Crop steering is a cannabis cultivation technique where careful control over environmental factors guides plant growth, optimizes yields and enhances quality. By adjusting elements like light intensity, irrigation, temperature, humidity and root zone conditions, growers can steer plants toward vegetative growth—channeling energy and resources on foliage, stems and roots—or generative growth, also known as flowering or reproductive growth.
This blog post explains how crop steering works and how different environmental controls can steer crops toward one type of growth over the other.
How crop steering works
Plants produce hormones that regulate growth, flowering and stress responses, and these hormonal pathways are influenced by environmental conditions. When plants experience mild stress like reduced water availability, their hormone response shifts to prioritize reproduction, a critical phase for flowering plants like cannabis. Moderate drought even stimulates secondary metabolite production.[1] In stress-free environments, hormonal signals continue to promote vegetative growth.
Crop steering manipulates the environment and root zone to induce those metabolic and hormonal changes. By fostering a stress-free environment, growers can steer cannabis toward vegetative growth, which encourages leaf and stem development. By replicating natural stressors like drought, growers can steer a cannabis plant toward generative growth, which focuses on flowering reproduction. Irrigation and environmental control are the pillars of crop steering.
Crop steering through irrigation
Water availability is the main stressor leveraged in crop steering. By adjusting irrigation frequency, volume and timing, growers can drive either vegetative or generative growth. Specifically, growers can stress the crop through water potential, which refers to how easily water moves. Since water moves from areas of high to low potential, plants can absorb water more easily when the water potential is low.
Two types of water potential influence water’s movement from the growing medium to the roots: matric and osmotic. Matric refers to how well the growing medium holds water; while osmotic refers to how solute concentrations like nutrients influence water movement. When fertilizer salts are dissolved in a nutrient solution, they become available in their charged ionic forms and attract water molecules, so water can’t move as freely. As the growing medium dries out, both matric and osmotic potential rise, making it harder for the roots to absorb water.
The balance between matric and osmotic potential regulates water and nutrient uptake. Since higher osmotic potential means less free water available for absorption, it helps draw water out of plants. A lower matric potential means water is not as bound to the growing medium—and therefore more available for absorption, encouraging vegetative growth.
Water availability is the main stressor leveraged in crop steering. By adjusting irrigation frequency, volume and timing, growers can drive either vegetative or generative growth. Specifically, growers can stress the crop through water potential, which refers to how easily water moves. Since water moves from areas of high to low potential, plants can absorb water more easily when the water potential is low.
Two types of water potential influence water’s movement from the growing medium to the roots: matric and osmotic. Matric refers to how well the growing medium holds water; while osmotic refers to how solute concentrations like nutrients influence water movement. When fertilizer salts are dissolved in a nutrient solution, they become available in their charged ionic forms and attract water molecules, so water can’t move as freely. As the growing medium dries out, both matric and osmotic potential rise, making it harder for the roots to absorb water.
The balance between matric and osmotic potential regulates water and nutrient uptake. Since higher osmotic potential means less free water available for absorption, it helps draw water out of plants. A lower matric potential means water is not as bound to the growing medium—and therefore more available for absorption, encouraging vegetative growth.
Managing the root zone
Because matric and osmotic potentials directly influence water absorption, root zone management is essential for crop steering.
The root zone’s water content—the percentage of total water volume a container holds when saturated—decreases after irrigation due to runoff, evaporation and root uptake, a process called “dry down” or “dry back.” As the growing medium dries, matric potential increases, steering crops toward generative growth.
Similarly, as the growing medium dries out, the root zone’s electroconductivity (EC) increases. EC measures total salt concentration, and as water content decreases, the fertilizer salts that remain in the root zone increase osmotic potential.[2] This makes it harder for crops to absorb water, steering them toward generative growth.
Maintaining the right water content and EC in the root zone through irrigation therefore helps steer the crop toward either vegetative or generative growth. A higher water content and lower EC supports vegetative growth, while a drier growing medium and higher EC support generative growth.
Balancing other environmental factors
In addition to water and root zone management, several other environmental factors influence plant development and water uptake:
- Temperature, both air and leaf, affects growth rates. Cannabis thrives in the upper 70s°F unless it is supplemented with supplemental CO2, which raises the ideal range to the mid-80s°F. Air temperature may differ from leaf temperature due to airflow, light intensity or humidity.
- Carbon dioxide (CO2), along with light and water, is essential for photosynthesis. Even if other environmental factors are optimal, and plants are well-nourished, without sufficient CO2 they cannot reach their maximum growth potential.
- Relative humidity helps regulate evaporation and transpiration. High humidity prevents plants from transpiring, slowing water and nutrient uptake. Low humidity induces plants to transpire excessively; the stomata close, also reducing nutrient uptake. The latter is more likely to happen under intense lighting.
- Light intensity, measured in photosynthetic photon flux density (PPFD), also influences the transpiration rate. Cannabis yields rise linearly with PPFDs up to 1,400 μmol/m²/s.[3] However, excessive light should be avoided in the early growth stages to prevent light stress or damage to chlorophyll pigments. Gradually increase light intensity as plants mature, so they can effectively utilize the excess energy for photosynthesis.
- Vapor pressure deficit (VPD) provides insight into how efficiently plants can transpire. Whether you want to steer the crop toward vegetative or generative growth determines what the ideal VPD should be. VPD is influenced by temperature and humidity, and a simple VPD chart shows whether VPD is in the ideal range.
Steering vegetative growth
Cannabis plants go through three phases in their life cycle: germination, vegetative and flowering. During the “veg” phase, they establish their structure and devote energy toward growing foliage, stems and roots to capture critical resources like nutrients, water and light. Steering plants toward vegetative growth helps them to continue in this development.
Since plants switch to generative or reproductive growth when they experience stress, the key to vegetative steering is creating a stress-free environment. That means ensuring a higher water content level and lower EC through frequent, longer irrigation, which lowers both the matric and osmotic water potential, so plants do not sense water scarcity.
Maintaining a warmer air temperature along with higher humidity will also keep the VPD lower, reducing transpiration, which is optimal for vegetative growth. Since high light intensity also causes higher transpiration rates, which can lead to drought stress, light intensity should be kept low to moderate. For the veg phase, low light intensity should be around 100–200 μmol/m²/s and moderate around 200–400 μmol/m²/s, depending on the early or late growth phase.
Parameters
Ideal range
Temperature
78‒85oF
RH
70‒80%
VPD
0.6‒1.1 kpa
CO2
600‒1000 ppm
Day/night differential temperature
0‒10oF
Dry back
1‒10%
Substrate temperature
74‒78oF
EC
2‒4 ds/m
VWC
40‒50%
Ramp-up irrigation[4]
7‒59
Table 1. Vegetative steering recommendations from Growlink. Source: Baldinger, Marcus and Kevin Crouch. “Crop Steering: A Comprehensive Guide by Growlink.” Accessed November 10, 2024. https://www.scribd.com/document/698710862/Growlink-E-Book-Crop-Steering-V1-3.
Steering generative growth
The key to steering crops toward generative growth is to put them under mild stress. Make plants believe that they are fighting for survival, so they direct their energy toward reproduction (i.e., buds). We agree with Growlink’s recommendations that the best time to steer generatively is the early flowering phase, as it encourages more pre-flowers.[5]
Increasing VPD and light intensity raises the transpiration rate, releasing more water and reducing the growing medium’s water content. Keep an eye on the temperature; it may need to be lowered to remain within the ideal range under higher light intensity.
Lowering the water content of the growing medium also causes the EC to rise, increasing the matric and osmotic water potential and making absorption harder. This combination of greater transpiration and less water absorption simulates sufficient drought stress to steer generative growth.
Parameters
Ideal range
Temperature
65‒78oF
RH
45‒60%
VPD
1.0‒1.5 kpa
CO2
1000‒1500 ppm
Day/night differential temperature
0‒10oF
Dry back
15‒30%
Substrate temperature
74‒78oF
EC
5‒12 ds/m
VWC
35‒60%
Ramp-up irrigation
5‒7%
Table 2. Generative steering recommendations from Growlink. Source: Baldinger, Marcus and Kevin Crouch. “Crop Steering: A Comprehensive Guide by Growlink.” Accessed November 10, 2024. https://www.scribd.com/document/698710862/Growlink-E-Book-Crop-Steering-V1-3.
Precision for higher payoff
Crop steering is a management-intensive approach to cannabis cultivation. Creating and maintaining a crop steering schedule that triggers plant hormones and alters plant growth requires significant precision. Automated irrigation systems are integral to crop steering efforts, allowing growers to manage nutrient dosing, irrigation frequency and water content with greater accuracy.
By mastering crop steering techniques, cannabis growers can stay ahead in an increasingly competitive industry where yield and quality consistency is king. Growers need to understand how factors like irrigation, light, temperature, and humidity influence vegetative and generative growth if they want to optimize their operations for higher yields, improved quality and greater profitability.
Emerald Harvest Team
[1] Caplan, Deron. 2021. “3 Tips for Controlled Drought Stress.” Cannabis Business Times, May 26. https://www.cannabisbusinesstimes.com/irrigation/article/15690170/3-tips-for-controlled-drought-stress.
[2] Klaassen, Pieter. 2012. “Electrical Conductivity, why it matters.” CANNA, June 5. https://www.canna-uk.com/articles/electrical-conductivity-why-it-matters.
[3] Rodriguez-Morrison, Victoria et al. “Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment.” Frontiers in plant science vol. 12 646020. 11 May. 2021, doi:10.3389/fpls.2021.646020.
[4] Ramp-up irrigation involves turning pumps on and off to achieve specific irrigation rates.
[5] Baldinger, Marcus and Kevin Crouch. “Crop Steering: A Comprehensive Guide by Growlink.” Accessed November 10, 2024. https://www.scribd.com/document/698710862/Growlink-E-Book-Crop-Steering-V1-3