How to Grow Onions

Planting Onions

Onions are a cool season biennial and grow well in full sun and rich, fertile soil that drains well. Start seed indoors 10-12 weeks before last frost date or sow directly in the garden as soon as the soil can be worked (about 4-6 weeks). Lightly cover the seed (¼”), with plant spacing of 3-4″ for medium onions and 4-6″ for larger onions, with rows at least 18″ apart. The best soil temperature for germination is 75-85° with a pH balance of 5.5-6.5. Be sure to practice good weed control and keep them well watered. Allow at least 7-10 days for germination.

Harvesting Onions

Generally, onions can be harvested at anytime of their growth. For full maturity, harvest about a week after the tops have yellowed and begun to fall over. Carefully lift the onion out of the ground with a fork. Best to do this on a sunny day and leave on top of the soil to dry out for a couple days. Remove the tops with a sharp knife and throw away any bulbs that show signs of decay if you are planning on storing them. Cure them by allowing to hang in a well-ventilated place for 3-4 weeks. Cool slowly and store at near freezing temperatures.

Saving Onion Seeds

Suggested isolation distance is ¼ mile. Allow onion to develop the white, flower head, cut the flower and allow to dry. Separate the tiny, black seeds from the head. Use a thin screen to help clean the seed from debris. Seed will keep for 1-2 years if kept cool and dry.

Common Problems

  • Onions Fly Maggot
    Looks like house fly with slender body and long legs, ¼” long, pointed on one end and blunt on the other. To control, spray with parasitic nematodes which is a popular alternative to insecticides.

Suggested Companions

  • All members of the Cabbage Family
  • Beets
  • Strawberries
  • Tomatoes
  • Lettuce
  • Summer Savory

Poor Companions

  • Peas
  • Beans


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