Sierra Blanca

Family: Amaryllidaceae Vegetable

Planting Schedule

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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

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Sierra Blanca 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	Mar 30th	May 18th	Aug 11th – Aug 29th
Zone 2b	Mar 20th	May 8th	Aug 1st – Aug 25th
Zone 3a	Mar 20th	May 8th	Aug 1st – Sep 1st
Zone 3b	Mar 24th	May 12th	Aug 5th – Sep 21st
Zone 4a	Mar 20th	May 8th	Aug 1st – Sep 24th
Zone 4b	Mar 18th	May 6th	Jul 30th – Sep 27th
Zone 5a	Mar 13th	May 1st	Jul 25th – Sep 30th
Zone 5b	Mar 9th	Apr 27th	Jul 21st – Oct 5th
Zone 6a	Mar 6th	Apr 24th	Jul 18th – Oct 10th
Zone 6b	Feb 28th	Apr 18th	Jul 12th – Oct 16th
Zone 7a	Feb 23rd	Apr 13th	Jul 7th – Oct 20th
Zone 7b	Feb 13th	Apr 3rd	Jun 27th – Oct 28th
Zone 8a	Feb 4th	Mar 25th	Jun 18th – Nov 5th
Zone 8b	Jan 26th	Mar 16th	Jun 9th – Nov 12th
Zone 9a	Jan 9th	Feb 27th	May 23rd – Nov 26th
Zone 9b	Dec 15th	Feb 2nd	Apr 28th – Dec 9th
Zone 10a	—	Oct 1st	Dec 25th – Feb 28th
Zone 10b	—	Oct 1st	Dec 25th – Feb 28th
Zone 11a	—	Oct 1st	Dec 25th – Feb 28th
Zone 11b	—	Oct 1st	Dec 25th – Feb 28th
Zone 12a	—	Oct 1st	Dec 25th – Feb 28th
Zone 12b	—	Oct 1st	Dec 25th – Feb 28th
Zone 13a	—	Oct 1st	Dec 25th – Feb 28th
Zone 13b	—	Oct 1st	Dec 25th – Feb 28th

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.