For weeks now, the shops have been filled with half-hardy bedding plants like marigolds, lobelia, tender geraniums, impatiens and verbena. But it's safe to plant them out now only in the milder parts of the country; in the midlands, on high ground and in other chilly and frost-prone parts it's best to wait until the end of the month. When buying summer bedding be very fussy about the quality of plant: choose bushy or plump specimens that are growing in nicely moist soil. And, while you may be happy to buy everything else in a supermarket, be wary of trays of plants prominently displayed to catch the impulse shopper. Close examination will often show that they are not in the best of health.