Cannabis matures by about day 21 to be able to process 1kµmol of light. That's in ambient CO2.
In my current grow, it took a while longer because I topped above the fourth node at day 17 and held PPFD constant for a few days.
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The statement about "catch up" is part of the paragraph that starts with "it[sic] putting more light on your plants." Increasing light levels later in the grow cannot make up for low light levels at the start of the grow in terms of putting more light on plants. The most easily quantifiable aspect is yield.
Yield is a function of how many photons a plant has received over the course of the grow. The reason for that is that light is the only way that plants can make food. As long as light is the limiting factor and as long as all other conditions are the same and as long as the plant does not receive light above its light saturation point, the plant that receives more light will tend to yield more than a plant that receives less light.
With autoflowers, it's especially important because, like it or not, that plant's gonna go into flower when it wants to (most of the time!). By about day 21, autoflowers start to change internally to get ready to go into flower. That means that it's a real rush to get as much light onto the plant to build out the canopy as much as possible.
It depends on what your goals are, of course. Cannabis will survive at about 100 µmol or higher so you can make the argument that there's no need for more than X PPFD but that's where the word "need" derails the conversation. Instead of trying to wrestle down what the word "need" means, it's a lot easier to discuss how cannabis responds to different parts of the grow environment and let the grower make the decision about how to get the outcome they want. If a grower wants to grow at 300 µmol because they've decided that's what their plant "needs", no argument from me!
My goals are to maximize crop yield, crop quality, and bud quality and every piece of information I've seen in the past four years indicates that the way to do that is to get as much light as you can on your plants as early as possible (normal caveats). That will help ensure that the canopy is as large as possible in veg so that the canopy can capture the maximum amount of light in the reproductive stage.
When growing autos, that's about right. Cannabis is a light whore. Along with corn and sugar cane, cannabis is the most light hungry crop we have.
Once I hit 1k, that's pretty much where I leave the lights. It's very hard to get consistent measurements. By mid veg, I sample 9 points and, when colas are well above the canopy, I just track the PPFD hitting the buds.
From yesterday. Total wattage (Growcraft X3 flower light + Spider GlowR80's) was 344. PPFD's for 9 spots on the canopy, row and column averages and standard deviations. The SD's indicate that the front and back rows are even but the average shows that the back row is a bit low.
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Sometimes I've dropped my autos to 20/4 or 21/3. As I wrote in my grow journal a few years ago, paraphrasing, "there's so much weed in there that why bother?". Other than that, though, I keep my light levels high because that's how I get the outcome that I want.
Ambient CO2.
I picked up on that.
I was very skeptical, as well.
I've been growing cannabis for four years now at least two crops a year and thought I was pushing my plants by getting them to 1000µmol by day 35. That was wrong.
In fact, the reason it was taking
so long to get my plants to 1000µmol was because I wasn't giving them enough fertilizer. It really was that simple.
After I spent about a week uploading photos and examining my previous grows and my grow processes with ChatGPT that I got excellent feedback in a few areas. GPT is very able in terms of "discussing" an issue and, since it has access to such a vast amount of information, it is able to substantiate its arguments and conclusions by citing sources.
Of course, it has made mistakes and it can be frustrating to communicate with GPT. Yesterday, I wanted it to model the PPFD values that would result from using a pair of lights designed for a 2' tent when they were hung in a 2' x 4' tent. In addition to the two grow lights (Migro 150's), I wanted it to calculate PPFD when I included Blue 55's and the R80's. It kept drawing the heat map 90° from the correct oriantation. It took a while to explain what it was doing wrong. It just got a case of the stoopids, so I had it just render the PPFD values using numbers in a grid. Yeh, it sucks when you spend $20 per month and it can't do something
that trivial. ;-)
The contribution that GPT has made has been significant. I might have been able to hire a consultant and for someone with that level of knowledge I would expect to pay a few thousand dollars and then there's the possibility that a consultant may not be available. Nor be able to cite sources. Nor have the same level of knowledge.
But I do know that after changing my processes to use what GPT has recommended, the plant is staggeringly healthy.
As of this morning, Flora is 8 inches tall and roughly 23 inches in diameter. Every metric I can gather about the grow environment is excellent.
The only downside is that there's a
lot of labor to LST this plant to keep it low to the ground like this I'm
really looking forward to flipping on Monday. I use shower curtain hooks to hang fishing weights from the branches. Some of these branches have four 2 ounce weights holding them down and it's a daily process to defoliate the plant and to add or move the weights.
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My goals for a grow are to maximize crop yield, crop quality, and bud quality where crop yield is the amount of flower, crop quality is the ratio of flower to the above ground mass, and bud quality is the percentage of secondary metabolites.
For my current grow, I've added a goal of getting smaller buds than normal (I've had buds as long as my forearm in some grows) accepting that there may be a trade off in terms of yield.
The research on this topic is readily available. I've been reading it for about four years and all of the research indicates that "more light=more weed".
It's been demonstrated, both in research and in growers' crops, that the more light you give cannabis (normal caveats apply) the larger your crop will be. Depending upon who you read, the increase is linear, though other research has shown that there is a rolloff as light levels increase. There's nothing shocking about this-it's simple plant biology. Light consists of photons. Photons are used by plants to create glucose. Glucose is used as a source of energy for growth.
In terms of crop quality I think Westmoreland covers that pretty well. I think it's in his 2023 You Tube video and I think that he also touches on it in his dissertation.
In terms of bud quality, which is the density of the buds and the ratio of secondary metabolites, that was in Westmoreland's dissertation and it's littered across multiple research papers that are freely available the Internet.
)
). However, I think some parts definitely sound interesting and are worth exploring myself in the future. I always want to stay open-minded too..
