Long Day vs. Short Day Onions

Last fall, I decided to try growing onions from seed. I figured I’d plant some seed in the fall and onion sets (baby onion plants) in the late winter. All excited, I ordered a couple packets of onion seed. When they arrived, I noticed the packets stated they were long-day onions. Curious, I researched onions online – and found out I bought the wrong type of onion seed for my latitude.

Unlike most plants, which are labeled with proper hardiness zone, onions are labeled by the amount of daylight hours needed to bulb. Short-day onions, like Vidalias, need 10-12 hour days to trigger bulbing. Long-day onions, like the Spanish onion, need 14-16 hour days.

If you live up north (Zones 1-6), you should grow long-day onions. The great number of short, winter days will give your onions lots of top growth before bulbing. This will help the plant grow large bulbs. The onions will be hard, have a pungent flavor, and store well. If you were to plant short-day onions, the plants would bulb early and be very small.

If you live in the south (Zones 7-10), as I do, you should grow short-day onions. We have less variation in day length between seasons here. (I always tell my family in New England that we have only two seasons here: summer and not-summer.) The onions will have a high water content and won’t store well. So, here, we have to refrigerate them or pickle them. If I would have planted those long-day onion seeds, they wouldn’t have received enough day length to trigger bulbing.

Intermediate (or day-neutral) onions, will grow well in Zones 5-6.

The time for sowing onion seed is past, but you can use this information for next fall. Onion sets can be planted now in the South, mid-April in the North. Your local garden center will be sure to have the proper onion sets for your area.

Today, I planted white Texas Granex onion sets in the bed with my almost-ready-to harvest Red Creole onions.

Texas Granex onion sets

Texas Granex onion sets

Now my only question is: what do I do with those long-day onion seeds?

6 comments on “Long Day vs. Short Day Onions

  1. Plant your long day seed and use them as green onions. That is what I do. One thing you defiantly got wrong is the garden centers knowing which onion set or seed to stock. They always have a mix of long and short day, and don’t know the difference.Very seldom have I met a garden center employ that knew much about the plants or seed being sold.

    • Hmmm…you’re probably right about garden center employees – at least at the “box stores.” I would bet specialty nurseries would have more knowledgeable employees. Personally, I get almost all of my seed via online seed companies like Baker Creek, Seed Savers, and Southern Exposure Seed Exchange.

      Good idea regarding the long day onions down south. Green onions are good, too!

  2. Thanks for the info! I just bought long day onions from a local plant nursery, but I live in FL. I didn’t think to look into it beforehand since the store was local. I planted them yesterday, do you think they’ll still grow enough to enjoy them? Thanks in advance for your help! 😊

    • Hi, Katy. Don’t feel bad. I originally bought long-day onion seeds for Charleston, SC when I first started my garden. Thankfully, I didn’t spend much, so I just bought the correct seeds after I discovered my error.

      As for planting long-day onions in Florida, I’m not sure what will happen. I’m sure they’ll grow. Whether or not they’ll mature properly is probably the issue. Not to mention that you don’t get a cold enough winter for those types of onions. Worst case scenario, you’ll have lots of green onions (the tops) to use in cooking! 🙂

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