How to Grow Onion
Allium cepa
Allium cepa is a versatile cool-season vegetable prized for its pungent flavor in salads and cooking. Gardeners grow these hardy bulbs to add essential nutrients and long-lasting harvests to their spring or fall gardens.
📷 Wikipedia: OnionStarting Onion: indoors or direct sow?
🌾 Sow directly in the garden — Onion is not usually started indoors.
Onions are typically direct-sown outdoors or started indoors and transplanted once seedlings have developed their first true leaves.
Soil, care & harvest
Prepare loose, well-draining soil with a pH between 6.0 and 7.0. As a cool-season crop, sow seeds indoors 8-12 weeks before the last frost date or direct-sow outdoors 2-6 weeks prior to that date. Press seeds gently into the soil at a depth of about half an inch. Expect germination within 7 to 14 days once conditions are right.
Space seedlings 4 to 6 inches apart to ensure proper bulb development without crowding. These plants do not require trellising or support structures. Provide moderate watering, aiming for about one inch per week, and keep the soil consistently moist but not waterlogged. Apply a light layer of mulch around the base to retain moisture and suppress weeds.
Watch for onion maggots, thrips, and rust diseases; practice crop rotation and remove infected leaves immediately to prevent spread. Harvest when tops naturally fall over or after 90-120 days from planting. Gently lift bulbs with a fork, cure them in a dry, airy spot for two weeks, then store in a cool, dark place.
When to Plant Onion
Planting windows vary by USDA hardiness zone. Look up yours by ZIP code.
| Zone | Start Indoors | Direct Sow | Harvest |
|---|---|---|---|
| Zone 1 | — | June – July | December – September |
| Zone 2 | — | May – July | December – September |
| Zone 3 | — | May – June | December – October |
| Zone 4 | — | April – June | November – October |
| Zone 5 | — | April – May | November |
| Zone 6 | — | April – May | November |
| Zone 7 | — | March – May | October – November |
| Zone 8 | — | March – April | October – December |
| Zone 9 | — | February – March | September – December |
| Zone 10 | — | January – March | August – December |
| Zone 11 | — | January – February | July – December |
| Zone 12 | — | January – February | July – December |
| Zone 13 | — | January – February | July – December |
