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NPK Fertilizer Ratio

Best nutrients for marijuana.

Nitrogen (N), phosphorous (P), and potassium (K) and are the three main nutrients your marijuana need and are expressed as the N-P-K fertilizer ratio on your nutrient package or bottle. An N-P-K formula such as 15-30-15 means that the ingredients are 15% nitrogen (N), 30% phosphorous (P), 15% potassium (K) and 40% inert ingredients.

Marijuana requires a higher nitrogen ratio during the vegging and early flowering stage (Part 1 or Part A) as it is the main component for growth. During flowering (Part 2 or Part B) we really want a lower nitrogen and higher phosphorous NPK fertilizer ratio.

Not covered by the NPK fertilizer ratio is the micro-nutrients. These are the trace elements provided by most soils, but will need to be added when using a hydroponic grow system. Note that if you have ‘hard water’ or water with calcium above 200 PPM, then adding more calcium can be counterproductive. This is why several companies offer micro-nutrients for hard water.

Unfortunately there is no general consensus on the optimum NPK fertilizer ratio as legal restrictions prevent the large-scale testing of various formulations though many companies boast of in-house testing ‘proving’ their products to be superior. Many blends merely mimic what has worked well for tomatoes or other garden vegetables. Also take into account marijuana’s ability to adapt quickly to less than ideal conditions and the picture gets even less clear.

Even given the exact same NPK ratio are all formulations the same? No, because the NPK elements are bound up in molecular compounds with differing degrees of bio-availability. Presentations may be as inorganic salts, oxides, chelated or colloidal minerals. Translation: your cannabis can use some compounds easier than others.

If you check out several popular nutrient manufacturers you will see that each has a different idea of what is best. Let’s look at a few:

General Hydroponics

Flora Grow for vegging: 2-1-6

Flora Bloom for flowering:  0-5-4

Advanced Nutrients

Connoisseur Part A for vegging: 4-0-4

Connoisseur Part B for flowering: 1-5-6

NPK Fertilizer Ratio

Rather than being overwhelmed with so many choices and conflicting data, we recommend you check out a grow journal that you admire or a friend’s grow that impresses you and mimic what they are doing.

Do not buy a menagerie of nutrient products from different companies as they may not work well together. Stick with one company and one strain until you get a feel for it and have your grow dialed in.

Use a basic NPK ratio formula to see what kind of result you can achieve. Only then should you try a specialty product or try switching manufacturers. Remember that there are no magical, miracle products that will make your plants ‘explode’ and ‘drip with resins’.  We personally have witnessed more sorry-looking and damaged marijuana from eager growers throwing every formulation into their garden trying for super plants, and have rarely seen slightly under-fertilized plants suffering from a similar fate.

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How to Grow Marijuana Forum - Growing Marijuana Indoors & Hydroponics

5 thoughts on “NPK Fertilizer Ratio

  1. Templepaul says:

    Used pk13/14 before and had great results, studying horticulture at college and the results were unreal, too much tho can damage/burn your plants so be careful

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  2. Mark Wells says:

    No doubt Fox Farms is good. I’ve had good production across the board with it. What does put me off about it is the high ppm counts it can induce in your hydropoics solution, especially when you include the Big Bloom mix as part of your regimen. I was changing solution and washing out every week – 10 days as I used an oxygenation/aeration system composed of air diffusion rubber tubing to provide more dispersed aeration compared to traditional air stones. One k+ ppm residual dispersions were not uncommon. Not insurmountable by any means but at my present age dealing with larger numbers makes my head hurt. ILoveGrowingMarijuana.com has a trio that works extremely well especially if you view the plant’s production cycle in terms of 2 phases instead of 3. ILGM’s product is slightly more expensive (and more problematic to obtain as it has Marijuana printed right on the label (screwed up Laws and Custom’s policies we have here in the good ol’ USA)). Personally I’ve found something that gives an overall 8-15-15 (plus locally required micro nutrients) N-P-K structure what I like best if not mixing my own. Hope this helps some. Peace and HAPPY TOKING!

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  3. Shot says:

    Best fertilizer for ANY MJ plant is the Fox Farms Trio, they’re sold separately OR as a 3 pack. Big Bloom, Grow Big, and Tiger Bloom. Best stuff smokin’! (No pun intended!) 😉

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  4. steph says:

    can you help me by what is the best fertaliser for blue cheese feminised , thanks all

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  5. steph says:

    I would like to know the best fertilizer for blue chesse, any help woulde be great guys ,all the best steph

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