How to Grow Ailsa Craig Onion
Allium cepa
Ailsa Craig Onion is a celebrated heirloom variety of Allium cepa prized for its robust flavor and reliable yield. Gardeners grow this cool-season crop to enjoy fresh bulbs in salads or cooked dishes, benefiting from its moderate resistance to common ailments.
📷 Wikimedia CommonsStarting Ailsa Craig Onion: indoors or direct sow?
🌾 Sow directly in the garden — Ailsa Craig Onion is not usually started indoors.
While you can start seeds indoors for an early head start, direct sowing outdoors 2 to 6 weeks before the last frost is often preferred for onions.
Soil, care & harvest
Prepare loose soil with a pH between 6.0 and 7.0 for optimal growth. As a cool-season crop, sow seeds indoors 4 to 6 weeks before the last spring frost or direct-sow outdoors during this window. Press seeds lightly into the soil at a depth of roughly an inch. Expect germination in 10 to 15 days once conditions are right.
Space plants 4 to 6 inches apart with rows set 12 to 18 inches wide. These onions do not require support or trellising. Provide 1 to 1.5 inches of water weekly, reducing frequency as bulbs mature. Apply a light mulch to retain moisture and suppress weeds, but avoid piling soil against the necks.
Watch for onion thrips, maggot larvae, and cutworms; practice crop rotation and inspect regularly for early detection. Prevent downy mildew, purple blotch, and white rot by ensuring good air circulation and avoiding overhead watering. Harvest after approximately 110 days when tops fall over, then cure bulbs in a dry, airy spot.
When to Plant Ailsa Craig Onion
Planting windows vary by USDA hardiness zone. Look up yours by ZIP code.
| Zone | Start Indoors | Direct Sow | Harvest |
|---|---|---|---|
| Zone 1 | — | June – July | September |
| Zone 2 | — | May – July | September |
| Zone 3 | — | May – June | August – October |
| Zone 4 | — | April – June | August – October |
| Zone 5 | — | April – May | August – November |
| Zone 6 | — | April – May | July – November |
| Zone 7 | — | March – May | July – November |
| Zone 8 | — | March – April | June – December |
| Zone 9 | — | February – March | May – December |
| Zone 10 | — | January – March | May – December |
| Zone 11 | — | January – February | April – December |
| Zone 12 | — | January – February | April – December |
| Zone 13 | — | January – February | April – December |
Companion Plants for Ailsa Craig Onion
✓ Good companions
Onions repel cabbage worms, flea beetles, and other brassica pests
Onions repel carrot flies while carrots help break up soil for onion bulb development
Shallow-rooted lettuce doesn't compete with onions and benefits from onion's pest-repelling properti…
Both repel similar pests and marigolds add extra nematode control
Attracts beneficial insects and doesn't compete for space or nutrients
Onions deter aphids and other soft-bodied insects that attack pepper plants
Onions repel slugs and other pests while improving strawberry flavor
Onions deter tomato hornworms and aphids, while tomatoes don't compete for nutrients
✗ Keep away from
Both compete for similar soil nutrients and can inhibit each other's growth
Onions can inhibit bean growth and nitrogen fixation by rhizobia bacteria
Onions stunt pea growth and interfere with their nitrogen-fixing capabilities
Nutrition Facts
Per 100g serving (USDA FoodData Central)
