The rule probably applies only during the summer, when there is more natural light to develop blooms, according to trials on pot chrysanthemums. In the long dark winter months, only flowers bought when they are already blooming will prosper.
A campaign aimed at helping people to 'get the best out of their chrysanthemums' has been launched by the trade in advance of the Christmas market. Thousands of posters with details of the findings are being distributed to florists, supermarkets and wholesalers by the Horticultural Development Council.
The research, conducted by Horticulture Research International, followed worries that too many immature pot plants were being marketed, resulting in premature withering, early droop and widespread customer discontent. According to HRI, this was because flowers were being plucked too early from the overwhelming artificial radiance of winter glasshouses into domestic twilight.
Natural winter light in a house is about one-fifth the strength of summer light and only one-tenth or less of that generated by the high-pressure sodium lighting of glasshouses.
Dr Ruth Finlay, of HRI, said: 'A plant sold to the trade in summer with most of its blooms in bud or just emerging may well go on to produce an attractive display, but if plants are marketed prematurely during winter , tight buds are likely to die.'
Between 8 and 10 million pot chrysanthemums, known in the trade as 'potmums' and worth about pounds 20m, are sold each year.
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