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A freshly pulled Eclipse onion showing its flattened white bulb and roots

How to Grow Eclipse Onions From Seed

By Maxim Kaufman — Founder & CEO, Organo Republic

Updated July 2026

Eclipse L303 is a mild, sweet onion that forms an attractive flattened white bulb with crisp, gentle flesh. It is an easy, productive variety that rewards steady care with clean, uniform onions. Here is what makes this variety special and how to get the best from it.

This is the quick guide to Eclipse L303. 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 about 8 to 10 weeks before your last frost, then transplant seedlings 4 to 6 inches apart in full sun and rich soil. Keep the bed evenly watered and weed-free, feeding until the bulbs begin to swell. Harvest in about 100 to 110 days once the tops flop and yellow.

Best tip

Grow Eclipse in full sun with steady moisture and feeding for the cleanest, sweetest flattened bulbs. Start seeds early indoors for a good head start, keep young plants out of hard cold spells to prevent bolting, and cure the bulbs after harvest if you want them to keep for a while.

At a glance

Botanical nameAllium cepa

Plant typeSweet onion

USDA zones3 to 9 (grown as an annual)

SunFull sun (6 or more hours)

Days to maturity100 to 110 days

Height12 to 18 inches

Spacing4 to 6 inches apart

WaterSteady and even; about 1 inch a week

Uses

Eclipse is a mild, sweet white onion that is lovely fresh. Slice it raw into salads and salsas, add it to sandwiches and burgers, or cook it down in everyday dishes where a gentle onion flavor is wanted. Cure the bulbs for moderate storage.

Frequently asked questions

How long does Eclipse onion take to grow?

About 100 to 110 days from transplant, plus roughly 8 to 10 weeks of indoor growing first.

What does an Eclipse onion look like?

It forms a distinctive flattened white bulb with crisp, mild white flesh, uniform and attractive for both kitchen and market.

Is Eclipse a sweet onion?

Yes, Eclipse is mild and sweet, good for fresh eating, with enough substance to cook well in everyday dishes.

How do I get the biggest Eclipse bulbs?

Give full sun, rich soil, 4 to 6 inches of spacing, and steady water and feeding while the tops grow, easing off once the bulbs swell.

Ready to grow your own? Our 8 Onion Variety Pack lets you grow Eclipse L303 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.

Eclipse L303 Onion Seeds – Non-GMO HeirloomHeirloom, non-GMOOnion Eclipse L303 — reliable storage onion with firm, long-keeping bulbs.

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Want more onions? These value packs pair sweet onions like Eclipse with other varieties:

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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.

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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.