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A freshly pulled White Sweet Spanish onion showing its large white globe bulb and roots

How to Grow White Sweet Spanish Onions From Seed

By Maxim Kaufman — Founder & CEO, Organo Republic

Updated July 2026

White Sweet Spanish is a large, mild white onion that forms handsome round globes with clean white flesh and a sweet, gentle flavor. It is a long-day variety, so it sizes up best for Northern gardeners with long summer days. Here is what makes this variety special and how to get the best from it.

This is the quick guide to White Sweet Spanish. For the full step-by-step on starting seeds, sowing, feeding, and troubleshooting onions, see our complete guide to growing onions from seed.

Quick start

Start seeds indoors 8 to 10 weeks before your last frost, then transplant seedlings 4 to 6 inches apart in full sun and rich, well-drained soil. Keep the bed weed-free and evenly watered, feeding until the bulbs swell. Harvest in about 110 days when the tops flop over and begin to dry.

Best tip

White Sweet Spanish is a long-day onion, so it bulbs best in the North where summer days are long; Southern gardeners will get better results from a short-day type. Give it a long, early indoor start and steady feeding for the biggest globes, and cure it well if you want it to keep for a few months.

At a glance

Botanical nameAllium cepa

Plant typeLong-day sweet onion

USDA zones3 to 9 (grown as an annual)

SunFull sun (6 or more hours)

Days to maturity110 days

Height12 to 20 inches

Spacing4 to 6 inches apart

WaterSteady and even; about 1 inch a week

Uses

White Sweet Spanish is a versatile mild white onion. Its sweet flavor works raw in salads, salsas, and sandwiches, and it cooks down beautifully in soups, sauces, and stir-fries. It stores moderately well when cured, giving you crisp white onions into fall.

Frequently asked questions

How long does White Sweet Spanish onion take to grow?

About 110 days from transplant, plus roughly 8 to 10 weeks of indoor growing beforehand.

Is White Sweet Spanish a long-day or short-day onion?

It is a long-day onion, so it needs the long summer days of northern latitudes to bulb up well. In the South it may stay small.

How well do White Sweet Spanish onions store?

They store moderately, better than very sweet types but not as long as pungent yellow keepers. Cure them well and use them within a few months.

How big do White Sweet Spanish onions get?

They form large, round white globes, often 3 to 4 inches across when grown with room, steady water, and feeding.

Ready to grow your own? Our 8 Onion Variety Pack lets you grow White Sweet Spanish alongside seven other onions from a single order. For the full step-by-step, see our complete onion growing guide linked at the top of this page.

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By Maxim Kaufman — Founder & CEO, Organo Republic

Maxim founded Organo Republic in 2017 and personally selects, tests, and grows the heirloom, non-GMO varieties the company offers. Under his leadership, Organo Republic was named Agri Business Review’s Top Non-GMO Seed Variety Solution 2026.