Weymouth, Mass. — During late April and May this year, all of England was ablaze with colorful flowers - wallflowers (Cheiranthus cheiri) for the most part. Their bold brilliance - yellows, reds, mahoganies, and magentas predominating - did much to brighten the garden scene in an overly wet season.
Breeders have produced from a once-spindly, almost shy plant that would cling to a hedge or a wall for protection a compact dwarf variety that can stand alone.
In the process it has become one of the more popular bedding plants of Europe and is likely to become popular wherever it can grow.
The question then is this: Can it be grown in North America? The answer, apparently, is yes and no.
The Pacific Northwest - Oregon, Washington, and up into British Columbia - and much of coastal California provide the ideal, moderately cool growing conditions wallflowers like best. But all is not lost for would-be wallflower growers in other regions.
The wallflower, a member of the mustard family, does best as a biennial. Seed sown in late spring produces plants that grow almost to maturity during the summer, go into semidormancy during winter, and revive to bloom prolifically the following spring.
Apparently it is not winter's cold (wallflowers withstand temperatures down to zero degrees F., or minus 20 C.) but the hot summers that bother them. They also do not like the strong, drying winds that so dominate March weather in much of the country.
Despite these disadvantages, an increasing number of North American gardeners , particularly those who have visited Britain in the spring, are trying to raise this European favorite. Toni Sorrell, technical adviser in the United States to the British seed company, Thompson & Morgan, makes these suggestions:
* If you live in a suitable West Coast climate, sow seeds now in flats and transplant the young seedlings into a holding bed or into larger flats, where they will do much of their growing.
* In September, or about the time you would begin to consider planting spring bulbs, set out the wallflowers in their permanent bed, about 12 inches apart. Give them some protection if yours is a windy area. When spring arrives, you should get the sort of bold display of floral color that normally is only associated with midsummer.
Increasingly, gardeners in less-hospitable regions are growing wallflowers as well, but they must take a different tack, according to Ms. Sorrell. She suggests sowing the seeds in mid-August in most northern areas of the US, thus allowing the plants to grow when the heat of summer begins to tail off.
Transplant to individual pots and bring them indoors, or into a greenhouse, once frost threatens, so that the plants can continue to grow to full size (12 or more inches tall).
At this stage hold the plants under cool conditions (in a moderately lighted shed or even a cold frame where temperatures will not fall below zero degrees F.) until they can be planted outdoors in the spring. First, however, you must condition them over a week or two to air movement.
In the US, wallflower seeds are available from Thompson & Morgan at PO Box 100, Farmingdale, N.J. 07727.