Ailsa Craig Onion (Exhibition onion) care

Light

Aim for at least 4-6 hours of direct sun on the leaves. Requires full sun — minimum 6 hours daily. Long summer days trigger bulb initiation; siting in full light maximises bulb size and ripening. If your only bright window faces south, that's perfect for ailsa craig onion — same window any aroid would fry on.

Watering

Crops like ailsa craig onion reward consistent watering — water regularly during active growth (spring–early summer); reduce once the tops begin to fall in mid-summer. The mistake is the daily light sprinkle: it never reaches the deeper roots. A long soak twice a week beats a five-minute splash every day. Consistent moisture from planting to midsummer supports good bulb development. As bulbs swell and foliage yellows, withhold water to aid ripening and curing. Avoid waterlogged soil at all times.

Soil and pot

Ailsa Craig Onion grows best in fertile, well-drained, deeply dug loam. Prepare the bed with well-rotted compost or manure in autumn. Onions need firm, settled soil — avoid freshly manured ground. pH 6.5–7.0 is optimal; lime if necessary. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Ailsa Craig Onion sits happiest at around 40-60% humidity and 10-25°C (50-77°F). Moderate humidity is fine during growth. Reduce humidity at ripening/curing stage to prevent neck rot and downy mildew. Good air circulation is important. If you keep the room above 10 year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed ailsa craig onion sparingly. Apply a balanced general-purpose fertiliser or blood, fish and bone at planting. Top-dress with a nitrogen-rich feed (e.g. sulphate of ammonia) in early spring for strong leaf growth, but stop all feeding by midsummer to allow bulb ripening. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on ailsa craig onion in the Growli community. Each is annotated with the most common cause so you know where to start.

• Onion white rot — Sclerotinia cepivorum causes fluffy white fungal growth at the bulb base. No chemical cure; remove and destroy affected plants; do not grow alliums in the same bed for 8+ years.
• Onion fly — Larvae tunnel into bulbs, causing wilting and rotting. Cover with fine insect mesh from sowing to midsummer.
• Downy mildew — Peronospora destructor causes grey-purple fuzz on leaves in wet weather. Improve air circulation; avoid overhead watering.
• Bolting — Premature seed-head formation, especially after a cold period followed by warmth. Remove seed heads promptly; use bolt-resistant sets or sow at the correct time.
• Neck rot (Botrytis allii) — Soft rot at the neck during storage. Ensure bulbs are fully cured in the sun before storing; store in a cool, dry, airy place.

Companion plants

Ailsa Craig Onion pairs well with Carrot, Beetroot, Lettuce, and Chamomile. These are species with similar light and water needs, so you can grow them in the same bed or container without conflict.

Propagation

Sow seed in January-February in heated propagator (15°C) or directly outdoors from March. Thin to 15-30 cm apart for standard bulbs or 30 cm for exhibition specimens. Can also be grown from sets (small bulbs) planted in spring or autumn. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Ailsa Craig Onion is toxic to pets. The ASPCA lists Allium species (onions, garlic, chives, leeks) as toxic to dogs, cats, and horses. All plant parts contain organosulfur compounds that cause dose-dependent haemolytic anaemia; clinical signs include lethargy, pale gums, and vomiting. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Ailsa Craig Onion deep-dive guides

Every aspect of ailsa craig onion care, each with its own calibrated guide:

• Common ailsa craig onion problems & fixes
• Ailsa Craig Onion watering schedule
• Ailsa Craig Onion light requirements
• Best soil mix for ailsa craig onion
• Ailsa Craig Onion fertilizing guide
• When to repot ailsa craig onion
• How to propagate ailsa craig onion
• How to prune ailsa craig onion
• What's eating my ailsa craig onion?
• Ailsa Craig Onion growth rate & size
• Ailsa Craig Onion cold hardiness
• Ailsa Craig Onion temperature & humidity
• Is ailsa craig onion toxic to cats & dogs?
• Is ailsa craig onion toxic to cats?
• Is ailsa craig onion toxic to dogs?
• All 30 Allium varieties

Related guides

Ailsa Craig Onion is also known as Exhibition onion, Ailsa Craig, and Show onion.

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• All 11687 plant care guides in the Growli library