NPK Fertiliser: What Is It And Why Does It Matter?

If you are new to cannabis cultivation, let’s get right to it and demystify what N-P-K means. Those numbers in bold on the front of the bottle of base nutrients represent Nitrogen, Phosphorus, and Potassium. These numbers tell you the N-P-K ratio. For now, we won’t get too caught up in the ideal N-P-K ratios to grow cannabis. That’s for another blog. Let’s concentrate on each one of the essential macronutrients in isolation. It’s time to breakdown what they are and why they are so important to your marijuana.

N IS FOR NITROGEN

Nitrogen is the most common element on earth. A whopping 78.1% of the entire volume of the planet’s atmosphere is pure Nitrogen. Now you know why the Petrochemical Robber Barons are terrified of the prospect of the Nitrogen fuel cell. And why Tesla electric cars are a joke. But what does this earth element mean for the ordinary decent home grower?

Well, in simple terms, nitrogen puts the green in your ganja. The high chlorophyll content that brings out the dark green colour in leaves is nitrogen at work. Inside cannabis plants, nitrogen is highly mobile and a real multitask mineral. Aside from facilitating chlorophyll photosynthesis, nitrogen’s other big role is converting into amino acids, which then form proteins.

Hydroponic mediums are mostly sterile. All fertilisers and supplements, as well as beneficial microorganisms, must be added by the grower. Growing cannabis in soil is not a simple, quick-fix alternative as 98% of the N in soil is organic matter unavailable to plants. Only when moisture, temperature, and oxygen levels are optimal can N be broken down by microorganisms and made available. The grow medium must be dialled-in for this mineralisation process to occur.

Remember, N is easily lost. Denitrification can happen if you flood soil and/or keep temps too high. This effectively starves the microorganisms of oxygen. Chlorosis of the leaves is the warning sign of an N deficiency resulting from nutrient lockout. Chlorosis spreads easily throughout the plant due to the mobility of N.

On the flip side, too much N will make leaves really dark green and will delay harvesting if it persists into bloom. Growers like to go heavy on N in vegetative growth and gradually reduce as bloom progresses, before thoroughly flushing with pure water and/or light flushing solution for the last 1-2 weeks.

P IS FOR PHOSPHORUS

Phosphorus is the 13th element. Discovered in 1669 by German alchemist Hennig Brand during an effort to create the mythical “Philosophers Stone,” Brand distilled the salt from his own urine and came up with white phosphorus. Not quite the breakthrough he hoped for, but enough to keep him converting urine into coin for the rest of his days.

In contrast to nitrogen, this second macronutrient has a stronger bond to soil and is not so easily rinsed out by watering. Regardless of your growing medium, phosphorus is essential to the process of photosynthesis and root development. Make no mistake, vegetative growth is not just all about high N fertilisation.

During flowering, it's preferable to begin the increase of P and K, while N is simultaneously decreased. As bloom progresses, P becomes key to bud formation. Most growers find that cannabis crops mature faster when they have the right amount of phosphorus available.

Don’t be fooled into thinking you’ve got purple weed by a phosphorus deficiency. Also, don’t get too carried away with huge P doses or using concentrated P & K bloom boosters. You might end up with nutrient burn instead of bigger buds if you dose too high.

K IS FOR KALIUM (POTASSIUM)

K is for confusion because this element goes by the name Potassium these days. Potassium comes from potash, which is the ashes of plants. That totally makes sense and should end the confusion surrounding the 19th element on the periodic table.

Unlike the aforementioned two macronutrients, potassium is found in lake bottom and seabed salt deposits. Pure elemental potassium cannot be found in nature as the element is so highly reactive. Remember when the science teacher put some potassium in a bowl of water and it burst into flames?

Potassium plays a key role in bloom and can be the difference between a lightweight harvest and a “Big Dirty.” Potassium is so important to fruiting plants and agriculture in general that “in 2005, about 93% of world potassium production was consumed by the fertiliser industry.” Moreover, aside from ensuring fat cola formation, potassium is the cannabis plant salt regulator. Thus, lower doses must also be applied during vegetative growth.

FINAL THOUGHT: ORGANIC VS CHEMICAL

Always read the label and do some research before you purchase any NPK cannabis fertiliser. Some will be synthetic, others will be organic. Not all nutrients are manufactured or sourced to the same quality and standards. Growers beware.