A hardy crop grown globally, onions are a staple in vegetable gardening. They can be grown for their mature bulbs, or simply for their green tops. Rich in dietary fiber, vitamin C, potassium, iron, and organosulfur compounds, onions have been linked to cancer prevention and lowering blood pressure and cholesterol.
Onions are a hardy crop adapted to a wide range of growing conditions. Day length is important in variety selection of bulbing onions. Growers north of 38 degrees latitude should plant long day varieties as early as possible to achieve full size prior to maturity. Growers south of 38 degrees should plant short day or intermediate day varieties as these need less day length to reach full size. Green/bunching onions can be grown at any latitude. Onions grow best in fertile, well drained soils with a pH of 6–6.8.
grow calendar tool to find specific dates for your region! Seeds germinate in 10-14 days.
Plant indoors in starter pots or trays ~7-9 weeks before the desired transplant date. Transition outside (harden) for 7-14 days before outdoor transplant. Space 3-5" apart for full-sized bulbs, or 1-2" for bunching types.
Keep consistently watered and well weeded. Shallow roots require light, frequent irrigation when plants are young.
Pests and Disease
Botrytis Leaf Blight, Gray Mold, Downy Mildew, and Purple Blotch are fungal diseases of onions that can be challenging to control. Practice 3–4 year crop rotations for all onion family crops (onions, shallots, leeks, garlic) and thoroughly compost or turn under all crop debris. Cover with floating row cover in areas with high onion maggot or thrips pressure.
Onions for use in the green stage are harvested as soon as they attain edible size.
Onions growing to full bulb stage will have their green tops drop down when onions are ready to be harvested. Harvest when tops are between 80–100% broken down. Store in a cool, dry place.