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

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.