Onion Growing Guide

Onions are versatile, hardy vegetables that thrive in various climates and are a staple in many culinary dishes. Here’s how to successfully sow and grow onions:

When to Sow

Indoors: Sow onion seeds 8-10 weeks before the last frost date.
Outdoors: In early spring, sow seeds directly as soon as the soil can be worked. In mild climates, sow onions in the fall for a spring harvest. For more tips, check out growing onions from seeds or sets.

Indoor Sowing

Start seeds in seed trays or small pots with a light, well-draining soil mix.
Sow seeds 1/4 inch deep and keep the soil consistently moist.
Place trays in a sunny location or under grow lights. Germination takes 7-14 days.
Transplant seedlings outdoors once they are 4-6 inches tall and the frost danger has passed.

Outdoor Sowing

Choose a sunny location with well-drained soil.
Sow seeds 1/4 inch deep, spacing them 4-6 inches apart in rows 12-18 inches apart.
Water gently after sowing and keep the soil moist until germination. Thin seedlings to 4-6 inches apart as they grow. For raised bed setups, see onions in raised beds.

Care & Maintenance

Light: Onions require full sun.
Watering: Water regularly, keeping the soil evenly moist but not waterlogged.
Mulching: Mulch around the plants to retain moisture and suppress weeds.
Fertilizing: Onions benefit from a side-dressing of compost or balanced fertilizer. For specific recommendations, see best onion fertilizers. Avoid covering the tops of bulbs as they mature.

Pests & Diseases

Pests: Onions can attract onion maggots and thrips. Use row covers to protect young plants.
Diseases: Rotate onion crops each year and ensure good air circulation to reduce the risk of fungal diseases like downy mildew. Avoid overhead watering.

Harvesting

Onions are ready to harvest when the tops yellow and fall over.
Use a garden fork to lift the bulbs from the soil. Cure the bulbs in a warm, dry place with good air circulation for several weeks. Once outer skins are papery, trim the tops and roots. Store in a cool, dry place. For more details on storing, see how to cure and store onions.

Garden Use

Onions are great for companion planting, especially with carrots, lettuce, and tomatoes, as they help deter pests.
They thrive in garden beds, raised beds, or containers and are perfect for crop rotation to maintain soil health. Learn more about onion companion plants to maximize your garden's productivity.

Onion Growing GuideUpdated 11 days ago