Depending on the variety, bulb onions grown from transplants or sets will need about 3 months to reach maturity. Many onions are ready to pull up and harvest by late summer, roughly late July or early August.
In the Northern states onion bulbs are generally allowed to become as ripe as possible before harvest. Professional growers usually prefer that the tops ripen down and shrivel and that the outer skin of the bulbs be dry before the onions are removed from the soil. In the Southern states, where the onions are not cured so thoroughly, they are often pulled about the times that the tops begin to break and fall.
On farms, the ripening process may often be hastened by rolling a very light roller or barrel over the tops to break them down. This process is frequently spoken of as “barreling.”
Where the bulbs are practically on the surface they may be pulled by hand and thrown in windrows consisting of eight to ten onion rows.
In any case it will be necessary to gather onions from the soil by hand. After lying in the windrows for several days and being moved around occasionally you can remove the tops by twisting them off or by using ordinary garden shears.
If the onion bulbs are considerably covered with soil it will be necessary to employ a cultivator for lifting them up from the soil. As the tops are removed the bulbs are generally placed in wooden crates or other containers for drying. You can learn about the best tools for harvesting onions and other vegetables.
Harvesting onions in the early morning is recommended. If the sun happens to be bright and hot on the day of harvest, try moving the onions to a shady part of your yard. Note that the stronger and hotter the sun, the greater chance there is of sunburn on the bulbs.
Many gardeners let the bulbs air dry in the same spot that they were harvested for a day after an early morning harvest. Itâ€™s best to let your onion bulbs dry out thoroughly before storing them. Do not expose the onions to morning dews.
Please note that too much exposure to the sun may injure the onion bulbs, so eventually youâ€™ll need to store them in a safe place. In some cases, a certain color is desirable for the onions, as is the case with the fancy White Globe onion, and these could be discolored or damaged by prolonged exposure to sun and rain. Therefore, it is necessary to cure them indoors to maximize their shape and color.
Another way to harvest is to start the curing process by partially removing the onions from the ground, leaving part of the bulb exposed. The onions will begin to dry out and cure while still in place. You should cure your onions at least two weeks and in some cases it is recommendable to cure them a full month.
You can then chop off the top of the onion with a sharp, clean knife or a pair of pruners. Leave just a little of the top part of the onion intact. As you cut the tops of the onions for storage, check from damage such as cuts and bruises on the main bulb. Also check for evidence of disease.
If the onions are stored too close together, there is the potential for disease to spread from one onion to the next. Please see our troubleshooting guide to learn more about common diseases that affect onions and how to treat them.
Bolting occurs when your onions send up flower stalks. If you see flower stalks emerging from your onions, harvest them immediately. Unfortunately, onion bulbs will not grow any larger once they bolt. Another problem is that the flower stalk comes from the center of the onion bulb. Therefore, you should eat these onions quickly as they do not store well after bolting.