So I've been experimenting for the last few months with hydroponics, the general goal is to have an entirely automated system. For the most part I have this in place but I'm not too happy with the results and I'm trying to eliminate potential cause for not great growth.

So I'm in Ireland, and during the summer we only really get about 6 hours of darkness at night time, and during this time, both a bit before and after, my grow light is on. Essentially my plants are getting light 24 hours a day. Now things are growing, but not as fast as they should. I have done research on nutrients and I'm monitoring on that side, but I'm wondering if perhaps the plants need a nighttime cycle? Am I over doing it by the plants essentially getting 24 hours of light everyday?


It depends on what kind of plants you have, but most plants are used to having a night time period. Exceptions are some plants growing in arctic regions.

I think for cultivation under lamps, mostly 16 hours light is used for growing phase, and 12 h light to get them in blooming/flowering period (at least this is what hemp home growers do).

  • 3
    I can confirm b.nota assertion that most plants need a dark cycle. Year's ago I read some studies that concluded that most vegetable garden plants really only perform photosynthesis for 14-16 hours, and spend the rest of the day just performing respiration. You could extrapolate this to the majority of plants safely. In conclusion, IMHO, you're wasting electricity and you are stressing the plants. Though stressing the plant's under some conditions to get certain results isn't warranted, but under most conditions, you might want to relax your light protocol a little.
    – CloneZero
    Aug 8 '17 at 15:39

I agree with CloneZero. All plants have evolved on this same planet that has specific night and day cycles...even in the arctic. Plants need darkness and a break from the work of photosynthesis. What plants are you growing? Do you know about daylight length and how that affects production of fruit/reproductive growth?

Again, what are you growing? Leafy vegetables? Ornamental foliage? Flowers and fruits? Knowing about daylight length (and strength, arctic light might as well be night) is powerful knowledge to have to grow under artificial lighting. What lamps ARE you using? How long have you been doing hydroponics? Did you ever learn gardening in the soil? What about aeration/fans/CO2...something you definitely should know with any indoor or greenhouse application.

I'd go no more than 18 hours of light per day, the rest darkness. With fans going 24/7. That will work for lettuce and ornamental foliage. To get your plants into reproductive growth for flowers and fruit you make it 12/12; 12 hours of light and 12 hours darkness. Plants should be on 18/6 at the beginning to get a nice body of vigorous photosynthetic growth going and depending on the plant, you put it into 12/12 to make it start flowering. You have to know how to do manual pollination as well. Depending on what it is you are growing.

This causes plants to start putting energy into making seed. You do have to have full control by using black plastic screens so no light even incandescent light is able to disrupt this process. You can use GREEN light to see by, however.

Plants need to 'reset' just as much as we animals do. We all evolved under the same environmental conditions with latitude, or above sea level heights and longitude constraints. No way is any plant ever going to be more productive with more light and no darkness.

Water, air, fertilizer (not 'nutrients') are critical to know and understand to be successful. Send pictures! Explain your system in detail. More about your lights...

  • Some plants in the Arctics have adapted to the long daylight summers. These traits (genes) are sometimes used by plant breeders for new plant varieties. This is why I did mention the Arctics. In the Netherlands for instance we have a lot of hemp home growing, and since some time they came up with autoflowering plants. This autoflowering trait was taken from Siberian sister species. This new plant variety doesn't react on daylight length but begins to flower immediately.
    – benn
    Aug 9 '17 at 8:10
  • @b.nota This is my new NEWS of this day. You are saying that they GMO'ed the hemp with these 24/7 plants with light and that is how they are able to kick a plant into reproductive growth immediately? Huh. I have to look this up. The pot growing has been one of the best things for plant study. Lots of minds involved in understanding just one plant. Interesting twist. Making gardeners out of us big time...Jorge Cervantes has an amazing book out about this plant that is so detailed and clearly written; "The Cannibis Encyclopedia'...excellent information for growing all plants!
    – stormy
    Aug 9 '17 at 23:00
  • Is this like 'Ruderalis'? What I've heard which is very little is that this plant in particular has a 'set' timer for it to go into reproductive mode. I hesitate to go with too young of plants made to go reproductive too soon. I guess that info is from Jorge. The detail in his encyclopedia is brilliant. Very very very little do I disagree about and that is saying something...grins.
    – stormy
    Aug 9 '17 at 23:06
  • As I understood it was not with GMO but with just the traditional way (old school plant breeding), with ruderalis indeed! I agree that knowledge from pot growing has also benefits for other crops!
    – benn
    Aug 10 '17 at 7:47
  • Thank goodness. GMO is flat out stupid as well as dangerous. The fact that companies don't have to label now is worrisome but when a company does label NON GMO, I am their customer. If it has no label I don't buy it. Even animal food. If you are looking for a great addition to your garden book library, Jorge Cervantes 'The Cannabis Encyclopedia' is mind boggling great! GMO Cannabis is hopefully not going to happen but...there was someone who did genetically enhance the THC about 20 years ago. That strain when used in combination with opiods is a killer. It reacts with the opiods...
    – stormy
    Aug 10 '17 at 19:07

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