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
The 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.
If 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 – 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 – 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 – 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 – 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.