Growing guide

How to Grow Onions

Day-length-driven bulbs — choosing the right type for your latitude is everything.

The basics

What onions need

• Sun — Full sun
• Water — 1 inch per week; stop as tops fall
• Harvest in 90–120 days
• Difficulty — Moderate

When to plant

Time it from your frost date

• Start indoors: 8–10 weeks before last frost
• Transplant: As soon as soil is workable
• Direct sow: Sets or seed in early spring
• Best in Zones 3–9 (choose day-length type for your…

How to plant

Three steps to a strong start

• 1. Choose long-day (North), short-day (South), or day-neutral types to match your latitude.
• 2. Start seed indoors 8–10 weeks early, or plant sets/transplants in early spring.
• 3. Set out pencil-thick transplants 4 in apart as soon as soil can be worked.

Common problem

Small bulbs

Wrong day-length type for your latitude, or crowding/weed competition.

Common problem

Bolting (flower stalks)

From cold stress on large transplants/sets — use smaller sets and avoid early cold snaps.

Harvest

Picking onions right

When most tops have flopped over and started to brown, lift the bulbs and cure them in a dry, airy place for 2–3 weeks until the necks are papery. Then trim and store.

Gardeners ask

What are long-day and short-day onions?

They bulb at different day lengths. Long-day onions suit northern gardens, short-day the South, and day-neutral types work in between.

Keep growing

Get the full Onions guide

Planting dates for your USDA zone, spacing, companions, every common problem — free on Plants by Zone.

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