Grown Ailsa Craig Sweet Onion?

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Ailsa Craig Sweet Onion — Onions & alliums

110-120days to harvest

7-14days to germinate

Z5–10USDA zones

Moderate to challengingdifficulty

Heirloom

Sowing

Start seeds indoors 10-12 weeks before last frost. Transplant when soil can be worked and plants are pencil-thick.

Cultivation

Sun: Full sun (6+ hours)
Water: 1 inch per week, consistent moisture during bulb development
Soil: Rich, well-drained loam with high organic content
Soil pH: 6.0-7.0
Spacing: 4-6 inches
Height: 12-18 inches
Season: Cool season

Appearance & flavour

Colour: Pale yellow to golden skin with white flesh
Size: 4-6 inches diameter, 1-3 pounds
Shape: Large globe, slightly flattened
Flavour: Sweet and mild with low sulfur content

In the kitchen

Excellent for fresh eating, salads, sandwiches, light cooking. Too mild for strong flavoring applications.

Pests, disease & resistance

Pests: Onion maggot, thrips, aphids, cutworms
Diseases: Downy mildew, purple blotch, neck rot, pink root
Resistance: Moderate resistance to pink root and fusarium basal rot

Planting calendar by USDA zone

Zone	Start indoors	Transplant	Direct sow	Harvest
1	—	—	June – July	September
2	—	—	May – July	September
3	—	—	May – June	August – October
4	—	—	April – June	August – October
5	—	—	April – May	August – November
6	—	—	April – May	July – November
7	—	—	March – May	July – November
8	—	—	March – April	June – December
9	—	—	February – March	May – December
10	—	—	January – March	May – December
11	—	—	January – February	April – December
12	—	—	January – February	April – December
13	—	—	January – February	April – December

Companion planting

8 beneficial pairings indexed for this variety, 3 to avoid.

CarrotsOnions repel carrot flies while carrots help break up soil for onion bulb development

TomatoesOnions deter aphids, whiteflies, and hornworms from tomato plants

Brassicas (Cabbage, Broccoli)Onions repel cabbage worms, flea beetles, and other crucifer pests

LettuceOnions provide pest protection while lettuce acts as living mulch for shallow onion roots

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

StrawberriesOnions repel slugs, aphids, and other pests that commonly damage strawberry plants

MarigoldsBoth plants repel nematodes and work synergistically to deter various garden pests

ParsleyAttracts beneficial insects while onions provide pest protection, compatible root systems

Avoid

BeansOnions can inhibit nitrogen fixation in bean roots and stunt legume growth

PeasAllelopathic compounds from onions interfere with pea germination and root development

AsparagusOnions can slow asparagus growth and interfere with spear production

Nutrition (per 100 g)

Calories (per 100 g): 40
Protein (g): 1.1
Fat (g): 0.1
Carbohydrate (g): 9.34
Fibre (g): 1.7
Sugars (g): 4.24
Vitamin A (µg): 0
Vitamin C (mg): 7.4
Vitamin E (mg): 0.02
Vitamin K (µg): 0.4
Vitamin B6 (mg): 0.12
Folate (µg): 19
Calcium (mg): 23
Iron (mg): 0.21
Magnesium (mg): 10
Phosphorus (mg): 29
Potassium (mg): 146
Zinc (mg): 0.17
Selenium (µg): 0.5

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Where to buy seed and equipment

Some links are affiliate links. If you buy through them we may earn a commission at no extra cost to you.

Growing it? There is a full cultivation guide at the onions & alliums growing guide.

Cultivar facts compiled from public horticultural references including USDA GRIN and NC State Extension. Descriptions are original to this catalogue.

Sowing

Cultivation

Appearance & flavour

In the kitchen

Pests, disease & resistance

Planting calendar by USDA zone

Companion planting

Avoid

Nutrition (per 100 g)

Where to buy seed and equipment

Grown Ailsa Craig Sweet Onion?

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