Do Plants Need Day-Night Cycle?

I plan on growing out some seedlings ( fruits or veggies) indoors this year.

I was wondering if it hurts or helps to keep the lights ON 24/7.

Would 24 hours of light make them grow more or become more robust?

Since the light we supply is not as strong as sunlight the question is how many “units” of light do they need?.

Is there a difference with more intense light for a shorter period or less intense for a longer period?

So do the plantlings need a “night/sleep” cycle to grow best.?

There I go again with my winter musings since there is nothing else to do while waiting for spring? Idle minds and all …


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My understanding is 18 hours light is optimal

From my experience, peppers and tomatoes show no advantage to more than a 12 12 cycle after first set of true leaves.

Seedlings with only cotyledons I keep lights on 24/7 which is only about a week to 10 days.

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My figs do fine with light 24/7. They fruit and grow fine.

There are plants that need various day lengths to flower. Or day length affects the switch from vegetative growth to flowering. But I think most fruit plants would be fine with 24/7 light after they set fruit.

The two years I’ve been growing toms and peppers indoors, I’ve set my timer to turn on the lights from about 8am until midnight, or 16 hours. I put the lights about 3in above the leaves, and raise them with a chain as the plants get taller. The closer you can keep the lights to the plants, the less “leggy” they get.

I also brush them occasionally or blow on them some to help them get a bit more thicker stalks. Some folks use a small fan to occasionally blow across them for this effect. I’ve considered doing that this season.

FWIW, I use 6500K fluorescent T8 lights to get the plants more bluish light, which is supposedly better for vegetative growth. I put my plants in the ground before they start to flower, but if you were keeping them the house thru that stage, it’d prob be better to have a mix of the bluish lights and the redder lights, like with 3000K bulbs.

As far as units of light needed, I don’t worry about that, I guess you’re talking about lumens? I think I have read that the closer the lights are to the leaves, the more lumens they get? I could be wrong.

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I have a T5 VHO (not HO) lights, and I don’t need plants closer than a foot. The more lumens the light throws, the farther you can keep the plant.I have 4 lamp, 4 foot long fixture, it throws out 28,800 lumens. I also have a T5 VO 4 footer, 4 lamps I like this light better, the VHO becomes way too hot.
This lamp throws out 20,000 lumens.You can buy these for around $135.00. Maybe cheaper at home depot, Lowes etc. .
My figs will grow well under these lights, and could be kept indoors all year.

I also run a fan hooked to my timer. I have to with the T5 VHO else it would burn my plants. I only keep light on about 15 hours.
I like having these larger fixtures, they work so well, I keep herbs under one for the winter. I have to have fresh basil, oregano and rosemary at all times :thumbsup:


I also have a 4 bulb 4ft fixture, but as mentioned earlier, they are T8’s. I looked into getting T5’s before I started growing stuff indoors, and thought they were way too expensive for me. I’m sure they’re more efficient, but just not worth the extra cost. Plus the bulbs are hard to find in these parts.

I can find T8’s at Lowe’s, but the 6500k bulbs are bit more rare. I got a good deal on some a couple years ago, I prob should bought more than I did. The T8 fixture was about $50 and the bulbs were about $8 for a pair at the time, if I remember correctly. They are 32W, 2800 lumen GE bulbs. They do the trick, and don’t get very warm at all.

The last couple of years I’ve grown stuff, the plants sit on a table in our hallway, and the light fixture hangs by chains from a 2x2 inch 6ft post that sits on two bookcases. Since theres no outlets in the hall, I have to run an extension cord back to the office, where its plugged into a timer. Quite a hokey set up, but it works.

Last year, it was quite crowded with all the toms and pepper seedlings I had growing. I think I had one and a half 72 pod Jiffy trays going, that’s a lot of plants, for me anyways. It got really crowded when I transferred them from the peat pods to cups.

Since I’m going to try some super hot chinensis pepper varieties this year, I’m going to have plant those seeds prob within the next month. Some of those have a 120 days from plant to harvest window, so gotta get a jump on that.

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Yes it will do the job. Only my VHO becomes warm, it looks almost like sunlight. When I get up in the morning just going out into the hall, the light from the other bedroom is blinding. Impressive output. Pot is legal here and we have hydroponic stores on every corner. they all carry T5’s. They don’t carry the VHO lamps, I have too mail order to get them. I like the power as I can put a lot of plants under the lights. Since it’s up higher it covers more area.

Any helpful hints on getting those super hot pepper seeds to germinate? They are 7 pots and chocolate habs (thanks to a member on here!). Didn’t you say you soak them in some kind of solution, or maybe stratify them, whatever that means? And, even after doing all that, do they just take longer to sprout?

We watched some YouTube videos of folks eating some of those super hots, like the 7 pots, Carolina Reapers, Trinidad Scorpions, etc. Supposedly the challenge is eat the pepper whole, and sit there for 5 minutes without any liquids or food. Talk about crazy folks, the reactions are hilarious sometimes. I like hot peppers, but don’t know if I could down one of those!


I’d say it depends on the plant. I start a lot of trees from seeds and nuts indoors. For most, I use inexpensive fluorescent shop lights rigged so they are height adjustable. These are cool so unlike the expensive grow lights they can be kept very close to my seedlings. Light energy diminishes with the distance squared, so I find I can do as well with these cheap lights. The spectrum (wavelength) doesn’t matter much for my seedlings. This may not be true for all plants as they need different wavelengths at different stages. My trees only spend a tiny fraction of their lives indoors, so for me lumens per dollar is more important than spectrum.

Most of the tree seedlings I’ve grown do best with a 15 hour day. I can’t speak to other plants, but the trees I have grown seem to do best with a rest period.


Just keep them warm 80 to 90 degrees and soil moist not wet. Soaking them in any type of mixture does not speed up germination

Do not use any nutrients in the growing medium while germinating.

This is a germination box I used to use, it was very effective and kept the temps pretty close to optimum 24/7. the light served no purpose in germinating just for viewing.


Thanks for the suggestions. I’ll be sure to keep them on the heating seedling pad.

Wow, what a setup! I suppose that’s in the basement? That’s like a pepper factory. Who is that in the second pic, it looks like a doll or something.

Is that a pimente de neyde there in the front? They are are purple pepper, are the leaves really dark as well? It’s supposed to be pretty hot from what I’ve read.

Actually its my son, these pics are a few years old. He is 10 now and really knows a lot about gardening as do my two older sons.

The Pimente de Neyde is more a ornamental and I personally find no culinary value in it. It is hot.

Another thing I do now when germinating is put paper towels over my seed trays and spray with water to keep them wet but not dripping so that in turn helps to keep the pro mix moist longer. I also put a dome over the tray.

With that setup, I’ll bet you can germinate seedless watermelons

Oh, I’m sorry, I couldn’t tell. Good to hear your boys have taken to your hobby. Although at the scale your doing it, it’s prob much more than just a hobby.

What does your pro mix consist of? I’ve read other folks say that something in peat is not too conducive for pepper germination. I think they felt that peat is too acidic for the seeds. They actually recommend Orchid Mix or Organic Choice from Miracle Gro. So I will try something other than peat for the peppers. The tom’s will be OK in the peat. I also use a dome on my trays until they start sprouting, it can get quite steamy in there.

Gardening to me has become an addiction for sure, it was easier for me to quit smoking than it would be to quit gardening. I also trade seeds from all over the world…

As far as growing medium goes in the chili head community anything peat pellet related and miracle grow related is frowned upon for seed starting. The high end soilless mixes are used by most. Whatever you use just make sure it has no nutrients. .

I forgot about this, to me this is a key, keeping high humidity around the seeds works well, that consistent moist not wet is much easier and is what really germinates the seeds with heat too.
Nice set up Dale, wow! I have to show my wife those pictures, so maybe I can ramp it up a little. See I’m not that bad kinda thing :head_bandage:

I do use the miracle seed starting. I could make my own, it’s just convenient. Another commercial seed starter product is out there, and I have never been able to germinate in it! I forget the name? If I grew more, I would need to make my own to make it more economical. I mix it with 1/3 DE. You can germinate in 100% DE, I did it once, but liked results with a mixture. The main thing about seed starter that helps, is that it is sterile, no root rot fungi, which is just about in every other soil, including potting soil. DE holds 120% of it’s weight in water. More than clays like turface.
So the mix stays moist longer. Plus it’s easier to wet dry peat when it’s mixed with DE. Forming channels for water absorption by the peat. Often water will run right off peat, DE helps pull it in. Not perfect but better. Another thing that helped me out was buying a thermostat for my heating mat. Keeping temps constant and right where we want them. This also made a major difference.
You can see the temperature probe in Dale’s photo of his germination box. What reminded me I use a thermostat. I’m getting old!

I like using the seed trays. You can buy kits with one seed tray and dome, . Another useful item are watering mats. I have one, but don’t always use it. I like them more for 2-4 week old plants that often all of a sudden suck huge amounts of water. The mat makes it somewhat self watering.

I buy most of my supplies at Greenhouse Megastore. I don’t use ton’s of equipment, prices are decent, maybe not the best, they just have everything under one roof. Including root pouches etc.

What drives me crazy are the hydrophobic mixes

I also get stuff from the megastore, I buy my 4" pots by the case.

The germination box has two waterbed heaters underneath connected to a White Rodgers remote bulb thermostat. Power going in from fuse box power going out to an electrical outlet that is only powered on as the temp drops below pre set temp and heaters plug into outlet. I would not trust the thermostats on the heaters they are very erratic but do help with fine tuning.