White Castle

Family: Amaryllidaceae Vegetable

Sweetly mild and serenely aromatic, White Castle onions develop into crisp, snow-white bulbs with a clean, glassy skin that peels away in satisfying layers.

The flesh is tender and juicy, offering a gentle bite that shines in fresh applications and rewards slow roasting until mellow and golden. Grow White Castle for a dependable 120-day season and a harvest that stores with confidence for weeks of flavorful versatility.

Light: Full SunMaturity: 120 DaysHabit: Bulbing

Planting schedules and alerts are optimized for Columbus (Zone 6b).

Crop Dates

Milestone	Date
Start Indoors	Direct Sow
Last Frost	Apr 25th
Transplant / Sow Outdoors	Apr 18th
Harvest Begins	Aug 16th
Harvest Ends	Oct 16th

Crop Details

Trait	Value
Days to Maturity	120
Sun Requirements	Full Sun
Growth Habit	Bulbing
Support Needed	None
Planting Depth	Normal
Germination Temp (°F)	65
Min Soil Temp (°F)	45
Min Night Temp (°F)	35
Harden Off (days)	7

Culinary Notes

Chef's Note

White Castle is built for the “don’t overwhelm me” kind of onion—tender, juicy, and sweetly mild, so it stays crisp raw and turns silky without going acrid. Roast it low and slow until golden and it becomes almost custardy inside, perfect for letting butter, thyme, and cheese do the talking.

Best Uses

raw shaved salad or slaws where the layers stay snappy
caramelized onions that stay creamy rather than sharp
slow-roasted wedges for a jammy, golden core
thin-sliced onion rings or batter frying for a gentle sweetness

Flavor Profile

sweet-mild allium bite juicy, tender crunch serenely aromatic with mellowing heat clean, crisp finish

Kitchen Pairings

butter thyme black pepper gruyère chicken stock balsamic vinegar

Frequently Asked Questions

What pest or disease commonly affects Allium cepa (white onions), and how can I control it?

Onions (Allium cepa) are commonly hit by purple blotch (Alternaria porri) and downy mildew, which show up as purple/gray lesions on leaves and can reduce bulb size. Remove and destroy infected foliage promptly, water at the base to keep leaves dry, and improve airflow by thinning so plants aren’t crowded. If problems persist, use an onion-safe fungicide labeled for purple blotch/downy mildew and start treatments at the first leaf symptoms.

How often should I water Allium cepa during the main growing phase, and what soil moisture target should I maintain?

During the main bulbing period, keep the soil evenly moist but not soggy—aim for about 1 inch (2.5 cm) of water per week, split into 1–2 deep waterings depending on rainfall. Water when the top 1 inch of soil feels dry, especially during dry spells, because inconsistent moisture can lead to stalled growth or split/poorly formed bulbs. Stop regular watering as leaves begin to yellow and fall over, so bulbs cure and store better.

How do I know when white onions (Allium cepa) are ready to harvest?

Harvest when about 50–75% of the tops have turned yellow and started to flop, and the bulb skin feels papery and firm when gently squeezed. Avoid harvesting too early, because underdeveloped onions won’t cure well for storage. Lift bulbs carefully (don’t pull hard enough to damage skins), then cure them in a dry, airy spot out of direct sun before storing.