Onions will let you know they are finished growing when their necks soften and topple over; this is a natural occurrence and it’s a myth that they need our help doing this. Some gardeners think that knocking the tops over prematurely will encourage larger bulbs but actually it’s the tops that manufacture the sugars and energy that cause the bulbs to enlarge and when the necks are broken prematurely that process slows to a halt. As I learned from long-time farmer’s market gardener June Russell, of Midland, Texas, “onions have the sense to lay over on their own”.
Onions also bulb in response to day length and in Central Texas where I live the short day onion varieties that we plant in the winter begin bulb formation in springtime as the day length reaches 11-12 hours. In the northern half of the state gardeners grow intermediate day onions which require 12-14 hours of daylight and in colder parts of the country where onions mature during the longer days of summer gardeners grow long day onion varieties that require at least 14 hours of daylight. If you have onions that don’t bulb properly then chances are pretty good that you are growing the wrong type of onions for your region.
My short day onions are usually ready to harvest in late May or early June. Once the necks start to fall over it’s a good idea to cut back on water for a few days and let the soil dry out before harvesting. After the soil has dried out for a few days hold onto the stem of each onion and coax them gently from the soil then spread them out in a dry, shady spot to cure for at least 5-7 days. Go ahead and harvest any onions that send up a flower stalk – they are perfectly edible but they will not store very well so eat them first. Prepare dry onions for storage by trimming the roots and cutting off the dried leaves then drop them, one at a time, into a mesh bag or a length of nylon pantyhose. Tie a knot or a twist tie between each onion, then when you need an onion for cooking just snip off the lowest onion just below the knot, leaving the others for later. I hang my onions on a hook inside the pantry so they are always at the ready. They can also be stored in a flat box or crate in a cool, dry place with good air circulation (in other words do not store them in a closed bin or box). An alternative method that works especially well with smaller onions is to leave the tops intact and braid them together. Short day onions do not store as long as long day varieties, but if properly cured they will last about 3 months.
The organosulfides that give onions their pungent taste and smell also have powerful cancer-fighting properties. Since heat can destroy these compounds raw onion will have the highest concentration, but eating lots of raw onions can be hard on those with sensitive digestive systems so a quick sauté is the next best thing. It will lessen the pungency of the onions while retaining most of the organosulfide compounds.