light schedule

[Scooter]

This may be a duplicate. I have been using an 18 hour on and 6 hour off schedule for vegging. I have read that 6 hour on and 2 hour off is preferred. Question is is 4.5 hours on and 1.5 hours off going to give me better results than 18 on and 6 off. Thanks in advance

[Spidermite]

I run a 20/4 schedule in veg. I've seen many attempt the method your referring to but never heard back on results. I have yet to see anywhere that said it was preferable or had better results. That's not to say it isnt but I just have yet to see verifiable results.

[Tersky]

I had never heard of that. I looked it up and saw some posts on some forums but no scientific evidence (granted i didnt look too hard). My personal amateur opinion is stick with 18/6 and 12/12. Try to replicate the plant's natural light cycle as much as possible. Not saying it wont work, but i know what i do works well and im not gonna mess with that. I found a reddit post about it and the top reply pretty much says what i was thinking but he has some knowledge to back it up. https://www.reddit.com/r/SpaceBucket...rk_grow_cycle/

Here is the reply from the article:

his article is so full of mistakes that my head just exploded. I'm going out to breakfast and will be back to explain why this is utter non-sense.

edit- back, hotel food sucks

FTA: There is a lot of research that suggests that cannabis plants can only process a certain amount of light per day. After that level has been reached, the plant can no longer absorb more light, and any additional light is essentially wasted. By breaking the light cycle into multiple 6 hour periods, the plant is able to rest and process the light it has received. When the lights come back on 2 hours later, the plant will be ready to process additional light, allowing you to get the most plant growth out of every minute your lights are on.

Plants have a ideal DLI level. DLI for certain plants can be found in this pdf paper. If you exceed DLI for lettuce then you can have issues such as leaf edge burn. This is an osmosis problem in the leaf which can be partially corrected by boosting calcium levels. The link provided is also dead.

At a biological level, cannabis’s inability to grow more once it has received a certain amount of light can be attributed to the way the plant processes carbon dioxide (CO2). A majority of the mass accumulated in cannabis is associated with the amount of CO2 found inside plant cells. While under light, cannabis tries to prevent CO2 from leaving its cells by cutting off transpiration. However, this prevents new CO2 from entering into the cell, blocking new growth. When the lights are turned off, and no photosynthesis is occurring, the plant is able to absorb new CO2 into its cells.

The link is only to an abstract that deals with PPFD which is instantaneous lighting levels. It is only at very high CO2 levels that stomata starts to close. A build up of excess sucrose, which is a photosynthate product, can signal the Calvin cycle to slow down (the 3 carbon sugars are converted to other sugars such as sucrose). Furthermore, the sugars can be converted to starches which can physically block sugar flow and damage chloroplasts which contain chlorophyll.

If the plant has a large sugar sink such as potato or radish plants then this sucrose/carbohydrate build up tends not to occur in the leaves. The above is explained in this pdf paper.

Also, when the lights are off the stomata are closed so there is no gas exchange like CO2 uptake.

Additionally, when plants are exposed to 18 straight hours of intense light, they become stressed. Signs of stress - droopy or curled leaves - will usually appear towards the end of the light cycle. While some stress can be beneficial to plant growth, too much stress can cause harm to your plants and prevent them from reaching maximum growth potential.

Any high lighting levels can cause leaf cupping. Cupping is a hormonal imbalance in a leaf and the idea that it happens at the end of a light cycle is unfounded. Droopy leaves are a sign that a plant does not have enough water and has to do with turgor pressure.

Giving plants 6 hours of intense light at a time not only puts less stress on the plants, it also spread out the load on your cooling system over a longer period of time. The cooling system works the hardest when lights are on. By turning off the lights for 2 hours at a time throughout the day, your cooling system will get a break between light cycles, allowing the room to be cooled to desired temperatures before the lights come back on. With a properly sized cooling system, this benefit will be minimized as the system will be designed to handle the heat load throughout the entire light cycle.

This is just straight up not understanding how plants work. Plants have three cooling methods: there is transpiration, there is NPQ where the xanthophyll cycle plays a role, and plant leaves have an emissivity of around 0.95 so are good at removing heat through long wave IR radiation.

Plants do not need a cooling break and have not evolved that way. The xanthopyll cycle likely evolved so no break is needed.

While there are many approaches to Veg light cycles for cannabis, a 6/2 schedule allows for maximum plant growth. A 6/2 schedule allows plants to process more intense light, prevents plants from becoming stressed and puts less stress on your cooling system. It’s a win all around. Give your plants a break every 2 hours and you’ll be amazed at the results.

This is all speculation from a misunderstanding how plants work.

This is my issues with bloggers who do not actually understand botany yet put out information like this. It perpetuates these sort of urban legends.

[Spidermite]

I can tell you one thing for a fact and that is that I can tell when the lights turn off because the plants immediately release a different odor. Try growing 2 big plants in a tent in your bedroom without a carbon filter and you will see the same thing. I have no idea what that means but it is real.

I am not one for using big words but I love reading everything I can find on growing plants. I'm halfway through my Masters Gardner program with the state.

My 20/4 schedule is just from experience. It works for me. Anyone who knows me would not argue that what I do works for me. If you can afford the time, plants, and occasionally completely failing try new stuff and see of it works. But first get your base growing skills honed in. 18/6 is the best all around schedule for veg. If you have time and space play around with it. Otherwise stick to the basics that have worked since the earth was formed.

[kingfish]

For 10 years a 18/6 for vegging and 12/12 for flowering has worked for me and I'm to old and set in my ways to change now. I mean no disrespect.

[Spidermite]

You could never disrespect a person for growing the way you grow. I accept all good growers. I have a very hard time giving advice because there are so many good growers. I dont think we have 2 that do everything the same. I only know what works for me.

[sgiacomo]

Using 18/6 and 12/12 here. On my third grow, first two were great!

[Spidermite]

Use what works. If it works for you then keep up with it.

[Spidermite]

Ok I feel I need to say that I have lots of plants, lots of setups, been growing my whole life, and I like to push the envelope and test new things. Never take what I say as fact it's just what I've done and what worked for me. I have failures a plenty and have posted many of them. I just happen to have lots of land. Over 8 full indoor setups, and love to try stuff. 18/6 is where I would start anyone who is fairly new.

Just felt I should say that.

[starramus]

This may be a duplicate. I have been using an 18 hour on and 6 hour off schedule for vegging. I have read that 6 hour on and 2 hour off is preferred. Question is is 4.5 hours on and 1.5 hours off going to give me better results than 18 on and 6 off. Thanks in advance

I'd stick with the 18/6. 4.5 on, and 1.5 off seems would be the light schedule for a plant that evolved on an entirely different planet! Maybe that extra solar planet Pegasi 51.

[Scooter]

To all whom have commented. Thank you. I am sticking with 18/6. I have also read the same info as you have posted. Hence the reason for the question. I have done 3 grows inside on my fourth. Where I am at I only vegg inside and move the plants outside for flower works great. Again Thank You for the input great forum.