Cold Stress and Chilling Injury
Identify how low tissue and root-zone temperatures alter membranes, metabolism, photosynthesis, water transport, and recovery in cannabis.
Identify how low tissue and root-zone temperatures alter membranes, metabolism, photosynthesis, water transport, and recovery in cannabis.
Core science
Cold slows enzyme activity, membrane transport, respiration, root growth, and water movement. Leaves may remain exposed to substantial light while carbon metabolism and repair slow, increasing photoinhibition risk. Chilled roots can restrict uptake even when air conditions appear acceptable.
Membrane lipids, genotype, prior acclimation, tissue age, duration, and rate of cooling influence injury. Symptoms can include slowed growth, drooping, discoloration, marginal injury, delayed rooting, and nutrient-like patterns. These signs are not unique and may appear after the cold event.
Night-time radiation, cold supply air, exterior surfaces, irrigation solution, outdoor transplant shock, and power failures can chill tissues below the room average. Condensation may accompany cooling when surfaces approach the dew point, adding disease risk to physiological stress.
Why this matters in cultivation
- Investigate minimum and duration, not only the daily average. Map cold surfaces and supply-air paths, measure root-zone and leaf temperature, and inspect equipment histories. During recovery, warm gradually and coordinate light so photosynthetic demand does not outrun repair.
- Distinguish chronic cool growth from an acute excursion. Record whether new growth resumes and whether reproductive development, roots, or specific canopy zones remain affected before deciding crop disposition.
Measure and record
Exposure
Minimum air, leaf, and root-zone temperature; duration; cooling and warming rate; and operating state.
Dew risk
RH, dew point, surface temperature, condensation, and wetness duration.
Plant response
Tissue and location, symptom onset, growth rate, water use, and root condition.
Recovery
Warming method, light adjustment, time to restored function, and residual injury.
Cause
Weather, HVAC, door, power, irrigation-temperature, or control-system event and CAPA.
Common misconceptions
Misconception: No frost means no cold injury
Correction: Chilling-sensitive function can decline above freezing.
Misconception: Purple tissue proves phosphorus deficiency
Correction: Genetics, cold, light, sugar status, and nutrient issues can overlap visually.
Misconception: Warm air immediately repairs chilled roots
Correction: Root-zone temperature and damaged physiology may recover more slowly.
Evidence limits and uncertainty
Cold tolerance differs widely among cannabis germplasm and developmental stages. Use facility-specific alarm limits based on measured crop response, not folklore labels such as indica or sativa.
Check your reasoning
- For "Cold Stress and Chilling Injury", explain the mechanism behind this objective: Identify how low tissue and root-zone temperatures alter membranes, metabolism, photosynthesis, water transport, and recovery in cannabis. Which observation or measurement would best test whether that mechanism is operating in the real crop?
- A learner claims, "No frost means no cold injury" Use the lesson’s science and evidence limits to explain why that claim is unreliable, then name one observation or measurement that could separate the competing explanations.
- Applied case — Investigate minimum and duration, not only the daily average. Map cold surfaces and supply-air paths, measure root-zone and leaf temperature, and inspect equipment histories. During recovery, warm gradually and coordinate light so photosynthetic demand does not outrun repair. Build a verification plan using the lesson’s record set (Exposure, Dew risk, Plant response). What would you compare before and after the action, and what result would make you revise the original interpretation?
Require lesson-specific evidence, not memorized universal targets. Open the rationales after you have written or discussed your own answer.
Answer rationale 1: Mechanism / workflow rationale
- A strong answer should connect the response to the lesson objective: Identify how low tissue and root-zone temperatures alter membranes, metabolism, photosynthesis, water transport, and recovery in cannabis.
- Cold slows enzyme activity, membrane transport, respiration, root growth, and water movement. Leaves may remain exposed to substantial light while carbon metabolism and repair slow, increasing photoinhibition risk. Chilled roots can restrict uptake even when air conditions appear acceptable.
- Membrane lipids, genotype, prior acclimation, tissue age, duration, and rate of cooling influence injury. Symptoms can include slowed growth, drooping, discoloration, marginal injury, delayed rooting, and nutrient-like patterns. These signs are not unique and may appear after the cold event.
- The most useful verification evidence includes Exposure: Minimum air, leaf, and root-zone temperature; duration; cooling and warming rate; and operating state.
- Keep this limit explicit: Cold tolerance differs widely among cannabis germplasm and developmental stages. Use facility-specific alarm limits based on measured crop response, not folklore labels such as indica or sativa.
Answer rationale 2: Misconception rationale
- The shortcut is unreliable because the lesson explicitly teaches a more conditional explanation.
- Representative misconception: No frost means no cold injury: Chilling-sensitive function can decline above freezing.
- Cold slows enzyme activity, membrane transport, respiration, root growth, and water movement. Leaves may remain exposed to substantial light while carbon metabolism and repair slow, increasing photoinhibition risk. Chilled roots can restrict uptake even when air conditions appear acceptable.
- A useful discriminator is Dew risk: RH, dew point, surface temperature, condensation, and wetness duration.
- Do not overextend the conclusion beyond this limit: Cold tolerance differs widely among cannabis germplasm and developmental stages. Use facility-specific alarm limits based on measured crop response, not folklore labels such as indica or sativa.
Answer rationale 3: Applied verification rationale
- In practice: Investigate minimum and duration, not only the daily average. Map cold surfaces and supply-air paths, measure root-zone and leaf temperature, and inspect equipment histories. During recovery, warm gradually and coordinate light so photosynthetic demand does not outrun repair.
- Record before action: Exposure: Minimum air, leaf, and root-zone temperature; duration; cooling and warming rate; and operating state.
- Also record: Dew risk: RH, dew point, surface temperature, condensation, and wetness duration.
- After the action, repeat the same measurement or observation so the comparison is valid.
- Revise the interpretation if the result conflicts with the lesson limit or the expected response: Cold tolerance differs widely among cannabis germplasm and developmental stages. Use facility-specific alarm limits based on measured crop response, not folklore labels such as indica or sativa.
Related lessons
Sources and evidence
- Nobel P.S. (2009). Physicochemical and Environmental Plant Physiology, 4th ed. Academic Press.
- THC Cannabis Plant Science Source Packet v1.1 (project source, May 2026).
- THC Cultivation SOP Source Materials Packet v1.0 (project source, May 2026).
Downloads
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