The science of medical cannabis nutrition
Compare to conventional horticulture, commercial crop cultivation of medical cannabis is a new farming niche. While commercial and academic researches regarding optimal growth condition and nutrition for cannabis are still limited, most of the known growing practice is based on growers’ experience.
Only recently, useful information has started to accumulate and is available to the public.
Recent research has shed some light on the effect of different nutritional regimes on the content of active compounds in cannabis flower buds and leaves. Some of the active compounds are secondary metabolites that are produced when the plant is in under stress. For example, some preliminary research has shown that inducing potassium deficiency increases cannabinoid concentration in cannabis flower buds. Research regarding connection between nutrient availability and stress on active compound levels is in its early stages and must be carefully referred when planning nutrition program for cannabis.
In many countries, growers practice is lead under the assumption that as long as THC and CBD content are within the regulatory limits, medical cannabis flower buds are the measured commercial yield they are looking to maximize. Therefore, crop nutrition programs should facilitate the right concentration of cannabinoids and high volume of flower yield while ensuring sufficient THC and CBD content.
Photo: Typical nutrient deficiencies in cannabis plants. Precise plant nutrition is essential to avoid such deficiencies, and grow healthy plants (image by: © Haifa Group)
Haifa Group, a leading expert in specialty fertilizers for over five decades, took the cannabis crop nutrition one step ahead, and developed a precise methodology and solutions for cannabis nutrition. The overall cannabis crop nutrition management approach is based on Haifa’s vast experience in plant nutrition of horticultural crops worldwide. The prime objective is to analyze and meet the plants’ nutrient requirements in the most efficient and accurate method.
Medical cannabis is grown on soilless substrate. Optimal root environment, accurate irrigation and moisture content, are critical in order to supply the plant requirements and maintain proper oxygen levels.
Plant nutrients should be supplied through the feeding solution, and in order to keep optimal conditions for nutrient uptake, pH level must be maintained at 5-6.5, and 20-30% drainage of irrigation water should be kept in order to prevent high salinity conditions. A continuous monitoring of EC and pH in both irrigation water and drainage water is therefore highly important. Only pure and precise fertilizers that are developed for that task can ensure proper and harmless nutrition supply.
Growth cycle of cannabis cultivation can be divided to two main stages, vegetative phase and flowering phase – where the plant develops its flower buds.
The last can be internally divided to more stages. Vegetative growth stage starts after the establishment of the rooted cutting when seedlings are planted in the growing substrate.
During this stage, when growing in a controlled environment, plants are exposed to long daylight hours (16-24 h) which induces vigorous vegetative growth. This stage is crucial for a strong and healthy plant to be able to produce high volume and quality flower buds. Nutritional requirements at this stage are high in order to support the rapid growth of the plant – especially nitrogen and potassium. Special formulae suggested by Haifa Group provide growers with the ability to maintain the most precise nutrient levels that the medical cannabis crop needs.
A key point is to have a well-balanced, complete plant nutrition that includes not only the precise NPK ratio but also supply adequate micronutrients. Unlike conventional fertilizers used in traditional agriculture, the medical cannabis focused fertilizers must be fully water soluble be virtually free of chloride, sodium and other detrimental elements for plants.
Flowering phase is induced when daylight period decreases to 10-12 hours. This phase is divided into three inner physiological stages; bud formation, bud sizing, and the finishing stage when the flower buds reach maturity and ready for harvest. This is a critical stage and any nutrition provided during the flowering phase directly influences the bud formation and development. Nitrogen and potassium levels should be in favor of potassium. Phosphorus in this stage should be present in the feeding solution but not in excess. Concentration of 60-80 ppm (P2O5) supply the plant needs at this stages.
Cannabis growers cultivate a wide variety of hybrids. Each hybrid has different nutritional requirements than the other hybrids. Nutritional program must be adjusted according to the specific hybrid’s requirements. Moreover, nutrient deficiency symptoms may develop and look slightly different for each hybrid. In order to adjust the program for each verity, systematic tests were held. Together with vast experience gained worldwide by the Haifa Group agronomy team, medical cannabis plant nutrition solutions offered by the company are well-proven and convert knowledge into yield.
The effect of different nutritional regimes on the content of active compounds in cannabis flower buds and leaves – Medical Cannabis
Cannabis nutrient profile
with matching General Hydroponics Flora mixes
Nutrient profiling is a means of presenting a nutrient solution with its worth given in terms of its elemental makeup for elements essential to plant growth, and some beneficial elements. Because this is a common language spoken by all nutrient solutions and fertilizer products, when it’s known, a nutrient mix can be tailored using the guaranteed analysis from a variety of fertilizer products. In this way, a nutrient solution mixed from one assortment of fertilizer products can be reproduced by someone using a completely different assortment of products. For example, a solution made from liquid premixed products can be reproduced by someone using dry raw chemical compounds, and vice versa.
This method of communicating nutrient solutions has been used by researchers and professionals because it leaves no doubt as to the nutritive worth to be targeted when mixing fertilizers with water. When a profile target is given, instead of the measures for a specific fertilizer or fertilizer brand used to mix the profile, it effectively becomes a generic formula that can be used by anyone even if they don’t have the same fertilizers or brand name products used by the originator of the profile.
A Grower’s Project
Several years ago I undertook a project to find which hydroponic nutrient profile(s) produced the highest cannabis yield. The project ended after 10 years and more than 25 crops. I was that convinced of the control nutrients gave me, and just as determined not to let the project end until I proved it to myself. That never happened. As a starting point I set out to collect as many published cannabis nutrient profiles as I could find. To my surprise I could only find two sets of recommended cannabis profiles, one published by Mel Frank in his Marijuana Grower’s Insider’s Guide, the other by pH Imbalance (no relation to myself) in his MJ Growers Handbook, both are shown further below.
Stage of Growth
The first thing you’ll notice about the profiles is that they change according to the stage of growth for the crop, three stages for those in the Marijuana Grower’s Insider’s Guide, and four for those in the MJ Growers Handbook. While three or four reservoir changes aren’t unusual for a hydroponic grower to endure, I’ve seen many stage of growth schedules recommended by individuals and fertilizer manufacturers that called for more, some as often as every week (for a typical 90 day crop that’s 13 reservoir changes). A nutrient solution is generally changed for two reasons. Primarily, to prevent its profile from becoming dangerously depleted or out of balance from overuse, secondly, because the grower simply wanted to change the nutrient profile in order to follow a certain stage of growth schedule even if the solution still has the better part of its life remaining.
A grower should be aware that anyone recommending a reservoir change every week without knowing the size of the reservoir and the area of growth it supports is probably playing it safe at the grower’s expense for both labor and fertilizer costs (for more information on reservoir changes see this nutrient solution management article). Going on the assumption that the stage of growth recommendations produced acceptable results, the project included as many as twelve reservoir changes and as few as three (including the initial first mix) even though the size of the reservoir and the growth it supports dictate that only three changes were required. I found no difference in yields, but I did spend more time working harder and using more fertilizer than I needed to whenever more than three reservoir changes were made.
More is Better?
The second thing you’ll notice about the profiles is that some are much stronger than others, with the growth stage formulas being the strongest. However, even within the same stage of growth the authors don’t seem to be of the same mind. This suggests that cannabis produces equally well under a wide range of nutrient strengths and profiles, and that using more is not necessarily better when using less gives the same results as using more.
The nutrient profiles used during this project varied according to Mel Frank’s recommendations for both moderate and strong light gardens. It was discovered that using 250ppm N during the growth stage produced no faster growth nor higher yields than using the 100ppm N found in his flowering profile (the one highlighted red in the For Flowering section below), and that the same flowering profile could also be used during the first two weeks of growth. It became apparent that using growth stage as a prerequisite for managing a cannabis crop’s nutrient profile was not only overstated, but strengths and profiles were overstated as well. While this may not be the case with other hydroponically grown crops such as tomatoes, it does suggest that cannabis has simpler needs than many people and fertilizer manufactures advocate. In fact, using his 100N-100P-200K-60Mg flowering profile for all stages of growth with just three reservoir changes produced the same yields as twelve reservoir changes and stronger profiles did. Doing less and using less produced the same results as doing more and using more.
Recommended Profile Target
Where the 100N-100P-200K-60Mg target profile relates to General Hydroponics Flora Series 3 part liquid fertilizer products, the same profile can be mixed without using any of the GH Grow component. If one carefully reads the labels, he’ll find the Micro component actually contains more N than the Grow, and the Grow component contains nothing else that isn’t already contained in the Micro and Bloom components. Substituting a little more of the Micro component to make up for the missing Grow precludes the use of the Grow component altogether.
Deviations from a given target are to be expected when using any premixed fertilizer, even 3 part products, due to the pre-determined ratio between elements contained in each part. More often than not, increasing the content of one element to match its target perfectly causes other elements to move off-target. Given cannabis’ apparent immunity to a wide range of profiles, small compromises from the target are of no consequence, but often annoying. The profile arrived at during the project used just the Micro and Bloom GH Flora components at a convenient 1:2 usage rate, though any comparable fertilizer product(s) could be used to reproduce the profile. It translates into the following formula.
|N-P-K-Mg ppm||ml/US Gallon GH Flora||Est [email protected]||Est Cost/ResGal|
This formula has proven itself to be one that can be used for all stages of growth, under HID lighting of various intensities, and when using a variety of hydroponic systems with a reasonably good quality source water. What is most notable, however, is in the interest of efficiency, low maintenance, ease of use, fewer products to purchase, equally high yields and equally healthy plants. For expedience, that GH formula was rounded to 8M-16B-0G, which has become widely known in Internet cannabis circles as the Lucas formula.
About The Published Nutrient Profiles
The published profiles are shown here for those wishing to use them as a starting point for their own project. And though directly below each given set of ranges, in italics, are mixes for the General Hydroponics Flora Series brand of fertilizer, you can use the Profile Calculator below to match your brand of fertilizer with a profile. The mixes were designed to match, as closely as possible, the high end of the recommended ranges. In normal reservoir maintenance, where only plain water is added back to the solution, mixes can be made nearer the high end of the recommended ranges. This will account for the normal attrition of elements occurring over the life of the solution, and by the time the solution is ready to be replaced its content should be nearer the low end of the range.
Mixes are shown in the format ml/gal M-B-G to indicate the milliliters per US gallon for General Hydroponics Flora Micro, Bloom, and Grow components respectively (Hard Water Micro is not used here). The number accompanying each component (for example 1M-1B-1G) indicates the milliliters per US Gallon to be used for that component. Following each mix is its primary nutrient content in elemental ppm for N-P-K-Mg, as well as the metered [email protected] for the mix, and the cost per reservoir gallon for the mix.
|Element (symbol)||Mel Frank’s Insider’s Guide
|MJ Growers Handbook
by pH Imbalance
Fluorescents & winter
| Strong Light
Sunlight & 1000w HID
|First Two Weeks|
|Est [email protected]||952||1038||1381|
|Est [email protected]||2175||2517||1916|
|Pre-Flowering (two weeks before induction)|
|Est [email protected]||–||–||1401|
|Nitrogen (N)||40-100||40- 100||0-50|
|Phosphorus (P)||70-90||70- 100||100-150|
|Potassium (K)||120-220||100- 200||50-75|
|Magnesium (Mg)||30-50||30- 60||–|
|Est [email protected]||1158||1200||1140|
|Seeding – Fertilized Flowers|
|Est [email protected]||–||–||1642|
Regarding Mel Frank’s recommendations: During flowering for sinsemilla make your formula nearer the low end of these ranges. For seed crops, make the solution nearer the high end of the given ranges.
Costs based on Jan 2002 price avgs in US dollars.
Nutrient Profile Calculator
This ppm or that ppm
This page provides a common language spoken by all fertilizer solutions and a way to mix them for growing cannabis hydroponically. Sometimes referred to as the Lucas formula, this page explains the true origin of this well known proven formula and the project that led to its discovery. Emphasis is placed on the benefits of avoiding generic formula substitutes found on fetilizer labels for one more specific to cannabis.