How to Grow Onions - Part 1
A tip sheet on how to grow and care for onions.
Onion (Allium Cepa)
- Family: Alliaceae (Onion)
- Season: Cool
- Ease of growing: Moderate
- Nutrient needs: Medium
- Water needs: High
- Common propagation: Transplants
- Germination temperatures: 45°F to 85°F
- Germination time: 4 to 20 days
- Viability: 1 to 4 years
- Direct sow: April to early May
- Weeks to grow transplants: 10 to 12
- Start: February to March
- Plant out: April to May
- Typical Spacing: 2” x 18”
- Plants per square foot: 9 to 16
- Time to harvest: 85 to 110 days from transplants
Onions are classified by their:
- Shape - flat, round or globe;
- Color - red, yellow or white;
- Pungency - sweet or pungent, or
- Bulb response to day length - forms bulbs during long, intermediate or short days.
Most of the onions grown in Michigan are the pungent, yellow, globe type. These types prefer Michigan’s cool conditions. Onions grown for their immature green stems are called bunching onions or scallions. You can harvest any onion early and use it as a bunching onion, but not all bunching varieties will produce a large bulb. Avoid using “short day” onions in Michigan.
Preparation and planting
Onions prefer cool weather, but they grow in all regions of the country. Gardeners have a number of ways to start plants. Direct-seeded onions can take four months to mature, so using transplants or sets is generally preferred. Sets are plants (small bulbs) grown the previous season.
Onions require a constant supply of moisture because of their limited root system. Treat them well prior to bulbing; the larger the plant, the larger the bulb. Weeding is extremely important for this slow growing crop. To ensure maximum yields and mild flavor, provide extra water towards the end of bulbing and until the tops fall over. Dry weather after the tops fall over is welcomed because the onions will cure faster and store better.
Insects: Onion maggots and thrips
Diseases: Smut, botrytis leaf blight, downy mildew, Fusarium basal rot, bacterial soft rot
Harvesting and storage
For winter storage, allow onions to grow until the tops fall over naturally. If they need to be harvested sooner, knock them down. Leave the bulbs in the ground one to two weeks to develop thick skins. Harvest after the majority of leaves are dry. Leave 1 to 2 inches of neck on the onion to ensure a tight seal after drying. After digging, spread them outdoors in a sunny, dry place for drying. This should take three to seven days, depending on the weather. When stored indoors, they should be in a shady, warm and dry place.
Developed by James Manning, Undergraduate Research Assistant, and Daniel Brainard, Vegetable Extension Specialist; MSU Department of Horticulture; Gary Heilig, MSU Extension educator.