If you go down to the garden centre today...

...you may be in for a big surprise. A major new study shows plants and shrubs are flowering up to four weeks ahead of their seasonal schedules

Some common flowers are blooming so early these days that there is a danger that garden centre plant labels have become meaningless, a new survey has revealed.

Some common flowers are blooming so early these days that there is a danger that garden centre plant labels have become meaningless, a new survey has revealed.

The study, by the Royal Botanic Garden, Edinburgh, shows that certain plants and shrubs, such as spurge laurel and winter jasmine, have advanced their flowering time with the warming climate so much that they have actually shifted seasons. Others, including Anemone blanda, Lonicera korolkowii (a honeysuckle), and Prunus cerasifera (an ornamental plum), have been flowering progressively earlier in recent years and are now blooming about a month earlier than just three years ago.

With the nation expected to besiege garden centres this Easter weekend for the first big plant-buying spree of the year, the study shows that many descriptive labels on flowers have already, in the words of one expert, "lost their meaning". And, if this trend continues, says another, people will have to change how they plan their gardens.

Hazel is perhaps the most extreme example of early blooming. The first flowering of one tree in Edinburgh has advanced by 56 days in three years - from 21 January 2002 to 26 November 2004. Botanist Dr Geoffrey Harper said: "If the trend continues, this spring-flowering shrub will become an autumn-flowering one."

Other star performers were a range of plants that have flowered earlier each year since 2002: winter aconite (flowering 2 February in 2002, 7 January this year); spring snowflake, now two weeks ahead of 2002; dog's tooth violet, 11 days earlier than 2002; and candytuft and crab apple, three weeks ahead of 2002. Last year, snakeshead frittilary, not due out at the time of 2005's survey, was three weeks ahead of 2002.

Some plants are quite erratic in their flowering, like spring vetch which opened in mid-February in 2002, then mid-January last year, and early March this year. A few others are actually later, such as arabis, which has become more shy over recent years and is now a fortnight later than in 2002, and a variety of lesser celandine called "Brazen Hussy" which, despite its name, is actually less forward these days than it once was.

All this information comes from Edinburgh's records of phenology (the study of the timing of natural events). These date back to 1850, with lengthy gaps, but, in 2002, experts at the gardens started systematically recording first flowering dates for 65 species. They have now drawn up an Edinburgh Spring Index using the date of first blooms of plants that flowered before 15 March and for which there are complete records. The index shows that the 21 plants that fit these criteria flowered this year, on average, 20.4 days earlier than in 2002.

Dr Stephan Helfer, who studies weather as well as plants at Edinburgh, says the trend for 30 years has been warmer winters, with summer showing a small cooling. He said soil temperature is crucial to triggering flowering, especially in bulbs, and that, helpfully for early bloomers, 2002, 2003 and 2004 all had warmer than average autumns.