Effect of 24 hour lights on seedlings

[ScottinAtlanta]

Folks, I am getting ready for my annual tomato sale here in Atlanta, and about 20% of my seedlings are much smaller than the others, for whatever reason. I have hit them with a diluted fish fert to speed them up.

Does it speed up the growth of seedlings to keep them under T5 lights for 24 hours a day? Or should I switch off the lights at night to accommodate their natural schedule?

[jmsieglaff]

I cannot speak to your light question, so I will be brief. I have found temperature seems to make the biggest difference assuming normal light conditions. Do you have a sheltered location outside they could be in the warmth of the sun and brought in at night if it's cold?

[PaulF]

Here is what I have always thought: Tomatoes need a light and a dark time for optimum healthy growth. My plants get a 16 hour lights on, 8 hours off.

Here is what I have recently researched: Most sources say plants need light and dark time to mimic natural light/dark schedules but then do not give a reason why or what happens.

The more scientific sources explain that natural sunlight has many more photons per hour so that the light requirements for photosynthesis is met after 5 or 6 hours. This energy is stored and is converted into carbohydrates during the dark cycle. Plants, and particularly fruiting plants...tomatoes...need a light/dark cycle.

Seedlings grown indoors need a certain amount of photons to mimic the natural cycle. Using artificial light sources the photon level for proper photosynthesis/ carbohydrate production for plant growth depends on the light source used. With fluorescent lights (mine being shop lights, full spectrum) the ratio to light and dark timing is optimum at 16 hours on and 8 hours off. More intense lights will require less light. As the plants get larger, less light is needed for proper growth. For twenty-five years I have just kept the timers at 16/8 rather than reset the ratio. Works for me.

[AKmark]

Originally Posted by PaulF

Here is what I have always thought: Tomatoes need a light and a dark time for optimum healthy growth. My plants get a 16 hour lights on, 8 hours off.

Here is what I have recently researched: Most sources say plants need light and dark time to mimic natural light/dark schedules but then do not give a reason why or what happens.

The more scientific sources explain that natural sunlight has many more photons per hour so that the light requirements for photosynthesis is met after 5 or 6 hours. This energy is stored and is converted into carbohydrates during the dark cycle. Plants, and particularly fruiting plants...tomatoes...need a light/dark cycle.

Seedlings grown indoors need a certain amount of photons to mimic the natural cycle. Using artificial light sources the photon level for proper photosynthesis/ carbohydrate production for plant growth depends on the light source used. With fluorescent lights (mine being shop lights, full spectrum) the ratio to light and dark timing is optimum at 16 hours on and 8 hours off. More intense lights will require less light. As the plants get larger, less light is needed for proper growth. For twenty-five years I have just kept the timers at 16/8 rather than reset the ratio. Works for me.

Hmmm, I have found different results. I start loads under lights, 30-50k, we also barely get nightime up here in the Summer. I have often just let the lights run to keep the starter room very warm so we can sprout seedlings in a few days, as they sprout and get a real set of leaves, we then remove them to a GH.

[ScottinAtlanta]

Thanks, folks. I am now running them on a 20 4 schedule to try to speed them up. I don't want to get stuck with a bunch of seedlings that take off 3 days too late!

[kurt]

https://www.google.com/search?q=why+...e-gws-wiz-serp

Some interesting facts.This is why they used to take out flowers at night in hospital rooms,back then

[brownrexx]

I had always heard, but didn't research, that tomatoes need a period of darkness for best growth. I have noticed that mine seem to germinate and also to grow at night. Mine just put out their first leaves and I noticed that it happened overnight so I am sticking to a period of darkness.

Maybe you could keep the soil warmer if you want to speed up growth. Tomatoes love heat.

[Gardeneer]

In my opinion it is better to copy the nature. Just an opinion.
As some you just said, plants germinate and grow perhaps more during dark time.
I see this in my garden when I sow seed. During the day they stop poppig.
I think plants do not grow just because of light. Actually they grow faster in the shade and with less light.

[Milan HP]

I am no expert, but I agree with Gardeneer. My reasoning goes like: throughout the billions of years of evolution, plants have adjusted to what they get from Mother Nature. And there's never been a 24-hour day. They most probably need the night as much as the day. Well, we can change the length artificially, but it's just like moving them south or north respectively (or giving them a different season). Tomatoes come from Mexico and the day in winter there is shorter than 12 hours. However, the light is much more intensive and the temperatures are higher, too.
So, my suggested solution to your problem is: raise the intensity of light and raise the temps mainly of soil (heating mat?). And make sure the root system gets some oxygen. I don't think any extra nutrients will help much, neither will more water. The ability of the root system to absorb either is limited. There's a danger though: they can "overdo" it and grow too fast. Which will result in leggy seedlings.

In terms of day/night ratio, you probably won't get any benefit from anything higher than 16/8. I suspect going to 14/10 (or even a bit less) could bring the same results.

Milan HP

[rhoder551]

Can you put them outside in the sun? Most of mine were dinky and growing really slooooow under lights. Then the weather warmed and I put them outside in the sun and they shot up. I had them under lights about 16 hours a day. And I did give them diluted maxsea fertilizer every time I watered but the sun seemed to make a big difference. It was a giant pain moving them out then inside again at night but I did notice an increase in growth..

[swordy]

The first month I kept moving the seedings tray from window to heater and backwards. Now I take them out during the day and bring them in for the night. I also noticed that during night seeds sprout and more noticeable growth is observed. Maybe though because during the day I look at them more often, while night is about 8 hours I don't watch them..
I agree with the above that it may be best to simulate natural circles of light and dark

[jmsieglaff]

Seeing any noticeable difference in growth rate on your 20/4 light schedule Scott?

[AKmark]

Originally Posted by swordy

The first month I kept moving the seedings tray from window to heater and backwards. Now I take them out during the day and bring them in for the night. I also noticed that during night seeds sprout and more noticeable growth is observed. Maybe though because during the day I look at them more often, while night is about 8 hours I don't watch them..
I agree with the above that it may be best to simulate natural circles of light and dark

I really don't think it hurts anything. We don't really get dark in the Summer up here, a bit North it does not get dark and people have great results. Browse the thread.

http://www.tomatoville.com/showthrea...ghlight=alaska

[ScottinAtlanta]

Originally Posted by jmsieglaff

Seeing any noticeable difference in growth rate on your 20/4 light schedule Scott?

No, but they did grow really fast after I hit them with some fish fert!

[jmsieglaff]

Originally Posted by ScottinAtlanta

No, but they did grow really fast after I hit them with some fish fert!