Onion | Spanish 'Ailsa Craig'

Grow impressive, sweet, and mild globe-shaped Ailsa Craig onions in your home garden. This classic heirloom onion is prized for its exceptional size, beautiful golden-straw skin, and deliciously mild, sweet white flesh. Perfect for fresh slicing, salads, sandwiches, and everyday cooking, Ailsa Craig is a favourite among gardeners who appreciate large, flavourful homegrown onions.

These productive plants develop substantial, rounded bulbs when provided with a long growing season and favourable conditions. Start seeds indoors during late winter to give plants a strong head start before transplanting outdoors in spring. Well suited to Canada's long summer daylight hours, Ailsa Craig is a rewarding choice for gardeners looking to grow impressive, sweet onions from seed.

Why Grow Ailsa Craig Onions?

• Impressive, large, globe-shaped bulbs with beautiful golden-straw skin
• Deliciously mild, sweet flavour ideal for fresh slicing
• Productive plants capable of developing exceptionally large bulbs
• Classic open-pollinated heirloom onion variety
• Long-day variety well suited to many Canadian growing regions
• Approximately 100–110 days to maturity from transplanting
• Grows best in full sun
• Approximately 120–130 seeds per packet

How to Grow Ailsa Craig Onions from Seed

Start onion seeds indoors approximately 10–12 weeks before your last expected spring frost. Sow seeds in flats or trays filled with a well-draining seed-starting mix, covering them lightly with approximately 6 mm (¼ inch) of soil.

Keep the growing mix consistently moist during germination. Once seedlings emerge, provide 14–16 hours of bright light daily to encourage healthy growth. Onion seedlings naturally develop long, slender leaves, so occasional bending is normal. Trimming is generally unnecessary; focus on providing adequate light, moisture, and airflow.

Gradually harden off seedlings over 7–10 days before transplanting outdoors in early spring, once the soil can be worked and conditions are suitable. Choose a location with full sun and fertile, well-drained soil. Space plants approximately 10–15 cm (4–6 inches) apart, setting them at approximately their original growing depth without burying the developing bulb area too deeply.

Water consistently throughout active growth and bulb development, keeping the soil evenly moist without waterlogging. As bulbs approach maturity and the tops begin naturally yellowing and falling over, reduce watering to encourage proper maturation and curing.

Growing Onions in Canada

Ailsa Craig onions are well suited to Canadian gardens when started early indoors. As a long-day onion variety, Ailsa Craig benefits from Canada's extended summer daylight hours, which encourage bulb formation after the plants have developed healthy foliage.

For the largest possible bulbs, provide fertile soil, consistent moisture, sufficient spacing, and a weed-free growing area. Onions have relatively shallow root systems and compete poorly with weeds for water and nutrients.

Ailsa Craig is primarily valued as a large, mild, sweet onion for fresh use. Unlike varieties specifically bred for long-term winter storage, its high-moisture bulbs are best enjoyed relatively soon after harvest.

For detailed instructions covering seed starting, spacing, watering, fertilizing, harvesting, curing, and pest management, read our How to Grow Onions in Canada | Complete Growing Guide.

Ailsa Craig Onion Growing Information

Feature	Detail
Botanical Name	Allium cepa 'Ailsa Craig'
Common Name	Ailsa Craig Onion (Sweet Spanish Onion)
Plant Type	Biennial grown as an annual bulb crop
Sun Requirements	Full sun (6–8 hours of direct sunlight daily)
Days to Maturity	Approximately 100–110 days from transplanting
Seed Count	Approximately 120–130 seeds
Pollination Type	Open-pollinated heirloom variety
Best Uses	Fresh slicing, salads, sandwiches, burgers, roasting, and cooking

Grow Your Own Ailsa Craig Onions

There is nothing quite like harvesting impressive, sweet onions straight from your own garden. With their exceptionally mild flavour, beautiful golden-straw skin, and potential for producing large globe-shaped bulbs, Ailsa Craig onions are a rewarding addition to any Canadian vegetable garden.

Start your Ailsa Craig onion seeds indoors this season and enjoy growing delicious, homegrown onions that bring fresh flavour and versatility to your kitchen.