Starting Onion Seeds Under a Grow Light - How many hours? - Ask Extension
When starting onion seeds indoors under a grow light, how many hours a day should the grow light be left on? I've seen some suggest 16 hours on, 8 hou...
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Starting Onion Seeds Under a Grow Light - How many hours? #781832
Asked February 14, 2022, 9:59 AM EST
When starting onion seeds indoors under a grow light, how many hours a day should the grow light be left on? I've seen some suggest 16 hours on, 8 hours off, like other vegetable seedlings. But I've seen others suggest that keeping the lights on for more than 11 hours could cause the onions to prematurely start trying to form bulbs and prevent a good crop later. I'm skeptical that the amount of light from a grow light could have this effect, given the lower intensity compared to summer sun, but this is my first time starting onions from seed, and I don't want to mess them up if I can help it. Could you clarify the ideal/acceptable hours of grow light usage for starting onion seedlings? Thanks!
Caroline County Maryland
Expert Response
We can't find specific evidence-based information to say for sure that 14-16 hours of supplemental light will cause small bulbs. The effects of light and heat on bulbing are complex. Gardeners who grow onions from seed usually treat them like their other vegetable transplants. The safest thing to do is reduce the light to 10-12 hours per day but again we don't know if this is really necessary.
An easy alternative would be winter sowing now in milk jugs. You may want to experiment. Here is more on winter sowing. Scroll down to classes and winter sowing. You will see a video and a presentation. https://extension.umd.edu/locations/washington-county/home-gardening/classes-and-events
Marian
An easy alternative would be winter sowing now in milk jugs. You may want to experiment. Here is more on winter sowing. Scroll down to classes and winter sowing. You will see a video and a presentation. https://extension.umd.edu/locations/washington-county/home-gardening/classes-and-events
Marian
