Too Much Light Harmful for Seedlings?

I have read that seedlings under artificial light should receive 16-18 hrs of light each 24 hrs. Is there a down side to providing them continuous light and not trying to create an artificial day/night cycle?

Wasn't for me with over 100 tomato and pepper seedlings. Had them under one 4 bulb 48" fixture and one 2 bulb 48" fixture. Mostly I left both fixtures on. Now and then, for no particular reason or at any particular time, I turned the big fixture off for a few hours (maybe 12 hours total a week at most). Think I never or almost never turned off the 2 bulber.

But the real answer is "I don't know". Worked for me. Once. We'll see this year.

I don't know either--it may vary depending on what you're growing. But 24 hrs of light isn't going to be any better for the seedlings than 16 hrs, and you'll save on electricity if you don't leave them on constantly.

I've always gone the 14-16 hours of light route with my lights, I've read that the plants need some time in the dark. But occasionally I've forgotten to turn off the lights for a night or two with no ill effects, so I don't know if it would have harmed the seedlings if the lights had been left on. But as previously stated, why spend extra money on electricity and wear out the lights when it's not necessary. I now have all my lights on timers so there's no remembering to turn on and off.

I keep my lights on 24/7 for the germinating seedlings and babies only. I want them to see the light of day as soon as they germinate so they are stocky. The downside is the expense. Apparently not noticeable on the electric bill, or I'd have heard about it from the bill payer around here, but still wasteful.

My young veggie plants got very stressed under 24 hours of light, they yellowed and stopped growing. Once I switched to a 16/6 plan the ones that didn't die had fresh dark green growth and they perked right up.

They were ok as seedlings, but once their true leaves came in the constant light just made them sick. I bought a cheap timer from Lowes and that solved the problem. Apparently the plants need a dark peroid to do the actual growing or something. I don't quite remember. I just know if I was awake 24 hours a day, I'd die of stress pretty quick too, lol.

once my seeds germinate i put them under grow lights for 16 to 17 hours a day have them set on timer. they go on when the sun comes up and turn off when the sun goes down.

You know I was reading all this last night and had a eureka moment.
It would just stand to reason they don't need light 24 hours a day after they germinate, they don't get it naturally. Boiiing!!!

lorraine - just think of what plants go through after you plant them outside. they get sunlight from about 6 a.m. until almost
9 p.m. which is about 15 hours.

I thank everyone for the thoughtful responses.

The reason I asked the question is that I have a unique situation: I have my seed-starting operation in my unheated garage, the "hardware" essentially being heavy duty shelving with four fluorescent bulbs on the underside of three of the four shelves. I have covered all four sides with plastic sheeting to retain warmth. Because it's still very much winter here, I must leave at least some of the bulbs on at all times to provide enough heat. The usual temperature in the garage is 30-40 degrees with occasional blasts of 15-20 degrees when the doors are up.

I have tried the recommended cycling but sometimes the ballasts don't work very well in the cold (they are rated for only 50 degrees or more) so I don't have dependable re-ignition.

So I will forced to provide light 24/7, at least until the weather warms a little. I will view this as an experiment and post my findings in the future. Hopefully my experience will be like David_Paul's. Stay tuned.

Naw, they'll be fine -- I kept them on last year 24/7 the whole pre-spring season and everything grew great.

It's just that this year I have them on a timer.

Suzy

Goner...that's a creative way to handle the problem. I use lights for heat too but for seed starting. Spend a little more and got Park's stainless steel 4 bulb 48" fixture. The flat top makes a great heating pad....sometimes too much so....have to watch it doesn't overheat the trays. Putting a towel between the fixture and the tray makes it a little easier to monitor though.

Goner,

Since you are working in an unheated area, are you using heatmats as well? Using them may mean that you don't need the lights as much for heat.

When do you all take the plants out from under the lights and just put them in natural sunlight, you know, close to windows and stuff

Oh, Lorraine, you and your fellow Texans are always so cute! I don't have sun up here in winter, and with the heat on, it's too hot to grow things in a window -- the seedlings get too leggy. My seedlings go from under lights to outside, but the temperatures have to be at least as warm as inside, and with the future looking pretty good, too. It is an onerous chore because they have to be hardened of....this means moving everything out for a couple hours for 3 days in a row, for longer periods of time each time. Then taking a chance andleaving them out all day for a couple days, and then overnight. Do youuderstand the work involved in moving up and then back down every single seedling pot? I use cafeteria trays, but even so, we have chicken fingers for dinner because i am so tired LOL!

This usually means March 28th for perennials and cold-hardy annuals, and middle of April, with an eye to the weather channel at all times, for the more tender stuff. We can have gusher rainfall, and that has to be thought out, too.

Because of the timing and all the work that happens in a relatively short time, I broke down and bought a plastic greenhouse (plastic clear bubble structure -- colder than heck in there when the sun isn't shining.

I keep looking at all these little and big containers thinking ":have I lost my stinkin' mind?

mine never see natural daylight untiol i start to harden them off a week before june first.

Thanks Illoqun, never been called "cute Texan" before. Well, when I lived in California people would talk to me just to hear me talk. I was at work one day and had this guy call for a second time. He told me he didn't really need anything, but he was from Texas and just wanted to hear me talk. ha ha.
I don't have a southern accent, I have a twang, and no, I can't ride a horse, do have a cowboy hat and boots, but do have a gun.!!

Goner,

Since you need to keep the lights on 24-7 to provide the heat for germination, have your setup covered in plastic sheeting for warmth, and are worried about the seedlings getting too much light, couldn't you just throw a black plastic garbage bag over your setup at night and take it off in the morning?

That way, you would limit the light the seedlings get, and keep in the heat (you may even get a little more as the black garbage bag would absorb the heat of the lights..)



This message was edited Mar 11, 2009 1:41 PM

This message was edited Mar 11, 2009 1:43 PM