Onion: Sow and Grow GuideUpdated 14 days ago

Onions are versatile, hardy vegetables that can be grown in various climates and used in countless culinary dishes. Here's a concise guide to successfully sowing and growing onions.

When to Sow

Onion seeds can be sown indoors 8-10 weeks before the last frost date, or directly outdoors as soon as the soil can be worked in early spring. In mild climates, onions can also be sown in the fall for a spring harvest.

Indoor Sowing

Start onion seeds indoors in seed trays or small pots filled with a light, well-draining soil mix. Sow seeds 1/4 inch deep, lightly covering them with soil. Keep the soil consistently moist and place the trays in a sunny location or under grow lights. Onions typically germinate within 7-14 days. Transplant seedlings outdoors once they are 4-6 inches tall and the danger of frost has passed.

Outdoor Sowing

For direct sowing, choose a sunny location with well-drained soil. Sow seeds 1/4 inch deep, spacing them 4-6 inches apart in rows spaced 12-18 inches apart. Water gently after sowing and keep the soil consistently moist until germination. Thin seedlings to 4-6 inches apart once they reach a few inches tall to allow space for bulb development.

Care and Maintenance

Onions require full sun and regular watering, especially during dry periods. Keep the soil evenly moist but not waterlogged. Mulch around the plants to retain moisture and suppress weeds. As onions grow, they may benefit from a side-dressing of compost or a balanced fertilizer. Avoid covering the tops of the bulbs with soil as they begin to mature.

Pests and Diseases

Onions are generally resistant to pests, but they can attract onion maggots and thrips. Use row covers to protect young plants, and consider rotating onion crops each year to prevent disease buildup. Ensure good air circulation and avoid overhead watering to reduce the risk of fungal diseases such as downy mildew.

Harvesting

Onions are ready to harvest when the tops begin to yellow and fall over. Carefully lift the bulbs from the soil with a garden fork and allow them to cure in a warm, dry place with good air circulation for several weeks. Once the outer skins are papery, trim the tops and roots, and store the onions in a cool, dry place.

Garden Use

Onions are excellent for companion planting, particularly with carrots, lettuce, and tomatoes, as they can help deter pests. They can be grown in traditional garden beds, raised beds, or containers. Onions also work well as part of a crop rotation plan to maintain soil health.

For further details, visit the full guide on the Botanical Interests Blog.