Just one blip like that even if it runs counter to a well-established trend can mean death for marginal plants

Just one blip like that, even if it runs counter to a well-established trend, can mean death for marginal plants. Self-preservation, not altruism, is at the centre of our concerns about global warming. And Mike Nelhams, head gardener at the famous garden on the island of Tresco, will never forget the destruction caused by the January frosts of 1987, when 80 per cent of his rare plants were killed. On two successive nights in the 1990s, the gardeners at Crathes Castle in Scotland recorded temperatures of minus 22C, which caused the worst damage in living memory to the plants growing in the sheltered walled garden there.

Lord Burghley, Queen Elizabeth I’s chancellor, was at it way back in 1561. “If the prise be not too much,” he wrote to Thomas Windebank in Paris, “I pray you procure for me a Lemon, a Pomegranate and a myrtle tree.” A hundred years later, the diarist Samuel Pepys went off to see oranges growing in Hackney He ate one while the gardener wasn’t looking. That was in 1666, two years before the coldest period ever recorded in England. Then, for 21 years, frosts came in August, and winters lasted for eight months. In the winter of 1683-4, the river Thames was frozen solid from November until April.

That year, the diarist John Evelyn noted that there had been severe damage to “sipris” (cypress) trees. Despite a trend towards global warming, there will still be sudden frosts in this country which will have a devastating effect on tender plants such as trendy tree ferns and bananas. Gardeners in Sussex may be shivering in a climate 13C lower than that in Notting Hill Then there’s the critical question of winter wet. Mediterranean plants die here, not because they are cold (so is France, away from the coast) but because they are wet at the roots They rot, rather than freeze.

All the UKCIP scenarios predict wetter, even if warmer, winters. Only on well-drained soil, such as the gardeners have at the Chelsea Physic Garden, do tender Mediterranean plants have a chance of surviving. Gardeners in this country now have access to about 70,000 different kinds of plants (our native flora numbers a measly 1,500 species), but growing exotics is not a new thing. But the garden is very sheltered, and the tree is tucked away in the warmest place by the glasshouses, on very well-drained, sandy soil. London, though, is a heat island, wrapped in wasted central heating and car fumes, insulated by heat-absorbing tarmac and concrete.