Plant imports at Chelsea have hit the headlines again, but how important is it to buy British?

Green politics

Politicians have singled out the 100% New Zealand garden, criticising the environmental cost of shipping about 1000 plants – some rare or endangered - halfway across the world just for a few days. The garden's designer, Xanthe White points out that the plants will remain in Britain, in RHS Wisley's new glasshouse. And, she argues, there's a conservation message behind the garden.

The same reasons led another exhibitor, Borneo Exotics, to ship 47 boxes of rare pitcher plants from Sri Lanka for Chelsea."We believe in conservation by cultivation," says Rob Cantley. "We're bringing it to people's attention that these plants exist. If they don't get recognition, they don't get protection."

Plants don't have to be rare to travel long distances. Imports now account for about a quarter of all plant sales in the UK. The growing international trade is worrying experts – but carbon emissions aren't their main concern.

The list of diseases, pests and invasive weeds brought into the UK on imported plants is long and depressing. In recent years, New Zealand flatworm and sudden oak death arrived as stowaways.

“There's a trend towards globalisation in the nursery trade at the moment which is potentially a serious threat." says Guy Barter, head of the RHS advisory service. "Plants are living organisms, and they carry associated organisms with them.”

Strict regulations governing imports require plant passports and quarantine. The 100% New Zealand garden has itself spent the last month in isolation. Guy Barter believes keeping these regulations tight is our main weapon.

"The scientific view about the risk is all very well from a purist point of view, but the world doesn't work like that," he says. "The only realistic way forward is to ensure that regulations are enforced."

The RHS advises gardeners to buy British-grown plants wherever possible, but professionals in the nursery trade are quick to point out that plants have been arriving from abroad since the first plant hunters set off in search of roses and rhododendrons.

"There's nothing mysterious about plant imports and no hidden threat going on," says Erica Harper of the Horticultural Trades Association. "We shouldn't have an island mentality about this – our gardens are much richer as a result of plant importing."