Heirloom

Ailsa Craig Onion

Allium cepa

A distinct strain of the classic sweet and mild Ailsa Craig, this line has been specifically selected to perform in organic management systems. Mild onion with excellent size potential. Jumbo to colossal, round to teardrop-shaped bulbs with light yellow skins. Use fresh or for short-term storage. Adaptation: 38-60° latitude. Also available with NOP-compliant pelleting. USDA Certified Organic.

Harvest

110d

Days to harvest

📅

Sun

Full sun

☀️

Zones

5–10

USDA hardiness

🗺️

Height

12-18 inches

📏

Planting Timeline

Zone:

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Direct Sow

Harvest

Direct Sow

Harvest

Showing dates for Ailsa Craig Onion in USDA Zone 7

All Zone 7 root-vegetable →

Zone Map

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Ailsa Craig Onion · Zones 5–10

What grows well in Zone 7? →

Growing Details

Difficulty

Moderate

Spacing4-6 inches apart, rows 12-18 inches apart

SoilRich, well-drained loam with high organic matter

pH6.0-7.0

Water1-1.5 inches per week, reduce watering as bulbs mature

SeasonCool to warm season, long growing period

FlavorSurprisingly mild and sweet for such a large onion, with low sulfur content

ColorPale yellow to golden brown papery skin, white flesh

Size4-6 inches diameter, can reach 8+ inches

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

After proper curing, store Ailsa Craig onions in a cool, dry location with good air circulation at 32-40°F with 65-70% humidity. Properly cured bulbs will keep 4-6 months in ideal conditions. Avoid storing in plastic bags or humid environments, which promote rot. Check stored onions monthly and remove any showing soft spots or sprouting.

For preservation, these large onions are excellent for freezing when diced – blanch for 2 minutes before freezing for best texture. They're also perfect for making French onion soup that can be frozen in portions. Due to their size and mild flavor, they're ideal for pickling in large chunks or rings. Avoid dehydrating unless sliced very thin, as their high moisture content makes drying challenging.

History & Origin

Ailsa Craig onion takes its name from the distinctive volcanic island off Scotland's Ayrshire coast, visible from the mainland as a dramatic cone rising from the sea. This heirloom variety was developed in the late 1800s by Scottish gardeners who prized both size and flavor in their exhibition onions. The variety gained fame in British horticultural circles during the Victorian era when competitive vegetable growing reached its peak.

The onion's reputation spread throughout the British Isles as gardeners discovered it could produce massive bulbs exceeding 2 pounds while maintaining remarkable sweetness. Unlike many giant vegetables that sacrifice flavor for size, Ailsa Craig's mild, sweet character made it valuable for both competition and cuisine. It became a staple in Scottish gardens and eventually made its way to North America with Scottish immigrants, where it continues to be treasured by both exhibition gardeners and home cooks seeking an onion that delivers both impressive size and exceptional taste.

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 tomato hornworms and aphids, while tomatoes don't compete for nutrients

Lettuce

Shallow-rooted lettuce doesn't compete with onions and benefits from onion's pest-repelling properties

Brassicas

Onions repel cabbage worms, flea beetles, and other brassica pests

Peppers

Onions deter aphids and other soft-bodied insects that attack pepper plants

Strawberries

Onions repel slugs and other pests while improving strawberry flavor

Marigolds

Both repel similar pests and marigolds add extra nematode control

Parsley

Attracts beneficial insects and doesn't compete for space or nutrients

Keep Apart

Beans

Onions can inhibit bean growth and nitrogen fixation by rhizobia bacteria

Peas

Onions stunt pea growth and interfere with their nitrogen-fixing capabilities

Asparagus

Both compete for similar soil nutrients and can inhibit each other's growth

Nutrition Facts

Calories

40kcal(2%)

Protein

1.1g(2%)

Fiber

1.7g(6%)

Carbs

9.34g(3%)

Fat

0.1g(0%)

Vitamin C

7.4mg(8%)

Vitamin A

0mcg(0%)

Vitamin K

0.4mcg(0%)

Iron

0.21mg(1%)

Calcium

23mg(2%)

Potassium

146mg(3%)

Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #170000)

Pests & Disease Resistance

Resistance

Moderate resistance to downy mildew and neck rot

Common Pests

Onion thrips, onion maggot, cutworms

Diseases

Downy mildew, purple blotch, neck rot, white rot

Frequently Asked Questions

How big do Ailsa Craig onions actually get?▼

Ailsa Craig onions regularly reach 1-2 pounds with proper growing conditions, and exceptional specimens can exceed 3 pounds. Most home gardeners can expect bulbs in the 12-16 ounce range, which is still significantly larger than typical storage onions. The key to maximum size is starting seeds early indoors, providing rich soil, consistent moisture, and a full growing season.

Can you grow Ailsa Craig onions in containers?▼

Yes, but use containers at least 12 inches deep and wide to accommodate the large bulb development. Choose a 20-gallon container for best results, using rich potting mix amended with compost. Container-grown bulbs may be smaller than garden-grown ones, typically reaching 8-12 ounces, but will still maintain the characteristic mild, sweet flavor that makes this variety special.

Is Ailsa Craig good for beginners?▼

Ailsa Craig is moderately challenging and better suited for gardeners with some experience. The long growing season, early indoor seed starting, and heavy feeding requirements make it more demanding than typical onion varieties. Beginners should start with easier varieties like Yellow Sweet Spanish before attempting this exhibition-type onion.

When should I start Ailsa Craig onion seeds?▼

Start seeds indoors 10-12 weeks before your last frost date. For most zones, this means starting in late January to early March. The long lead time is crucial for achieving maximum bulb size, as Ailsa Craig needs the full growing season to develop its characteristic large bulbs.

What does Ailsa Craig onion taste like?▼

Ailsa Craig has a surprisingly mild, sweet flavor with low sulfur content, making it much gentler than typical large onions. The taste is often described as buttery and sweet when cooked, with minimal sharpness when eaten raw. This makes it excellent for caramelizing, stuffing, or eating fresh in salads despite its impressive size.

Ailsa Craig vs Walla Walla onions - what's the difference?▼

Both are large, mild onions, but Ailsa Craig is a long-season storage variety that keeps 4-6 months, while Walla Walla is a short-day onion best used fresh. Ailsa Craig grows larger (often 2+ pounds vs Walla Walla's 1 pound average) and has better disease resistance, but Walla Walla is easier to grow and ready earlier in the season.