Vegetal green gradation collage
By Craig Allen and Nik Nikolayev
Plants have internal chemical systems to help them grow and guide their growth patterns. Arguably, the most important function of a plant’s chemistry is to control nutrient assimilation. By its definition in this form, assimilation is the process of the plant absorbing vitamins. In a slightly more detailed sense, assimilation is the plant’s way of digesting raw food and converting it into usable building blocks.
Hormones guide the absorption and movement of nutrients inside of the plant and the most important two hormones are auxins and cytokinins.
The first two articles of this three-part series, featured in the August and September editions of Marijuana Venture, focused on a broad range of topics: plant growth stages, optimal climate conditions, and symbiotic relationships in the soil. In this third installment, we will turn our focus toward plant chemistry and what happens inside cannabis throughout its various stages of life.
Vegetative Nutrient Assimilation
Let’s follow a plant through its life cycle. Imagine a small cutting has just rooted; once rooted successfully, it will be transplanted into a pot to enter the vegetative phase. During this phase, the main objective is canopy and root growth, both of which are tied closely together through processes involving the two primary classes of growth hormones in plants: auxins and cytokinins.
Auxins, produced in the newest leaf growth, help funnel raw materials to new growth sites on the plant. Once in these sites, raw materials are condensed into compounds like chlorophyll. This green pigment gives leaves their color and is also responsible for harvesting energy from sunlight. Needless to say, chlorophyll is pretty important. In fact, it is so important that the 1915 Nobel Prize in chemistry was awarded to Richard Willstätter, who discovered its role.
Lush green canopies can only be achieved by having an ample supply of hormones to manage raw food material for chlorophyll synthesis; important raw materials are nitrogen and magnesium. Magnesium is particularly important because it sits at the very core of the chlorophyll molecule and serves as the reaction center to drive photosynthesis. From this center comes the electrical energy necessary to fuel all aspects of plant growth. Nitrogen is crucial as it tethers magnesium in place and basically stabilizes it. Additionally, it is a fundamental component of all amino acids that are basic building blocks for proteins responsible for photosynthesis. Therefore, having adequate levels of nitrogen can maximize photosynthetic capacity during veg.
Plant growth can also be achieved by foliar feeding. Many of the building blocks can be applied directly to the leaves. This way, no energy is spent acquiring them from the root zone. A great option to consider is foliar application of amino acids as they are direct precursors to chlorophyll, such as L-glutamic acid. Rather than basic building blocks, such as nitrogen and magnesium, amino acids provide half-built structures, meaning even less work is required to synthesize photosynthetic pigments.
Hormones
Auxins produced in the new leaf growth travel down the stalk and into the roots, where they stimulate nutrient uptake and transport into new leaf growth. As the canopy becomes larger, it requires more nutrients to be transported form the root zone. Auxins from the new leaf growth are telling the roots to grow, so the roots can better support the canopy above.
Profound as they are, auxins do not function alone in regulating growth. Cytokinins are complementary hormones, and just like auxins, they are involved in almost all aspects of plant metabolism. Whereas auxins drive transport of raw materials, it is the cytokinins driving the building of raw materials into more complex molecules. For example: cytokinins aid in the formation of chlorophyll and other photosynthetic pigments, thus assisting in all aspects of canopy growth.
Cytokinins are primarily produced at the newest root growth, which is similar in concept to how auxins are produced at the newest leaf growth. At the very tips of the roots, there is a “root cap” where new growth is constantly occurring and this pushes new root material through the soil in search of food and water. This continual growth process is regulated largely by cytokinins.
In addition to their effects in the roots, cytokinins are also partially responsible for canopy growth. These hormones pass important information from cell to cell within the plant and regulate how many of the carbohydrates produced during photosynthesis travel down into the root zone to provide the necessary energy for root growth. A hefty portion of what is produced during the day becomes fuel for root growth when the lights go out.
Between the two, auxins and cytokinins are present from the first moments of a plant’s life to its very last. All aspects of nutrient uptake and utilization can be described in relationship to both of them so having the right levels of both is critical, especially when the plant transitions between the vegetative and blooming phases of its life.
A cannabis plant will change drastically when flowering is induced and that means a big change in its hormone profile. Initially, a group of growth hormones known as gibberellins will kick in as the light cycles change and the effect is stem elongation and stretching. This convenient change provides additional room for flowers to form without having to produce new stalks.
Flowering Nutrient Assimilation
On its way to bloom, the plant goes through a transitional phase, and its nutritional needs change. Whereas the vegetative phase was marked by root and canopy growth, the blooming phase is marked by flower production. The flowers depend on a different set of building blocks than that of the leaves so most bloom formulations/additives contain more phosphorus than nitrogen. Cannabis flowers depend on phosphorus to provide the energy necessary to produce and accumulate terpenes such as THC.
Terpenes are a seriously complex class of compounds – there are more than 30,000 known and THC is just one the cannabis plant produces. Although THC does not contain any phosphorus itself, its synthesis is dependent on it through a fascinating set of reactions where phosphorus-bound molecules adjoin to one another in an assembly line like fashion and secrete through glands known as trichomes. This metaphorical assembly line is how all Terpenes are produced and sometimes building blocks compile to form THC or CBD. Many times what it builds is not a cannabinoid at all, but rather an aromatic terpene that gives it a fruity, floral, skunky or herbal smell. There are so many possibilities!
Whatever the final assembled terpene is, it must be passed along a phosphorus-dependent pathway. Hormones, like auxins and cytokinins, will regulate each step along the way and effectively coordinate both the uptake and utilization of the required nutrients to ensure flower synthesis. All of this occurs instead of continued root and canopy growth, so it is natural the plant’s physical growth will slow a little bit.
Toward the end of flowering, plants may require less and less food because the root system is not replenishing itself and the canopy is not maintaining high photosynthetic capacity. Leaves eventually turn yellow and roots stop absorbing nutrients and at this point, the plant should have some fantastic looking and smelling flowers.
Wrapping It Up
For a plant, many complex systems utilizing food and light energy work in a symbiotic way to create compounds for health and growth. The internal workings of the cannabis plant function best, like the human body, when given proper resources, and from those, amazing things are possible.
The big picture is this: every part of the plant supports every other part of the plant. Roots support canopies and canopies support roots. If all required conditions are met and balanced such as hormones and nutrients, plants will grow faster and stronger because they can focus on optimizing their growth, not reducing stressors that might hinder it.
We hope you have enjoyed reading this series as much as we have enjoyed writing it.
Craig Allen and Nik Nikolayev are experienced growers and consultants. Allen is the co-owner of Groco Supply in Bellevue, Washington (grocosupply.com). Feedback on this article or any subject regarding nutrients for cannabis plants can be sent to nutrients@grocosupply.com.