn more to near-native species and wasps are most attracted to exotic plants.
Mr Salisbury and his colleagues have recorded the activities of approximately 80,000 invertebrates on plots at the main RHS garden in Wisley, near Woking in Surrey. They will analyse the data over the next two years, starting with pollinators. They will then examine the relationship between various classes of plants and herbivores such as caterpillars and aphids, predators such as spiders and ground beetles and with the whole natural community.
“Ultimately we’ll be producing a guide on the optimum way gardeners can help wildlife by using native and non-native plants in gardens,” said Plants for Bugs project manager Helen Bostock.
Adrian Thomas, gardening expert at the RSPB, said: “This doesn’t mean that every exotic plant is wildlife manna, but choose them well and you can have a garden full of gorgeous flowers from across the globe which delivers a home for nature at the same time.”
But not everybody is convinced. Matt Shardlow, head of the Buglife insect charity, has scrutinised the findings the project. He said: “There are very few relationships that look robust and likely to be scientifically proven.
“Even when recording the visits to flowers by bees, it is nearly impossible to tell if the bee is examining the flower and being disappointed by not finding suitable pollen and nectar or is delighted to find the resource it is seeking.”