How to Grow Ailsa Craig Sweet Onion
Allium cepa 'Ailsa Craig'
Ailsa Craig Sweet Onion is a reliable heirloom variety prized for its mild flavor and excellent storage life. Gardeners grow this allium to enjoy fresh bulbs in salads or cooked dishes throughout the cooler months of the growing season.
📷 Wikimedia CommonsStarting Ailsa Craig Sweet Onion: indoors or direct sow?
🏠 Start indoors 6 weeks before your last spring frost, then move the seedlings outside.
Start seeds indoors six weeks before the last frost date, then harden off seedlings gradually before moving them to their final outdoor location.
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 six weeks before your last spring frost date. Plant them one inch deep in seed trays; germination typically occurs within seven to fourteen days once conditions are favorable.
Space seedlings four to six inches apart after transplanting outdoors. These onions do not require support or trellising. Maintain consistent moisture by providing about an inch of water weekly, especially during bulb development. Apply a light mulch around the base to retain soil moisture and suppress weeds.
Watch for onion maggots, thrips, aphids, and cutworms; use row covers or hand-picking to manage them early. Prevent downy mildew, purple blotch, neck rot, and pink root by ensuring good air circulation and avoiding overhead watering. Harvest bulbs 110-120 days after sowing when tops fall over.
When to Plant Ailsa Craig Sweet 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 Sweet Onion
✓ Good companions
Onions repel cabbage worms, flea beetles, and other crucifer pests
Onions repel carrot flies while carrots help break up soil for onion bulb development
Onions provide pest protection while lettuce acts as living mulch for shallow onion roots
Both plants repel nematodes and work synergistically to deter various garden pests
Attracts beneficial insects while onions provide pest protection, compatible root systems
Onions deter aphids and other soft-bodied insects that attack pepper plants
Onions repel slugs, aphids, and other pests that commonly damage strawberry plants
Onions deter aphids, whiteflies, and hornworms from tomato plants
✗ Keep away from
Onions can slow asparagus growth and interfere with spear production
Onions can inhibit nitrogen fixation in bean roots and stunt legume growth
Allelopathic compounds from onions interfere with pea germination and root development
Nutrition Facts
Per 100g serving (USDA FoodData Central)
