How to Choose the Right Onion Varieties

Onion Day Length

Onion Daylength Reference

The right onion starts with the right daylength.

Onion varieties begin forming bulbs in response to hours of daylight. Knowing your growing region helps narrow the choice between long-day, intermediate-day, and short-day varieties.

Start With Your Location

Find your region on the map.

Northern areas typically favor long-day onions, middle states intermediate-day types, and southern regions short-day varieties.

Transition areas may support more than one daylength type depending on location and planting schedule.

Daylength Comparison

Northern States

Long-Day

37°–47° latitude

Needs approximately 14–16 hours of daylight to initiate bulbing.

Generally better suited for northern regions and often for longer storage.

Middle States

Intermediate-Day

32°–42° latitude

Needs approximately 12–14 hours of daylight to initiate bulbing.

Useful throughout much of the middle United States and often very sweet.

Southern States

Short-Day

25°–35° latitude

Needs approximately 10–12 hours of daylight to initiate bulbing.

Earlier planting gives the plant more time to develop before bulb formation.

Why It Matters

Give the plant enough growing time before bulb formation begins.

Selecting an onion suited to your latitude helps bulb formation begin at the appropriate point in the season. A poorly matched daylength type may bulb before the plant has developed enough foliage to produce the size you expect.

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