Ailsa Craig Sweet Onion
Allium cepa 'Ailsa Craig'
A legendary exhibition onion variety from Scotland that can grow to enormous sizes while maintaining sweet, mild flavor. This pale yellow globe onion is famous for winning competitions and producing bulbs that can weigh 2-3 pounds when grown with proper care. Despite its impressive size, Ailsa Craig maintains excellent eating quality and stores reasonably well.
Harvest
110-120d
Days to harvest
Sun
Full sun
Zones
5–10
USDA hardiness
Height
12-18 inches
Planting Timeline
Showing dates for Ailsa Craig Sweet Onion in USDA Zone 7
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Ailsa Craig Sweet Onion · Zones 5–10
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| 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 |
Complete Growing Guide
Light: Full sun (6 or more hours of direct sunlight a day). Soil: High Organic Matter, Loam (Silt), Sand. Soil pH: Alkaline (>8.0), Neutral (6.0-8.0). Drainage: Good Drainage, Moist. Height: 1 ft. 0 in. - 1 ft. 6 in.. Spread: 0 ft. 6 in. - 1 ft. 0 in.. Spacing: Less than 12 inches, 12 inches-3 feet. Maintenance: Medium. Regions: Coastal, Mountains, Piedmont.
Harvesting
Flowers wither and convert to bulblets
Type: Capsule.
Harvest time: Summer
Bloom time: Summer
Storage & Preservation
Cure freshly harvested Ailsa Craig bulbs in a warm (75-85°F), well-ventilated area for 2-3 weeks until the necks are completely dry and papery. Once cured, trim tops to 1 inch and store in mesh bags or shallow boxes in a cool (35-40°F), dry location with good air circulation.
Properly cured bulbs typically store 3-4 months—shorter than storage onions but respectable for a sweet variety. Check stored bulbs monthly and use any showing soft spots immediately.
For preservation, slice and freeze in portions for up to 8 months, though texture becomes soft when thawed. Dehydrate thin slices at 135°F for crispy onion chips, or pickle rings in mild vinegar brine to showcase their sweet flavor. Their mild nature makes them less suitable for strong pickled preparations.
History & Origin
Ailsa Craig Sweet Onion takes its name from the distinctive granite island off Scotland's Ayrshire coast, where it was first developed in the late 1800s. Scottish gardener David Murray is credited with creating this variety around 1887 on the island of Ailsa Craig, selectively breeding for the massive size and sweet flavor that would make it legendary among exhibition growers.
The variety gained fame in British horticultural shows during the Victorian era's golden age of competitive gardening, when enormous vegetables were prized symbols of gardening skill and estate prestige. Its reputation spread throughout the British Empire and eventually to North America through seed exchanges.
Ailsa Craig remains the gold standard for exhibition onions over 130 years later, with competition records showing individual bulbs exceeding 5 pounds. The variety represents the pinnacle of 19th-century selective breeding, achieving remarkable size while maintaining eating quality—a balance that many modern hybrids still struggle to match.
Advantages
- +Disease resistance: Black Walnut, Deer, Rabbits
Considerations
- -Toxic: Low severity
Companion Plants
Plant Together
Carrots
Onions repel carrot flies while carrots help break up soil for onion bulb development
Tomatoes
Onions deter aphids, whiteflies, and hornworms from tomato plants
Brassicas (Cabbage, Broccoli)
Onions repel cabbage worms, flea beetles, and other crucifer pests
Lettuce
Onions provide pest protection while lettuce acts as living mulch for shallow onion roots
Peppers
Onions deter aphids and other soft-bodied insects that attack pepper plants
Strawberries
Onions repel slugs, aphids, and other pests that commonly damage strawberry plants
Marigolds
Both plants repel nematodes and work synergistically to deter various garden pests
Parsley
Attracts beneficial insects while onions provide pest protection, compatible root systems
Keep Apart
Beans
Onions can inhibit nitrogen fixation in bean roots and stunt legume growth
Peas
Allelopathic compounds from onions interfere with pea germination and root development
Asparagus
Onions can slow asparagus growth and interfere with spear production
Nutrition Facts
Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #170000)
Pests & Disease Resistance
Resistance
Moderate resistance to pink root and fusarium basal rot
Common Pests
Onion maggot, thrips, aphids, cutworms
Diseases
Downy mildew, purple blotch, neck rot, pink root