Light requirements: Full sun.
Planting: Space 6 inches apart.
Soil requirements: All onions need well-drained, nutrient-rich soil. Work at least 3 inches of compost or other organic matter into soil prior to planting. Soil pH should be 6.0 to 6.8.
Water requirements: Keep soil consistently moist until bulbs enlarge. Onion roots are shallow; apply a light layer of mulch to slow water evaporation from the soil. Once the tops of the bulbs push through the surface, remove mulch to allow them to bask in the sun.
Frost-fighting plan: Onions tolerate even hard frosts (temperatures below 28º F). Still, protect newly planted seedlings from late spring frosts by covering plants with straw or a frost blanket.
Common issues: Onion thrips, aphids, and onion root maggots can cause problems.
Harvesting: Pull onions at any stage for fresh eating. Harvest young onions to eat as scallions. For full-sized bulbs, don’t pull onions until bulbs are big and tops start to yellow and fall over.
To harvest, pull onions and shake off soil. Before snipping roots or trimming tops, cure them in a warm, airy place. During curing, roots shrivel and necks dry and tighten. After 7 to 10 days of curing, clip onion tops and roots; rub dry dirt from bulbs, taking care not to remove papery outer skins.
Storage: Store cured, dried, full-size bulb onions in a cool place. Very sweet, juicy onions store best in the refrigerator. Use mild onions within a few weeks of harvest; pungent onions can store for 10 to 12 months.
For more information, visit the Onions page in our How to Grow section.
- Calories: 30
- Carbohydrates: 7g
- Dietary fiber: 1.5g
- Sugars: 3.5g
- Protein: 1g
- Vitamin C: 10% DV
- Vitamin B6: 5%
- Folate: 4%
- Manganese: 5%
- Potassium: 3.5%
The health benefits of onions are so numerous that it is impossible to list them all. Much of this benefit comes from powerful sulfur compounds, the same ones that account for the onion’s eye-watering odor. These compounds, along with chromium, a trace mineral in good supply in onions, and vitamin B6 have been found for help regulate blood sugar, lower total cholesterol and triglyceride levels, and lower blood pressure. Onions have also been found to boost intestinal and bone health and ward off several types of cancer. Researchers say that the more pungent the onion, the greater the load of beneficial phytonutrients.