don't know where you got this idea! i'd throw that book out or stop reading at that website because they are wrong - dead wrong.

all plants under shop lights require 16 hours of light and 8 hours of dark. period.

if you did have to start over AND YOU DO NOT it is too late. onions have to be started about 8 weeks before setting out so it is too late to start new seed this late.

bulbing in the north above 40 degrees occurs as the days attain their longest day or by the shortest night. to be honest i'm not sure but i think it is the 15 hours of day light not the 9 hours of dark. but whichever, that is what triggers bulb formation

below 28 degrees north the same occurs but it is the 13 hour day.

this is why you can't grow day long onions down south and you can't grow day short onions up north - they don't bulb properly. day neutral onions will bulb properly at any latitude.

you'd better read up on fertilizing (very very little required), watering (1" per week), weeding (they do not tolerate weeds), when to push them over at the neck and how, harvest and curing. if you got this lousy info on light, you certainly need to educate yourself asap.

tom

tjg911, thanks for the info, you sound quite certain, but I'm always running into completely opposite opinions and advice. You didn't say whether you'd actually grown onions from seed?

I do believe bulbing can be triggered in onion seedlings, I'm just not sure of whether fluorescents will do it at 14-16 hrs. So I wonder when I read stuff like this:

"If you start onion seeds under lights, remember to turn the grow lights off to give the plants a suitable night. Onion seedlings will bulb too early if exposed to long days at any time during their development. You will not get anything bigger than sets." - Jarvis, B., Yard & Garden Line News, University of Minnesota Cooperative Extension, Volume 3 Number 2, February 1, 2001

I'm a small scale market gardener, so I'm quite familiar with wildly differing growing advice, and how it all compares to first-hand experience. I grow about 1,500 lbs of yellow cooking onions from sets, so I know about culture, except for seed starting. This is my first year growing onion from seed, so I guess I'll find out for myself about the lights in a few months!

You didn't say whether you'd actually grown onions from seed?

yes, i grow 3 varieties each year from seeds. i used to buy plants and forget sets all together. i've grown onions from seeds for several seasons under shop lights so i do know what i am talking about. you are wise to question my experience as i'm telling you flat out that advice is pure bs. a lot of people on the net like to give advice. i doubt they mean to be misleading but sometimes they are just that.

I do believe bulbing can be triggered in onion seedlings, I'm just not sure of whether fluorescents will do it at 14-16 hrs. So I wonder when I read stuff like this:

"If you start onion seeds under lights, remember to turn the grow lights off to give the plants a suitable night. Onion seedlings will bulb too early if exposed to long days at any time during their development. You will not get anything bigger than sets." - Jarvis, B., Yard & Garden Line News, University of Minnesota Cooperative Extension, Volume 3 Number 2, February 1, 2001/

i agree that all plants need that dark time to rest. it occurs in nature. but plants under shop lights require 16 hours of light followed by 8 hours of dark. now i'm going to make a swag, remember i told you that the longest days or shortest nights trigger bulb formation. so perhaps, just a swag now, if you vary the length of the light the plants are exposed to, increasing it from say 8 to 16 hours over a few weeks time THEN possibly you fooled the plants into thinking they went from april to mid june and that is exactly the scenerio that causes bulbing IN NATURE. i know of no one that does this with shop lights. no one. start with 16 on, 8 off, until you've hardened them off and plant them outside. going from 16 hours of shop light to say 14 hours of natural sun light DOES NOT effect the plants and cause them to start bulbing. believe me all i have written is true! oh, btw, where i live the longest day is 15 hours and my giving the plants 16 hours of shop light light does not effect the plants when they go out in late april with a 14.5 hour day. if you gave the plants 24 hours of light that would harm them as they need a dark period to rest.

i grow about 33 to 40 pounds of each variety each year, my methods work just fine. good luck.

tom

Hey, I realize this thread is roughly 2 years old but I keep running acrossed it so I guess it's still being looked at. I know that more then 12 hours of fluorescent light a day is ok. Last year I kept mine at 12 hours a day from Jan.15th to March15th and they were still only a little bigger than toothpick size when I transplanted them to the garden (Most pages say they should be pencil size for transplants). Then I got "Guide to Virginia Vegetable Gardening" and on page 44 I noticed that it said to leave the fluorescent lights on for 18 hours a day. It wasn't specific to onions so I searched online again and found that 18 hours for onions were kinda common. Then I ran acrossed a webpage (Link below, scroll down to where it says artificial lighting) where a guy grows competition onions and he leaves the lights on for 24 hours a day for the first 6 weeks and then starts to cut back to till he's at 12 hours a day. Aight, Good Luck!

Here is a link that might be useful: Growing onions

Right, a 14 year old thread but full of nonsense which needs corrected for the next person with the same curious question.

Photoperiodism in Onions with no exception to any cultivar will not respond until the plant has it's fourth leaf. The first single leaf with the seed shell on it's tip doesn't count and is the onions cotyledon leaf.

This would be why the article Seduvsten quoted concerning competition onions can be classified as truth but the grower knows when to cut the light. He also grew onions for 3 months with 12 hours of light and only the size of a toothpick, and with certainty it was the result of a lack of fertilizer and nothing to do with the length of light, 12 hours is plenty.

The quote stating "plants need 16 hours light 8 hours dark, period" is not true at all. The luminous intensity of light means more than length so with the correct intensity seedlings will grow just fine with 10 to 12 hours under the lights.

@tbronson had a very good question and deserved a good answer but didn't get one. Yes, onions under 15-16 hr lights may cause an onion to respond to change but only if they have 4 leaves or more. Temperature, nutrition, environment and light intensity will alter the length of light required to respond, for long day it's 14 to 16 hrs of light and short day it's 10 to 12 hours so there is no absolute time, just a window which can vary based on conditions.

All plants grown under shop lights necessitate 16 hours of light and 8 hours of darkness. Onions must be started about 8 weeks before planting, so it is too late to start a new seed at this point. You should educate yourself on fertilizing (very little is required), watering (1" per week), weeding (they do not tolerate weeds), when and how to push them over at the neck, harvesting, and curing. If you got this crappy information on light, you should definitely educate yourself as soon as possible.