Growing Onions from Seed Indoors: Varieties, Day Length, and Tips

Seed starting has begun at our house—the first vegetables we start indoors are onions and shallots.

Sure, we could buy onion sets, but variety choice is limited—mostly 'Stuttgarter' or 'Ebenezer', often forming thick-necked onions that bolt instead of forming firm bulbs.

Which Onion Is Right for You?

Growing from seed offers the widest range: reds, yellows, whites; round, flat, long; mild/sweet or pungent/tangy.

Seed-grown onions store better and are less likely to bolt.

Onion seeds need indoor starts in cold climates—they require soil >50°F to germinate. We plant 2 seeds per cell, grow inside until weather warms for transplanting. Easier to separate two plants than teasing many from a crowded flat.

Long-Day or Short-Day Onions?

Onions are photoperiodic—sensitive to daylight. When days reach 12+ hours, leaf production stops and bulbing begins. Farther north = longer summer days, so different varieties are bred for different regions. Imagine a line from the NC/SC border to San Francisco (~36° latitude). North of it: plant long-day types; south: short-day onions.

Long-Day Onion Varieties

• 'Walla-Walla' or 'Ailsa Craig' for huge onions.
• 'Red Wing', 'Red Florence', 'Southport Red' for good reds.
• 'Copra', 'Yellow Globe', 'Sweet Sandwich' for good keepers.

Short-Day Onion Varieties

• 'Yellow Granex' for sweet Vidalia-types.
• 'Texas 1015-Y Supersweet' or 'Red Creole' store well.
• 'White Bermuda' for mild onions.

What About Day-Neutral Onion Varieties?

Day-neutral onions don't care about day length, producing excellent crops anywhere. Some catalogs call them intermediates.

Good day-neutrals:

• 'Super Star'—mild white, large sweet bulbs.
• 'Candy'—yellow, stores well, can reach softball size.
• 'Red Stockton'—large, globe-shaped red, stores well.

All onions appreciate early starts since temperature and day length trigger bulbing. Cool weather encourages heavy leaf growth—get onions growing before heat hits. Young plants tolerate light frost.

In the South, plant fall onions to overwinter for a head start—harvest in May.

Onions prefer sweet, fertile, near-neutral pH soil with lots of sun. Sulfur for bite comes from soil sulfur. Shallow-rooted—keep well-weeded, mulch to keep soil cool/moist. Best after lettuce or squash; poor after cole crops.

Known as "stinking lilies" but essential in every cuisine—no good cook would be without them.