When you grow cannabis indoor, it is considered beneficial, to have lights turned on up to 24h / day, during the "grow" phase. While this would prevent blooming, it is beneficial for building plant material.

When you grow spices and herbs, such as rosmary, savory, thymian, parsley etc., wouldn't it be beneficial to have the lights on 24h / day? Or do they need some dark time?

I have them in a room, which receives some indirect sun light. In addition, I have some grow lights on top of them, which are on for about 14h per day, during the day.

My idea is, to increase the lighting time to 24h / day and make use of the much cheaper night electricity price by either artificially lighting only during the night or artificially lighting 24h.

Would this be a good idea or do herbs and spices definitely need dark time?

  • I am so glad you asked this question. This is a very bad 'myth' this 'more light time is best' gig. Uh Uh. The light they get has to be in the right frequency. The proper frequency (blue light versus red light) and intensity for 'daylight' hours is critical. There is no benefit to longer hours with poor light.
    – stormy
    May 11, 2019 at 20:26

1 Answer 1


Sorry, 24 hrs/day is TOO MUCH. You start out with 18/6 vegetative growth using BLUE LIGHT. When it is time to push the reproductive growth you switch to RED LIGHT and 12/12. Religious 12/12. No light peeks in while in this phase.

PH needs to be very neutral, real close to 7 or a bit above.

Fertilizer has to be low in nitrogen. Lower in respect to Phosphorous and Potassium or you won't get much bud.

All plants have been evolved with day and night cycles. NEVER 24/7 light. Photosynthetic factories need to 'reset' at night.

The BEST book and information is in Jorge Cervantes' Cannabis Encyclopedia! I use this for ALL plants. Cannabis is creating gardeners! The detail in this book is priceless if you are growing!!

Another tip: I purchased Spider Mite Predators this year. WOW. Pull up a chair and watch these guys decimate the Spider mite population AND eggs. It is like watching Game of Thrones in battle!

Another tip: Keep those fans blowing 24/7!

Another tip: Keep your smoking friends away from your plants. All plants. Tobacco Mosaic Virus is a big big deal for marijuana and Solanaceae or the tomato family; tomatoes, eggplant, potatoes, peppers. That virus is on their hands and their breath! If they want to visit your grow room or green house or garden, have them wash their hands thoroughly with soap, put a surgical mask on them. That should impress them! Grins! Get that book NOW. You will be humbled and taught how to grow anything properly. Jorge Cervantes Cannabis Encyclopedia

  • Thanks but I think you might have misunderstood. I come from a cannabis background trying to grow actual spices and herbs for cooking lol. May 11, 2019 at 21:04
  • That is what I assumed, yes. Cannabis does NOT do well, no plant does well much less 'better' with 24/7 light. Herbs and spices and Cannabis need pretty much the same resources. This one book will help you grow Cannabis correctly, at the same time teach you how to grow all plants correctly using the basics. Your question asked do plants do better with longer light hours. I want to make it clear, no plant does better with more light for more hours per day. I tried to connect with what you know to help shed some light (grins) on your question; for Cannabis AND Herbs and all other plants.
    – stormy
    May 13, 2019 at 4:11
  • And dark time has nothing to do with development of 'Nutrients' and 'flavor'. Plants do not need any kind of nutrient. They make their own food ONLY if there is just enough of the right chemistry those photosynthetic factories HAVE to have to do photosynthesis to make carbohydrates for the plants as well as us humans. Correct intensity, stability of hours, routines with turning and turning off the lights, careful watering, just enough fertilizer and air blowing on any plant growing indoors. Your hair should move in the breeze!
    – stormy
    May 13, 2019 at 4:15
  • Thx, that's very helpful May 13, 2019 at 5:17
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    For light time, like everything else, you cannot really cheat with natural cycles. As stormy stated it, you should absolutely avoid a 24 hour exposition
    – imrok
    Jun 10, 2019 at 21:39

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