Marijuana Growth Stages – Veg / Bloom

Marijuana growth stages are generally separated into two phases which are vegetative and flowering. Each growth stage has its own spectral light requirements for optimal growth and yield.

LED Light Requirements for Marijuana

Light Spectrum WavelengthsThe minimum LED light requirement for productive growth in the vegetative marijuana growth stages are 23 watts per square foot with optimal growth being around 35-50 watts per square foot.

The minimum LED light requirement for productive growth in the flowering marijuana growth stages are 35 watts per square foot with optimal growth being between 45-55 watts per square foot.


Where do I place the light?

Positioning largely depends on the light. Does it have 1-watt diodes, 3-watt, 5-watt or 10-watt diodes?  The lower power of diode, the closer the light can be.

Does it have secondary optics or lenses over the LEDs? If so, you should start at around 24 inches and slowly move it down until you see the leaves starting to bleach. Move the light up 2 inches and that is the closest you want to keep the light at any given time.

Light Spectrum Absorption For PhotosynthesisIf it does not have secondary optics like reflectors, start at around 18 inches and repeat above method. As a standard rule, do not place the LED light(s) any closer than 12 inches from your canopy because the intensity will damage your plants in a short amount of time.

To be honest, there are simply too many variables in marijuana growth stages, strains as well as differences in LED systems, panels, manufacturers, power, and diodes to give standardized numbers. Use the information I’ve provided along with the manufacturer’s specifications to determine what will work best for you.


Marijuana Growth Stages

Vegetative Stage Of MarijuanaVegetative Stage –  1-2 months. Plant size is the key at this point so a spectrum with full red and blue is important. We are attempting to mimic the sun, so with LEDs, our best results in are found with a Red/Blue mix of around 60/40.

Pre-flowering Stage Of MarijuanaPre-flowering Stage – To reduce stretching, Red/Blue ratio can be increased to 70/30 for the first 2 weeks of flowering, (75/25 for taller plants). Blue will stimulate additional pigments during this critical growth period enhancing flower colors and fragrance.

Flowering Stage Of MarijuanaFlowering Stage –  6-9 weeks depending on the strain. To maximize flower size and potency, increase the Red/Blue ratio to 80/20. The higher Red ratios (by lowering the blue) can be used to fully promote flowering.

Ripening Stage Of MarijuanaRipening Stage – To enhance resin and terpenes (fragrance), lower the Red/Blue ratio back down to 70/30 or even 60/40 for the last 2 weeks. The higher blue ratio will not alter the flower structure or promote excess bud leaves because flower growth is winding down, it’s focusing more on resin production.

Yellow, Green, & UVB– are important and can be supplemented either in the last 4-5 weeks, or throughout the entire flower period to help stimulate pigments, terpenes, and THC.



Let me know about your results if you try this growth cycle. Or perhaps you have one of your own that you swear by. If you have any questions or comments about marijuana growth stages, or maybe you have a method you would like talk about, please feel free to comment below, I’d love to hear from you.



  1. Shannon

    So glad i found this site. This article really broke it down easy to understand.

    I want to begin growing but i was afraid i’m not good enough or i will screw something up,

    You break down what to use and why and how long. Now i want to give it a try.

    Where can i find seed to plant?


    • Karl Hosch

      If you want seeds for cannabis I have 33 strains with more on the way. Go hereand to see them all. For fruits, vegetables, herbs, and houseplants go here. If you if you need any help growing or have any questions, please contact me anytime. Good luck with your plants, come back and keep me posted too!

  2. Andrew

    Hi there. I just finished reading your article on the growth stages of Marijuana and thought I would just drop you a quick comment to say thanks.

    I totally agree with the comment that Greg made on this page. I can’t believe this plant is still illegal. I live in the UK and so far there is no sign of it being legalized here!

    I have grown small auto-flowering plants in my greenhouse with great results. I used a variety called “lowrider”. Even with the UK sun, the results were great after about 6 weeks.

    As well as the obvious benefits to growing this plant I find the grown cycle very interesting.

    Fingers crossed for legalization very soon!!

    • Karl Hosch

      I agree, it should be legalized throughout the world but I think it’s just a matter of time before it is. Yes, the lowrider is a hardy strain so it’s easy to grow it is also pretty small plant compared to its cousins. It is also an auto flowering which takes the guess work out of the growing stages. Well, I’m glad you had a good grow, the greenhouse was key. Thank you for stopping by if you ever want to try indoor growing, I’ve got several different LED grow lights to choose from. Best of luck to you! 

  3. gregS

    Hi Karl,
    You certainly know the technical aspects, about growing marijuana. I congratulate you on getting into an industry at the right time.
    Over the next few years more and more States in America will legalize this drug, and the market will explode. Already Canada has stepped up, and States will realize they need the tax money, so it will become legal everywhere in the next few years.
    I can’t believe the Fed’s still think it is a Class A drug!
    Good luck, and hold onto your hat.

    • Karl Hosch

      Thank you for the comment. There is a lot of talk going around about changing laws but all it takes is proof that making it legal generates more revenue for the governments than by keeping it illegal. It’s all about the money. They say next year Canada may smarten up but we will see. I believe marijuana is a schedule I drug according to the DEA. Luckily, promoting led grow lights for the seemingly perfect plant is not illegal. Thanks again for the comment. If you ever have any questions, come on back anytime! 

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