Sierra Blanca

Family: Amaryllidaceae Vegetable

A luminous, snow-white bulb with a gentle, sweet allure—Sierra Blanca is the kind of onion that feels mellow from the first slice, with a tender bite and a clean, aromatic finish.

Bulbs form with an elegant, globe-to-flat silhouette and a smooth, papery skin that keeps beautifully while staying pleasantly crisp in storage. Grow Sierra Blanca for fresh, sweet-forward use and for roasting, where its natural sugars turn silky and fragrant—ideal for gardeners who want white onions that taste as good as they look.

Light: Full SunMaturity: 85 DaysHabit: Bulbing

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

Crop Dates

Milestone	Date
Start Indoors	Feb 28th
Last Frost	Apr 25th
Transplant / Sow Outdoors	Apr 18th
Harvest Begins	Jul 12th
Harvest Ends	Oct 16th

Crop Details

Trait	Value
Days to Maturity	85
Sun Requirements	Full Sun
Growth Habit	Bulbing
Support Needed	None
Planting Depth	Normal
Germination Temp (°F)	70
Min Soil Temp (°F)	45
Min Night Temp (°F)	28
Harden Off (days)	7

Culinary Notes

Chef's Note

Sierra Blanca is built for the sweet side of onion—its lower bite makes it welcome raw, while its sugar load turns luxurious and silky when roasted. Slice it thin for crispness that doesn’t burn the palate, or give it heat to coax out that snow-white, fragrant softness.

Best Uses

caramelize for a glossy, gentle sweetness
roast whole or in thick wedges for silky, sugar-softened edges
raw in thin slices for crisp, sweet crunch on salads or tostadas
quick-pickle or lightly cook into relishes where you want flavor without sting

Flavor Profile

mellow sweetness tender snap with low harsh bite clean, aromatic allium finish

Kitchen Pairings

balsamic vinegar thyme goat cheese butter black pepper chicken stock

Frequently Asked Questions

What are the most common onion problems (Allium cepa) like Sierra Blanca, and how do I treat them?

Watch for purple blotch (Alternaria porri) and downy mildew, which show up as blotches or fuzzy gray-purple growth on leaves during humid weather. Remove and discard badly affected leaves, avoid wetting the foliage, and improve airflow; for home gardens you can switch to a labeled onion fungicide and repeat per label directions when conditions stay damp. Keep onion beds weed-free and don’t over-fertilize with nitrogen, which encourages tender foliage that diseases attack.

How often should I water Allium cepa during the main growing phase?

During active bulbing (roughly mid-season through about 2–3 weeks before harvest), keep soil consistently evenly moist but not waterlogged—about 1 inch of water per week, split into 2–3 waterings if it’s hot and fast-draining. When the top growth is established, check moisture 1–2 inches down; if it’s dry at that depth, water again. Stop regular watering once bulbs start to size and tops begin to fall over, so skins can dry properly.

How can I tell when Sierra Blanca (Allium cepa) is ready to harvest?

Harvest when about 50–70% of the tops have fallen over and the necks are beginning to soften, typically around 85 days from planting. Lift a bulb and look for papery outer skins and a firm bulb with minimal springiness when squeezed. If skins aren’t papery yet, wait a few more days—delaying harvest slightly can improve storage quality.