Sierra Blanca

Onion

Zone 8a Save Garden

🌱 85d to harvest Bulbing

A luminous, snow-white bulb with a gentle, sweet allure—Sierra Blanca is the kind of onion that feels mellow from the first slice…

Crop Dates

Milestone	Date
Start Indoors	Feb 4th
Last Frost	Apr 1st
Transplant / Sow Outdoors	Mar 25th
Harvest Begins	Jun 18th
Harvest Ends	Nov 5th

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

Recommended Companions

Imperial 615 Lettuce

Lollo Di Vino Lettuce

Yellowstone Carrot

Detroit Dark Red Beet

Lollo Rosso Darky Lettuce

Tonda di Parigi Carrot

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.

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.

Sowing Tips

Transplant Conditions

Wait until soil reaches 45°F and nights stay above 28°F before moving outdoors. Harden off for 7 days first.

Expert Note

For sweet, mild bulbs, keep soil moisture consistent and avoid heavy nitrogen later in the season so bulbs can mature and cure well.