Plant hormones orchestrate every aspect of cannabis growth and development, from seed germination to flower maturation. Understanding how these chemical messengers work explains why training techniques succeed or fail, and helps growers make informed decisions about plant manipulation. This article explores the major plant hormones affecting cannabis cultivation and debunks common misconceptions about training and growth regulation.

Hormone Fundamentals

What Plant Hormones Actually Are

Plant hormones are chemical signaling molecules that coordinate growth, development, and responses to environmental stimuli. Unlike animal hormones, plant hormones often work in complex interactions rather than simple cause-and-effect relationships. The same hormone can have different effects depending on concentration, location, and the presence of other hormones.

Cannabis produces and responds to five major hormone classes: auxins, cytokinins, gibberellins, abscisic acid, and ethylene. Each class includes multiple related compounds with overlapping but distinct functions. Understanding these interactions helps predict plant responses to training and environmental changes.

Myth Debunked: Plant hormones don’t work like switches that turn growth “on” or “off.” They function more like a complex orchestra, with multiple hormones interacting to produce coordinated responses. This complexity explains why simple training rules often fail in practice.

Auxins and Apical Dominance

Auxin Transport and Distribution

Auxins, primarily indole-3-acetic acid (IAA), are produced in shoot tips and young leaves, then transported downward through the plant. This polar transport creates concentration gradients that influence cell elongation, root development, and branching patterns.

Apical dominance results from auxin produced in the terminal bud inhibiting lateral bud growth. When auxin levels decrease—either through distance from the source or removal of the terminal bud—lateral buds become active and begin growing.

Training Technique Mechanisms

Low Stress Training (LST) works by changing auxin distribution without removing tissue. Bending the main stem horizontally redistributes auxin flow, reducing apical dominance and allowing lateral branches to develop more vigorously.

Topping removes the primary auxin source, immediately releasing lateral buds from inhibition. However, the plant must redirect energy to establish new growing points, temporarily slowing overall growth while new leaders develop.

Myth Debunked: “Stress makes plants stronger” oversimplifies hormone responses. Training techniques work by manipulating hormone distribution, not by creating beneficial stress. Excessive or poorly timed training can disrupt hormone balance and reduce plant performance.

Root Development Regulation

Auxins promote root initiation and development, explaining why rooting hormones contain synthetic auxins. However, optimal auxin concentrations for rooting are much lower than those found in shoot tips, illustrating the importance of concentration-dependent responses.

Cannabis clones root best when auxin levels are sufficient to stimulate root initiation but not so high as to inhibit root elongation. This balance explains why taking cuttings from actively growing but not overly vigorous shoots typically produces better rooting success.

Cytokinins and Cell Division

Cytokinin Functions and Sources

Cytokinins promote cell division and are primarily produced in root tips and developing seeds. They work antagonistically with auxins—high cytokinin:auxin ratios promote shoot development, while high auxin:cytokinin ratios favor root growth.

In cannabis cultivation, cytokinin activity affects branching patterns, leaf development, and aging processes. Understanding cytokinin function helps explain why root health directly impacts shoot growth and why stressed root systems produce poor vegetative growth.

Branching and Bud Development

Cytokinins overcome auxin-mediated apical dominance by promoting lateral bud growth. This interaction explains why healthy root systems support more vigorous branching and why root damage reduces lateral growth even when shoot tips are removed.

Training techniques that improve light exposure to lateral buds may increase local cytokinin activity, enhancing branch development. However, the primary effect still comes from altered auxin distribution rather than direct cytokinin manipulation.

Leaf Senescence and Nutrient Mobility

Cytokinins delay leaf senescence and maintain photosynthetic capacity. As cytokinin production decreases with age or stress, older leaves begin senescing and translocating nutrients to younger tissues or developing flowers.

This process explains the natural yellowing of lower leaves during flowering—it’s not necessarily a nutrient deficiency but a programmed response to changing hormone levels and resource allocation priorities.

Gibberellins and Stem Elongation

Gibberellin Effects on Growth

Gibberellins promote stem elongation, leaf expansion, and flowering in some plants. Cannabis produces multiple gibberellins that affect different aspects of growth and development, with effects varying by concentration and plant development stage.

High gibberellin activity produces tall, stretched plants with long internodes, while low activity results in compact, bushy growth. Environmental factors like light quality and temperature influence gibberellin synthesis and activity.

Environmental Interactions

Red light promotes gibberellin synthesis, while blue light inhibits it. This explains why plants grown under red-heavy light sources tend to stretch, while those under blue-rich lighting remain more compact.

Temperature also affects gibberellin activity—cooler temperatures generally reduce gibberellin effectiveness, leading to more compact growth. Understanding these relationships helps predict plant responses to environmental changes.

Myth Debunked: Stretching isn’t always bad or always good. Moderate stem elongation can improve light penetration and air circulation, while excessive stretching wastes energy and creates structural problems. The goal is appropriate elongation for the growing situation.

Flowering and Sex Expression

Gibberellins can influence sex expression in cannabis, with high levels potentially promoting male flower development even in genetically female plants. This effect is more pronounced under stress conditions that alter normal hormone balance.

Environmental stresses that affect gibberellin levels—including light stress, temperature extremes, and nutrient imbalances—may increase hermaphroditism risk. Maintaining stable growing conditions helps preserve normal hormone balance and reduces unwanted sex expression changes.

Abscisic Acid and Stress Responses

Stress Hormone Functions

Abscisic acid (ABA) coordinates plant responses to environmental stresses including drought, high temperature, and high salinity. ABA triggers stomatal closure, promotes root growth, and activates stress-protective mechanisms.

During water stress, ABA accumulation causes stomata to close, reducing water loss but also limiting CO₂ uptake for photosynthesis. This trade-off explains why stressed plants often show reduced growth even when other resources are adequate.

Dormancy and Germination

ABA maintains seed dormancy and prevents premature germination under unfavorable conditions. Gibberellins counteract ABA effects, promoting germination when conditions improve. This hormone balance explains why some cannabis seeds require specific treatments to achieve consistent germination.

Environmental factors during seed development affect ABA content and dormancy depth. Seeds produced under stress conditions often have higher ABA levels and may require longer or more intensive treatments to break dormancy.

Ethylene and Senescence

Ethylene Production and Effects

Ethylene is a gaseous hormone that promotes fruit ripening, flower senescence, and stress responses. Cannabis produces ethylene in response to physical damage, pathogen attack, and environmental stresses.

High ethylene levels can accelerate flower maturation but may also promote premature senescence and reduce final yield. Understanding ethylene effects helps explain why stressed plants often finish earlier but with lower quality and quantity.

Training-Induced Ethylene

Physical manipulation during training can stimulate ethylene production, potentially affecting plant development. Gentle, gradual training minimizes ethylene production, while aggressive or sudden manipulation can trigger stress responses that reduce growth.

This explains why LST techniques that gradually bend stems over several days typically produce better results than sudden, severe bending. The plant has time to adjust hormone levels without triggering major stress responses.

Hormone Interactions in Practice

Integrated Hormone Management

Successful cannabis cultivation requires understanding that hormones work together, not independently. Training decisions, environmental management, and cultural practices all affect multiple hormone systems simultaneously.

For example, topping removes auxin sources but may also trigger ethylene production and alter cytokinin distribution. The net effect depends on plant health, environmental conditions, and timing relative to other stresses.

Timing Considerations

Hormone sensitivity varies throughout plant development. Young, actively growing plants typically respond more dramatically to training than older, established plants. Similarly, plants under stress may respond differently than healthy, vigorous plants.

Understanding developmental timing helps optimize training effectiveness while minimizing negative impacts. Major training should generally occur during active vegetative growth when plants can quickly recover and establish new growth patterns.

Environmental Hormone Regulation

Light Quality Effects

Light spectrum directly affects hormone synthesis and activity. Red light promotes auxin and gibberellin production, encouraging stem elongation. Blue light enhances cytokinin activity and promotes compact, bushy growth.

Far-red light can trigger shade avoidance responses mediated by phytochrome, leading to increased stem elongation and altered branching patterns. Understanding these responses helps explain plant behavior under different lighting conditions.

Temperature and Hormone Activity

Temperature affects hormone synthesis, transport, and activity. Cool temperatures generally slow hormone-mediated processes, while warm temperatures accelerate them. Extreme temperatures can disrupt normal hormone balance and trigger stress responses.

This temperature sensitivity explains why training responses vary seasonally in outdoor cultivation and why indoor environmental control improves training predictability.

Practical Training Applications

LST Technique Optimization

Effective LST manipulates auxin distribution while minimizing stress hormone production. Begin training when plants are actively growing and healthy. Use gentle pressure applied gradually over several days rather than sudden, severe bending.

Monitor plant responses and adjust techniques based on observed hormone-mediated changes. Healthy plants should show increased lateral growth within 3-5 days of effective LST application.

Topping and Recovery

Topping creates a temporary hormone imbalance that requires recovery time. Plan topping to allow adequate recovery before flowering initiation. Healthy plants typically require 7-14 days to fully recover and establish new growth patterns.

Avoid topping stressed plants or during environmental extremes when hormone systems are already disrupted. Multiple toppings should be spaced to allow complete recovery between interventions.

SCROG Implementation

Screen of Green (SCROG) techniques work by maintaining multiple growing points at similar heights, preventing any single shoot from establishing strong apical dominance. This requires understanding how auxin distribution affects competitive relationships between branches.

Effective SCROG management involves continuous minor adjustments to maintain hormone balance across multiple growing points rather than major periodic interventions.

Common Training Mistakes

Over-Manipulation

Excessive training can disrupt hormone balance and trigger chronic stress responses. Plants have limited capacity to respond to manipulation—exceeding this capacity reduces rather than improves performance.

Myth Debunked: “More training always means more yield” is false. Optimal training involves finding the right balance between manipulation and allowing natural hormone-regulated growth. Over-trained plants often produce less than appropriately trained ones.

Poor Timing

Training during flowering disrupts hormone systems when plants are focused on reproductive development. Late-stage training can reduce flower development and final yield quality.

Similarly, training stressed or unhealthy plants compounds existing hormone imbalances and may prevent recovery. Always ensure plants are healthy and actively growing before implementing training techniques.

Ignoring Recovery Time

Each training intervention requires recovery time for hormone systems to reestablish balance. Continuous manipulation prevents this recovery and can lead to chronic stress responses.

Plan training schedules to allow adequate recovery between interventions. Monitor plant responses and adjust timing based on observed recovery rates rather than rigid schedules.

Resources

1. Taiz, L., Zeiger, E., Møller, I. M., & Murphy, A. (2015). Plant Physiology and Development (6th ed.). Sinauer Associates. ISBN: 978-1605353531

2. Davies, P. J. (Ed.). (2010). Plant Hormones: Biosynthesis, Signal Transduction, Action! (3rd ed.). Springer. ISBN: 978-1402026850

3. Santner, A., Calderon-Villalobos, L. I., & Estelle, M. (2009). Plant hormones are versatile chemical regulators of plant growth. Nature Chemical Biology, 5(5), 301-307. DOI: 10.1038/nchembio.165

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5. Chandra, S., Lata, H., & ElSohly, M. A. (2017). Propagation of cannabis for clinical research: An approach towards a modern herbal medicinal product. Frontiers in Plant Science, 8, 958. DOI: 10.3389/fpls.2017.00958

6. Mohan Ram, H. Y., & Sett, R. (1982). Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics, 62(4), 369-375. DOI: 10.1007/BF00275107

7. Persans, M. W., Nieman, R., & Spalding, E. P. (2022). Apical dominance in Cannabis sativa is regulated by the BRANCHED1 transcription factor. Planta, 255(4), 1-12. DOI: 10.1007/s00425-022-03859-7

8. Burgel, L., Hartung, J., Pflugfelder, A., & Graeff-Hönninger, S. (2020). Impact of different phytohormones on morphology, yield and cannabinoid content of Cannabis sativa L. Plants, 9(6), 725. DOI: 10.3390/plants9060725

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[This post assumes legal hemp/cannabis breeding in compliance with all applicable laws and regulations.]