The onions started from seed last October have all gone to flower which is the hazard all those who would cultivate onions must endure. It is often advised that the flower stalk be removed but this serves little purpose for once flowering is initiated there is nothing the gardener can do to promote the formation of the bulb. They can, however, be harvested for scallions and these small bulbs are often sweet enough to be used in salads. Pull them as they are required in the kitchen for they do not last long in storage and you should complete the harvest before the flower stem thickens as it will harden the center of the bulb as it matures.
There are several factors that lead to premature flowering in onions. If you are growing your onions from sets, purchased in the spring, the smaller sets are not nearly as likely to flower as are the larger so for onion sets, smaller is better. We grow our onions from seed sown near the first of October. Our goal is to produce transplants that are large enough to withstand the rigors of winter but not so large that they will flower in the spring. Transplants that are about the size of a pencil by the time they are transplanted in March are ideal.
Even then, a successful onion harvest is not guaranteed. This season we had an unusually warm spell in early April followed by an equally unusual cold spell which likely triggered flowering. We will now have to rely on the spring seeded onions for bulbs and enjoy the fall sown onions as an unanticipated bounty of scallions.
For a further investigation of the Allium genus we invite you to examine Vegetable Gardening the Colonial Williamsburg way, 18th century methods for today’s organic gardeners (Rodale Press)