D. Caplan, M. Dixon, Y. Zheng
Sep 1, 2018
Propagation and Root Zone Management for Controlled Environment Cannabis Production
Overview
Dr. Deron Caplan completed Canada’s first PhD specifically focused on cannabis cultivation under controlled environments. His research filled significant gaps in the scientific literature on cannabis horticulture—an area previously dominated by anecdote and trial-and-error due to the plant’s legal status. Conducted at the University of Guelph, his thesis adopted an Integrated Root Zone Management (IRM) approach to understand how propagation techniques, substrate composition, fertilization strategies, and drought stress interact to influence plant performance and cannabinoid output.
His findings are now foundational for commercial growers seeking evidence-backed cultivation protocols to optimize consistency, efficiency, and chemical quality.
Key Areas of Research and Findings
Propagation by Stem Cuttings
Cannabis is most commonly propagated via cuttings to maintain genetic uniformity and ensure consistent cannabinoid profiles. Caplan’s work offers some of the first peer-reviewed data on optimizing this method.
Findings:
Leaf count matters: Cuttings with three fully expanded leaves rooted significantly better than those with two.
Avoid leaf tip removal: Trimming leaf tips reduced rooting success—contrary to some common practices.
Cutting position is neutral: Whether cuttings were taken from the apical or basal part of the plant did not influence rooting performance.
Synthetic hormones outperform natural ones: A 0.2% indole-3-butyric acid (IBA) gel produced better rooting than a willow extract gel.
Takeaway: Small refinements in cutting practices significantly affect rooting rates and quality, making propagation more predictable and scalable.
Substrate and Organic Fertilizer Optimization
Caplan tested cannabis performance across two coir-based substrates with differing physical properties, and across a range of organic nitrogen concentrations.
Vegetative Stage:
Cannabis tolerated both tested substrates well, despite an ≈11% difference in container capacity.
No significant fertilizer–substrate interaction was observed during vegetative growth.
Increasing nitrogen concentration increased growth, but only up to a point—beyond which returns diminished.
Flowering Stage:
Substrate with lower container capacity (i.e., drier root zones) resulted in higher floral dry weight and, in some cases, higher cannabinoid concentrations (including THC).
Optimal fertilizer rates during flowering were substrate-specific.
Higher fertilizer levels increased yield but also diluted cannabinoid concentrations, revealing a trade-off between biomass and chemical quality.
Takeaway: Choosing the right substrate and dialing in nutrient rates specific to each growth phase is essential for balancing yield and potency.
Drought Stress Timing and Its Effects
One of Caplan’s most compelling contributions was his examination of controlled drought stress during flowering—a technique long rumored to “boost potency,” but rarely tested with rigor.
Findings:
When drought stress was introduced gradually over 11 days during week 7 of flowering, both THC concentration and cannabinoid yield per square meter increased.
A shorter drought stress of ≈8 days produced similar results to well-watered controls, indicating that timing and duration are critical.
Drought stress also influenced terpenoid profiles, showing promise for enhancing aromatic complexity.
Takeaway: Precision drought application late in flowering can be used as a tool to optimize secondary metabolite profiles, but only when applied under tightly controlled conditions.
Integrated Root Zone Management (IRM): The Core Framework
Throughout his work, Caplan used an IRM framework to study the interdependent nature of root zone variables—substrate type, water availability, nutrient concentrations, and gas exchange. Rather than isolating these factors, IRM treats them as a dynamic system requiring balance.
Examples of IRM in action:
Frequent irrigation can increase growth—but only if the substrate drains well and maintains oxygen availability.
High water-holding capacity substrates might reduce the need for frequent irrigation—but can lead to oxygen depletion and root stress.
Fertilizer concentration influences not only growth and yield, but also the electrical conductivity (EC) and pH of the root zone, which in turn affect nutrient uptake and microbial dynamics.
Takeaway: For senior growers seeking system-level control, IRM offers a scientifically grounded way to align growing conditions with plant needs throughout the production cycle.
Conclusion: Scientific Backbone for Commercial Cannabis Production
Dr. Caplan’s research brought rigor, reproducibility, and clarity to a field previously driven by tradition and guesswork. By identifying clear, testable parameters that affect rooting, vegetative development, flowering success, and cannabinoid profiles, his work has created a toolkit for modern cannabis producers.
Whether you're looking to increase yield, enhance potency, standardize propagation, or improve your root zone strategies, his data-driven approach provides the insight needed to refine your SOPs and drive performance across your operation.