Send for a very big dock leaf: Giant stinging nettles are growing to 11ft

Stinging nettles, which used to threaten only ramblers in shorts and skirts, have put on a frightening growth spurt and now threaten even the best-protected of walkers.

Stinging nettles, which used to threaten only ramblers in shorts and skirts, have put on a frightening growth spurt and now threaten even the best-protected of walkers.

Urtica dioica is flourishing so successfully that the plants are growing well beyond their text-book maximum height of just under 5ft. In some Wiltshire river valleys, for example, nettles have been found to be giants more than 11 feet tall.

And anyone who thinks they can escape their stings by avoiding the West Country will be unlucky, because the plants are spreading. They are one of a number of plants now crowding out many less robust wild flowers and causing major changes in the nature of this country's vegetation.

The wild-flower conservation charity Plantlife believes the reason for the change is an increase in Britain's soil fertility caused by years of chemical enrichment of the land by the nitrogen-based fertilisers used in intensive farming, and by nitrogen deposits from road traffic pollution.

Besides nettles, other plants doing extraordinarily well include cow parsley, which now fills almost every roadside verge to overflowing with its white feathery flowers in May, as well as hogweed, cleavers and goose-grass and a number of coarse grasses.

Their luxuriant growth is the terrestrial equivalent of the algal blooms that have been seen in recent years on lakes and in the sea, and which are also caused by an excess of nutrients such as nitrates and phosphates.

Another consequence of this change in soil nutrients, Plantlife said in a new report, is that many other common plant species, which require poor soils in which to flourish, are now in decline in many parts of the country.

In its study, "Where Have All the Flowers Gone?", the charity says that common wild flowers are becoming more scarce in every county, and many of the rarer varieties are dying out completely.