Water & Environment
Plant water relations, transpiration, humidity, VPD, temperature, airflow, environmental stress, and climate control.
Published lessons
These pages are organized here by subject. The permanent THC-ENC IDs remain stable behind the scenes even when a clearer display title is used.
Water Potential and the Soil-Plant-Atmosphere Continuum
Explain water movement through substrate, roots, xylem, leaves, and air using water-potential gradients rather than the vague idea that roots simply pull water upward.
Transpiration as a Physical and Biological Process
Separate the physical diffusion of water vapor from the biological controls that regulate stomata, leaf temperature, and whole-canopy water loss.
Relative Humidity, Dew Point, and Condensation
Use relative humidity and dew point correctly to identify condensation risk on leaves, walls, ducts, and other crop-space surfaces.
Saturation Vapor Pressure and Temperature
Calculate saturation vapor pressure consistently and explain why temperature errors change RH, dew-point, and VPD interpretations.
Vapor Pressure Deficit: Meaning and Calculation
Calculate air VPD and interpret it as one atmospheric driver of water loss rather than a universal crop prescription.
Air VPD Versus Leaf VPD
Calculate leaf-to-air VPD using measured leaf temperature and explain when it differs materially from air VPD.
Leaf Temperature Measurement
Collect defensible leaf-temperature data with infrared or contact methods and avoid common targeting, emissivity, and reflection errors.
Boundary Layers and Air Movement
Explain how leaf size, surface structure, canopy density, and air speed alter heat and vapor exchange at the leaf surface.
Canopy Microclimates and Dead Zones
Map spatial and temporal differences in temperature, humidity, leaf temperature, airflow, and CO2 within a crop canopy.
Root-Zone Moisture and Plant Water Status
Relate substrate water content, matric potential, salinity, root oxygen, and plant demand without treating one moisture reading as a complete diagnosis.
Irrigation Volume, Frequency, and Distribution Uniformity
Design and verify irrigation events by separating dose, timing, root-zone storage, drainage, and delivery uniformity.
Dryback: Measurement, Interpretation, and Limits
Define dryback with explicit units and reference points, then interpret the change without turning an industry shorthand into a universal plant target.
Runoff, Leaching Fraction, and Salt Movement
Measure drainage and leaching consistently and interpret runoff EC as a method-dependent indicator rather than a direct sample of the entire root zone.
Drought Stress and Recovery
Recognize progressive water-deficit responses, distinguish reversible regulation from injury, and evaluate recovery with plant and root-zone measurements.
Overwatering, Hypoxia, and Root Decline
Explain how excessive water-filled pore space and poor drainage restrict root respiration and increase the risk of secondary root decline.
Heat Stress and Cooling Responses
Separate warm growth conditions from heat stress and evaluate leaf energy balance, root-zone temperature, and recovery before assigning setpoints.
Cold Stress and Chilling Injury
Identify how low tissue and root-zone temperatures alter membranes, metabolism, photosynthesis, water transport, and recovery in cannabis.
Carbon Dioxide Supply, Ventilation, and Enrichment Context
Manage CO2 as a measured photosynthetic input and occupational hazard, coordinated with light, ventilation, crop demand, and fail-safe controls.
Sensor Placement, Mapping, and Calibration
Build a traceable environmental measurement system that distinguishes representative control sensors, diagnostic mapping instruments, and independent safety devices.
Stage-Aware Environmental Setpoints and Risk Review
Build environmental control envelopes from plant stage, measured tissue conditions, facility capability, and documented risk instead of copying a universal chart.