|'Walla Walla' is perhaps the most popular sweet onion, generally ready for harvest 125 days after sowing. These onions are large, and do well sown in the fall. Nice mild, sweet flavor. Some people eat them like apples.
Onions are a hardy biennial grown as annuals. Leaves and flower stalks are hollow and bases swell to form a bulb. Bulbs may vary in color from white, to yellow, or red. All onions can be eaten as green onions, but spring, bunching and scallions are grown specifically for their tops.
Onions are day length sensitive. American and Spanish onions require long days for bulb production and the Bermuda onion short days. Cool weather is needed for top production and warm weather for bulb production. Onions are frost hardy and can be planted 4 weeks prior to your last average frost date. Southerners can plant onions in the fall or winter.
When preparing soil, dig in 1 pound of complete fertilizer per 100 square feet. Onions do best in fertile, deep, well-drained soil. Onions are available as seed, sets, or transplants. Sets are onions that stopped growing when very small. If selecting sets, choose ones with bulbs smaller than your pinky finger nail. Transplants offer more selection and usually are more reliable about producing bulbs. Seeds offer the greatest variety and are least expensive, but often are more disease prone and take quite a while to get going.
Plant transplants or sets 1 to 2 inches deep and about 3 inches apart in rows about 12 to 18 inches apart. Seeds should be planted at a depth of 1/4 inch and thinned to 2 inches apart. Fertilize again about midseason and keep watered until bulbs start to mature. You can recognize this because foliage will start to brown and wither. Keep soil as dry as possible then.