Cool spring weather perfect for planting onions

Q. How do I grow onions?

A. Onions are a cool season plant so they can be planted in the spring when the soil is 35 degrees or warmer and not wet. You can buy onion sets, which are year-old small onions, for both green (scallions) and dry onions to plant in your home garden. Larger sets produce scallions; small to medium sets produce dry onions. You can also buy transplants. In Illinois, the best types of onions to grow are day-neutral or long-day types. Sets and transplants are available at nurseries or by seed catalog.

Choose well-drained, organic matter-amended soil in a sunny (at least half a day) location to plant the onions. If you do not have well-drained soil, you can use raised beds or containers instead.

Sets

Each small dry onion set will produce one onion, so you want to plant them 3 to 4 inches apart in a furrow that is 1 to 2 inches deep. For the larger scallion sets you will want to plant the sets 1 inch apart at 3 to 4 inches deep, also in a furrow. Allow a foot or more between rows in a bed. Plant the sets with the pointed end up. Cover them with soil.

Transplants

Transplants are good for growing large dry onions for slicing. Space plants 4 to 5 inches apart at a depth of 1 to 1½ inches. Allow rows to be a foot or more apart in a bed. Apply a one-half cup of starter fertilizer to each plant.

Care

Onions are shallow-rooted, so they need constant moisture, but take care not to leave them sitting in water as that could encourage disease. Keep moisture even by mulching with straw. Lightly till or hand-pull weeds as they will compete with the onions for water and nutrients. Fertilize evenly as too much nitrogen can cause dry onions to develop large necks. If this happens, harvest the onions with large necks as soon as you can. If an onion begins to flower, use it as a scallion as soon as possible.

Harvest

Scallions can be harvested any time the base of the plant is greater than one-half inch in diameter. Dry onions are ready to harvest in July or August when the tops have fallen over naturally. The dry onions need to dry out with good air circulation after being harvested so they cure fully. You can lay them out on clean screens or slats that are in a dry, well-ventilated area of your yard. Store them in a cool, dry, well-ventilated area until you are ready to enjoy them.

- Nancy Degnan

• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines, and University of Illinois Extension, North Cook Branch Office, Arlington Heights. Call (847) 298-3502 Monday, Wednesday and Saturday or (847) 201-4176, ext. 14, on Fridays.