Onion - Illinois Vegetable Garden Guide - University of Illinois Extension


onionThe easiest and surest way to grow good onions, either green or dry, is to use sets. Sets are small onions, less than an inch in diameter, that were grown from seed the previous year. Onion plants are sometimes used, especially for growing the mild Sweet Spanish type. Texas varieties of onions, which are normally grown in the south, do not produce satisfactory yields in Illinois.

For green onions, place the sets upright about 1 inch apart in a furrow about 3 to 4 inches deep. For dry onions, place the sets upright about 3 to 4 inches apart in a furrow 1 to 2 inches deep. Cover the sets with soil. The larger sets are preferable for green onions while medium-sized sets are best for dry onions.

For good yields of mature dry onions, plant early in the spring as the soil can be prepared.

Smut, downy mildew, purple blotch, neck rot, and pink root are some of the diseases found in onions. All white onions are susceptible to smudge. Insects that cause the most trouble are thrips and cutworms.

You can harvest green bunching onions 4 to 6 weeks after planting sets. Dry onions will be ready in 3 to 4 months, about late August or early September.

Dry onions are ready to harvest when the necks are thoroughly dry or about 95 percent of the tops have bent over. Pull the onions and place them under cover to dry. Drying will take from 2 to 4 weeks. Then cut off the tops about an inch above the bulb, place the onions in a well-ventilated container, such as a slatted crate or mesh bag, and store in a cool, dry place. The best conditions for storage are a temperature of about 32° F. and a relative humidity of 70 to 75 percent.

Crop Amount for 100
ft of row
Variety recommended for use in Illinois Days to harvest Resistant to
Onions 2-3lb Sets
Ebenezer 90
Golden Globe 90
¼ ounce Seed
Early Yellow Globe 90 Fusarium rot
Yellow Sweet Spanish 110
Walla Walla Sweet 100
Southport Red Globe 110 Fusarium rot
Benny's Red 105
Southport White Globe 110
White Sweet Spanish 110
Vegetable Hardiness Recommended planting period for central Illinois (b) Time to grow from seed to field (c)
For  overall
Onion, from seed Hardy March 25 - April 15 April 1 ...
Onion, from plants or sets Hardy March 25 - May 1 April 1 ...
Vegetable Spacing in row
Seed to sow per foot Distance between plants when thinned or transplanted Distance between rows Planting depth
inches inches inches
Onion, from seed 10-15 2-4 12-18 ½-1
Onion, from plants or sets ….. 1-4 12-18 1-4