Onions: Short Day vs. Long Day

Some plant types require a certain amount of sunlight to grow as we expect. Onions are a great example. You need to be conscious of your variety selection because they require a certain amount of day light hours to bulb.

For southern growers:

Sow short-day onion seed in late summer in rich soil with some light frost protection for overwintering. Transplant seedlings in late fall or winter and harvest onions in late spring, when 10 hr days promote bulbing.

Note: planting long day varieties in the south means you will never get any bulb development because there is not the requisite amount of light. However the greens are likely to be quite tasty!

For northern growers:

Sow long-day onion seed in flats in early spring in rich soil. Transplant seedlings in late spring and harvest onions in summer, when long days promote bulbing. Onions require evenly moist, well-drained soils, with minimal weed competition.

Note: planting short day onions in the north is likely to result in early bulb development before the top growth is developed enough to sustain the bulb, resulting in smaller bulbs.

Intermediate Day

Having a round earth means that short day and long day are two ends of a spectrum. In the middling states we are often borderline as to which onion type will work best for us. Some varieties are marking as intermediate days. In the mountains short day varieties work well with an early spring planting because we often have a cool transition into summer and longer daylight hours.

Onion Transplants

If you feel as though you’ve missed the window for starting onions from seed then you can always pre-order onion transplants, which skips the seed starting stage!

Written by Chris Smith

Written by Chris Smith, author of The Whole Okra, and Executive Director of The Utopian Seed Project, follow him on Instagram at @blueandyellowmakes.