Cannabis and hemp, like any other living-organism, requires a specific diet of nutrients for proper development and metabolic function. Essentially, to live, grow, thrive, flower, and bud is the main focus of a cannabis and hemp plants’ (and any other plants’) existence. Other than a specific diet of nutrients, plants also require other necessities for their existence and survival; necessities like sunlight (or artificial grow lights), air, proper temperature, moisture (or water), and, most importantly LOVE. So, love may not be as important as the other four requirements, but we believe love and passion have a lot to do for a plant’s success, just as much as the nutrients you feed them. 

Essential Nutrients and Optimal Ratios

On most fertilizer and nutrient products they list three specific letters and numbers on the front center label, N-P-K and 1-1-1 (for example). The N-P-K stands for Nitrogen-Phosphorus (or Phosphate)-Potassium (or Potash) ratios and the three numbers represent the concentration of the individual elements in a fertilizer product, in percent (%). To start, Nitrogen, Phosphorus, and Potassium, in addition to Hydrogen (H), Oxygen (O),  and Carbon (C), are a few of the key nutrients (or macronutrients) necessary for a plant’s growth. Other nutrients as and Calcium (Ca), Magnesium (Mg), and Sulfur (S) are secondary nutrients, and Manganese (Mn), Molybdenum (Mo), Iron (Fe), Zinc (Zn), Copper (Cu), Nickel (Ni), Chlorine (Cl), Copper (Cu), and Boron (B) are also necessary nutrients (or micronutrients) for your plants growth.  

Cannabis and hemp can survive a wide range of nutrient ratio formulations, but that doesn’t mean that nutrient imbalance is unimportant. Nutrients  have to be at an effective balanced ratio to achieve optimal metabolic function, growth and results. When nutrient ratios are imbalanced in soil and planting media —specifically due to high nutrient ratio levels — cannabis and hemp’s ability to uptake and absorb nutrients it needs is compromised. This compromise can cause negative affects as small as limiting the simultaneous uptake of various nutrients at the same time, to problems as big as leachate (or runoff) nutrient waste and plant stress and problems. In a simpler concept higher concentrated nutrients can lead to residual nutrient buildup in planting media and causing nutrient overuse and, ultimately, a waste of money.

To achieve nutrient efficiency and optimal development, a good recommended cannabis nutrient ratio for N:P:K is 1:0.5:1. 

How much N-P-K macro-nutrients and when?

Now, we want to get a little more nitty-gritty about proper balanced cannabis macro-nutrition, electric conductivity (EC) and total dissolved solids (TDS), and feeding frequency.

Nutrient, or fertilization management, can be considered both a science and an art. In greenhouse or indoor cannabis cultivation, the typical planting media substrates used today hold limited amounts of nutrients due to the low affinity of cation exchange capacity (CEC) of soil particles, giving greater reasoning for cannabis nutrient efficiency. Comparing the nutrient levels on different tissue types can give a grower a relative insight to cannabis needs, and preventing the over-fertilization and nutrient toxicity effects. Cannabis and hemp leaf tissue can possess about 2- 4% N, 0.25- 0.5% P, and 1.5- 3% K; however, flower bud tissue can possess about 2- 3% N, 0.5- 0.6% P, and 2- 2.5% K. 

Nitrogen (N)

Nitrogen is one of the most important elements for plants. Nitrogen influences the metabolic function promoting plant growth. If nitrogen concentrations are low, then plants will be stunted and develop symptoms of chlorosis (or cannabis leaf yellowing) on lower leaves. Too much nitrogen, can cause leaf burning and death (necrosis), symptoms of dark green leaves, and reduction in flower development.

Nitrogen concentrations should be low during the plant establishment stage as they are developing root systems and will have limited-to-no nutrient allocation through phloem and xylem transport systems. Once young roots reach maturity and cannabis plants are bulking, it is necessary to increase nitrogen until mid-to-late flowering/ budding. During peak flowering, or mid-to-late flowering/ budding, nitrogen should be greatly reduced to a lower concentration. 

In terms of weekly nitrogen TDS (in ppm), it is recommended from NCSU (North Carolina State University) cannabis research 75- 100 ppm N (or an EC of 0.2 mS/cm) during the seedling or start growth stage after the appearance of the second set of true leaves. In vegetative stages, 150- 200 ppm N (or an EC of 0.3- 0.4 mS/cm). This nitrogen regiment can be maintained throughout mid-to-late flowering (but it is best to decrease nitrogen concentrations by the second to last week of mid-flowering). In late-flowering, 25-100 ppm N (up to 0.2 mS/cm). 

Cannabis’s uptake of nitrogen, based on leaf- and flower bud-tissue, indicate that most nutrients are acquired during the first half-to-3/4 of the growing season. Providing excess nitrogen late in cultivation cycle will stimulate additional leaf and apical growth, which can inhibit, or reduce, bud growth, quality, and yield.

Phosphorus (P)

Phosphorus is a major contributor of stem elongation, branching, and overall canopy development, and a major component of flower and fruit (seed) appendages of the plant. When phosphorus is limited, plants will not develop extensive branching canopy and will exhibit symptoms of stunted plant growth, lower leaf purpling (not to be confused with purple-phenotypes), irregular olive-green spots (with or without marginal necrosis) along leaflets on lower, older leaves resulting in a reduction of leaves and other floral matter.

Phosphorus concentrations should be low during plant establishment. In vegetative growth, phosphorus needs are low until early-flowering to late-flowering/ bud, where cannabis plants needs increase.

In terms of weekly phosphorus TDS, it is recommended 20-50 ppm P (or an EC of up to 0.1 mS/cm) during the seedling growth stage. In vegetative stages, 30- 110 ppm P (or an EC of up to 0.1- 0.2 mS/cm) throughout the rest of the cultivation cycle. If feeding at a lower concentration, this regiment can be maintained weekly throughout the growing season; if feeding at a higher concentration, the concentration will need to be maintained until late-flowering/ budding as the reserved phosphorus in the cannabis plant will provide enough nutrient to the root systems allowing translocation of phosphorus to maturing buds and to complete the budding stage. During mid-to-late flowering, phosphorus content can be 50- 100 ppm P (or an EC of up to 0.1- 0.2 mS/cm) if additional phosphorus is needed. 

For best cultivation practices with phosphorus nutrient, it is recommended to feed weekly at a rate of 15 ppm P (or an EC equal-to or less-than 0.1 mS/cm) for seedlings and 30- 60 ppm P (or an EC up to 0.1 mS/cm). This low application of phosphorus supplied to seedlings can be increased slightly during vegetative stages to 40- 60 ppm P (or an EC of up to 0.1 mS/cm) continuously until flush/ harvest.

Potassium (K)

Potassium is a major contributor for strengthening stems, stomatal regulation of transpiration and air exchange, energy production in photosynthesis, promotes overall health and immunity, water and ion uptake and regulation, regulation of gene expression, and enzymatic activity. When potassium is limited, initially cannabis leaf margins result in leaf-margin and the saw-tooth edge yellowing on older, lower leaves. As nutrient symptoms progress, the marginal yellowing will become more noticeable in spread of older leaves. At the peak of deficiency, leaflet margins yellow and regions of necrosis will develop on leaves and margins. 

Potassium concentrations should be low to mid during plant establishment. In vegetative growth, potassium needs are mid until mid-to-late flowering/ bud. Increase potassium gradually in mid-to-late flower for increased need.

In terms of weekly potassium TDS, it is recommended 60- 120 ppm K (or an EC of 0.1- 0.2 mS/cm) during the seedling growth stage. In the vegetative growth stage, potassium concentrations can be increased from 120-240 ppm K (or an EC of 0.2- 0.5 mS/cm); for optimal potassium concentrations it is recommended that 175 ppm K (or an EC of 0.3 mS/cm) is most efficient. From initial-to-late flowering/ budding, 150- 240 ppm K (or an EC of 0.3- 0.5 mS/cm). Depending on the difference of nutrient needs based on genotypes, potassium nutrient needs may be higher and go as high as 200- 350 ppm K (or an EC of 0.3- 0.6 mS/cm) from late mid-flowering until flush/ harvest.