Home / Growing Guides / How to Grow Yellow Sweet Spanish Onions From Seed

A freshly pulled Yellow Sweet Spanish onion showing its large yellow storage globe and roots

How to Grow Yellow Sweet Spanish Onions From Seed

By Maxim Kaufman — Founder & CEO, Organo Republic

Updated July 2026

Yellow Sweet Spanish (Utah strain) is a large, dependable yellow onion that forms big golden globes with firm, mildly sweet flesh and good keeping quality. It is a long-day variety, so it is a Northern-garden classic and one of the best all-around storage onions. Here is what makes this variety special and how to get the best from it.

This is the quick guide to Yellow 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 fall, then cure the bulbs well for storage.

Best tip

Yellow Sweet Spanish is a long-day onion that bulbs best in the North; Southern gardeners should pick a short-day type instead. For the best keepers, feed and water steadily while the tops grow, then stop once the bulbs size up and cure them thoroughly in a warm, airy spot before storing.

At a glance

Botanical nameAllium cepa

Plant typeLong-day storage 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

Yellow Sweet Spanish is the workhorse yellow onion for the kitchen. Big and firm with a mild, slightly sweet flavor, it is perfect for slicing, sauteing, caramelizing, and adding to soups, stews, and roasts. Well cured, it stores for several months, giving you onions well into winter.

Frequently asked questions

How long does Yellow Sweet Spanish onion take to grow?

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

Is Yellow Sweet Spanish a good storage onion?

Yes, it is one of the better-keeping sweet-leaning onions. Cure the bulbs well and they will store for several months in a cool, dry place.

Is Yellow Sweet Spanish long-day or short-day?

It is a long-day onion, so it needs the long summer days of the North to bulb well. It tends to stay small in the Deep South.

How big do Yellow Sweet Spanish onions get?

They grow into large golden globes, often 3 to 4 inches or more across when given room, steady water, and feeding.

Ready to grow your own? Our 8 Onion Variety Pack lets you grow Yellow 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.

Utah Yellow Sweet Spanish Onion Seeds – Non-GMO HeirloomHeirloom, non-GMOHeirloom Utah Yellow Sweet Spanish — big, mild yellow onion for all-purpose use.

Price$4.99

View product

Want more onions? These value packs pair storage onions like Yellow Sweet Spanish with other varieties:

Sale

Onion Seeds Variety Pack – Non-GMO Heirloom8 onion varietiesEight sweet, storage, and specialty onions in one pack — the easiest way to grow a whole spread of varieties from a single order.

Price$12.99 Sale Price$9.99

View product

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.