Ideal N-P-K for growing marijuana


We've been growing marijuana for quite some time now and we’ve tried all different varieties of NPK ratios in our nutrient solutions. When it comes to vegetative growth and flowering, is there an ideal NPK ratio for marijuana plants?


I got burnt leaves on a plant that is flowering, How can I cure it? Ive been adding water to it every two days trying to reduce the amount of nitrogen in it. Does that work?

Hi Skunkblaster,

The NPK ratio is basically a measure of the concentration of 3 key nutrients—nitrogen, phosphorous, and potassium—that can be found in fertilizers. There really is no ideal fertilizer and every marijuana grower has his own theory, but, as a general rule of thumb, a 7-5-5 ratio works for vegetative growth.

When marijuana plants go into flowering stage, the nitrogen concentration can stay at a similar level, but, as flowering progresses, it should be reduced. Higher phosphorous promotes flower formation, but it is highly acidic. This is balanced out by a corresponding increase in potassium. For adequate flowering, you’ll want a formula of 3-10-10. Nutrients need to be diluted to 1,200 to 1,800 parts per million (ppm). A garden’s fertilizer requirements are individuated for a variety of reasons.

First, water quality—including its mineral content—varies, which alters the fertilizer needs. Second, different marijuana strains might use nutrients at different rates. Third, the plants’ nutritional needs shift with environmental changes in the garden. Light and temperature conditions can have huge effects on plant needs. Fourth, marijuana’s nutritional needs change based on its stage of life. Early and late vegetative stages and early, mid, and late flowering all have unique nutritional requirements.4




Wanting to learn how to mix my own nutrients, I would like to see if I understand this ratio thing.

For the 3-10-10 would that be say 3tbs of blood meal, 10tbs bone meal and 10tbs of (not sure what I am supposed to use for the K )?

Will be attempting to join the lab by next week so I’ll probably get my answer there, but I came across this one and the question formed.

Thank you for all of this, Robert.

Hoaglands Solution suggests the proper flowering ratios should be as follows:
N 210 ppm
K 235 ppm
Ca 200 ppm
P 31 ppm
S 64 ppm
Mg 48 ppm
B 0.5 ppm
Fe 1 to 5 ppm
Mn 0.5 ppm
Zn 0.05 ppm
Cu 0.02 ppm
Mo 0.01 ppm

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Domme, So this guy you reference likes to run a flower formula under 800ppm?

That is about what I run my auto flowers at.

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With that said, I modified it for my own needs in Hydroponics, and Aquaponics.


Dumme, excellent info … maybe you should open your own line of making nutes , Hammer:grinning:

According to Wikipedia, cannabis needs more N than P and K during all life phases.
What do you have to say to that?

Nitrogen is important during all stages, but in less quantity during flower. Too much nitrogen during flower will make it a harsher smoke and make for airy buds.

Just my opinion…


Yes, people WAY over fertilize with Phosphorus §.

According to extensive research over the past 5 years, 8-15 ppm of P throughout the plant’s life cycle is enough. Any more than that is a waste to the plant and detrimental to the environment. (The excess has to go somewhere.)

Since I can’t post links, go to Cannabis Business Times (dot com) and search for “Balancing the Nutrient Equation”.

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