White Castle

Family: Amaryllidaceae Vegetable

Planting Schedule

Provide your location or planting zone to unlock dates and add White Castle to a garden.

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

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White Castle Planting Dates by USDA Zone

Estimated US hardiness-zone windows for sow, transplant, and harvest. Enter a US ZIP above for exact local dates, or open a zone below.

Zone	Start Indoors	Sow / Transplant	Harvest
Zone 1a	Protected Environment Only
Zone 1b	Protected Environment Only
Zone 2a	Protected Environment Only
Zone 2b	Protected Environment Only
Zone 3a	Protected Environment Only
Zone 3b	Direct Sow	May 12th	Sep 9th – Sep 21st
Zone 4a	Direct Sow	May 8th	Sep 5th – Sep 24th
Zone 4b	Direct Sow	May 6th	Sep 3rd – Sep 27th
Zone 5a	Direct Sow	May 1st	Aug 29th – Sep 30th
Zone 5b	Direct Sow	Apr 27th	Aug 25th – Oct 5th
Zone 6a	Direct Sow	Apr 24th	Aug 22nd – Oct 10th
Zone 6b	Direct Sow	Apr 18th	Aug 16th – Oct 16th
Zone 7a	Direct Sow	Apr 13th	Aug 11th – Oct 20th
Zone 7b	Direct Sow	Apr 3rd	Aug 1st – Oct 28th
Zone 8a	Direct Sow	Mar 25th	Jul 23rd – Nov 5th
Zone 8b	Direct Sow	Mar 16th	Jul 14th – Nov 12th
Zone 9a	Direct Sow	Feb 27th	Jun 27th – Nov 26th
Zone 9b	Direct Sow	Feb 2nd	Jun 2nd – Dec 9th
Zone 10a	—	Oct 1st	Jan 29th – Feb 28th
Zone 10b	—	Oct 1st	Jan 29th – Feb 28th
Zone 11a	—	Oct 1st	Jan 29th – Feb 28th
Zone 11b	—	Oct 1st	Jan 29th – Feb 28th
Zone 12a	—	Oct 1st	Jan 29th – Feb 28th
Zone 12b	—	Oct 1st	Jan 29th – Feb 28th
Zone 13a	—	Oct 1st	Jan 29th – Feb 28th
Zone 13b	—	Oct 1st	Jan 29th – Feb 28th

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.