Contents
Temperature Effects
Temperature directly influences plant metabolism, photosynthesis rates, and transpiration. Understanding temperature patterns is critical for outdoor cannabis cultivation.
Optimal Temperature Ranges
| Growth Stage | Day Temperature (°C) | Night Temperature (°C) | Temperature Differential | Effects of Proper Range |
|---|
| Seedling | 20-25°C (68-77°F) | 18-22°C (65-72°F) | 2-3°C | Promotes strong root development and balanced growth |
| Vegetative | 22-28°C (72-82°F) | 18-22°C (65-72°F) | 3-6°C | Maximizes metabolic rate and photosynthesis |
| Early Flower | 20-26°C (68-79°F) | 16-20°C (61-68°F) | 4-6°C | Supports flower initiation and terpene retention |
| Late Flower | 18-24°C (65-75°F) | 15-18°C (59-65°F) | 3-6°C | Encourages resin production and terpene development |
Temperature Stress Thresholds
| Stress Type | Temperature Range | Duration | Plant Response | Mitigation Strategies |
|---|
| Cold Stress | 0-10°C (32-50°F) | >4 hours | Growth inhibition, purple stems/leaves, reduced metabolism | Wind blocks, thermal mass, row covers |
| Frost Damage | <0°C (32°F) | Any | Cellular damage, tissue death | Harvest before frost, greenhouse, frost covers |
| Heat Stress | 30-35°C (86-95°F) | >3 hours | Leaf curling, reduced photosynthesis, transpiration increase | Shade cloth, increased irrigation, misting |
| Critical Heat | >35°C (95°F) | >2 hours | Terpene volatilization, photosynthesis inhibition, reproductive issues | Moving plants, evaporative cooling, temporary greenhouses |
Growing Degree Days (GDD)
GDD is a measure of heat accumulation used to predict plant developmental rates and phenological stages.
Formula: GDD = [(Daily Max Temp + Daily Min Temp) ÷ 2] - Base Temp
For cannabis, use a base temperature of 10°C (50°F).
| Developmental Stage | Approximate GDD Required | Calculation Example |
|---|
| Germination to Seedling | 50-100 GDD | Day with 25°C max and 15°C min: [(25+15)÷2]-10 = 10 GDD |
| Seedling to Vegetative | 100-300 GDD | Accumulate daily calculations until target reached |
| Early to Mid Vegetative | 300-600 GDD | Track throughout season |
| Vegetative to Flowering | 600-1000 GDD | Will vary by latitude and variety |
| Flowering to Harvest | 1000-1500+ GDD | Total season requirements depend on strain |
Humidity Considerations
Relative humidity (RH) impacts transpiration rates, nutrient uptake, and susceptibility to pathogens.
Optimal Humidity Ranges
| Growth Stage | Optimal RH Range | VPD Range (kPa) | Risks Outside Range |
|---|
| Clones/Seedlings | 70-75% | 0.4-0.8 | Low: desiccation; High: damping off |
| Early Vegetative | 60-70% | 0.8-1.0 | Low: stunted growth; High: fungal issues |
| Late Vegetative | 50-60% | 1.0-1.2 | Low: nutrient issues; High: pathogen risk |
| Early Flower | 45-55% | 1.0-1.3 | Low: terpene loss; High: mold risk |
| Mid Flower | 40-50% | 1.1-1.4 | Low: reduced yield; High: bud rot |
| Late Flower | 35-45% | 1.2-1.6 | Low: premature drying; High: bud rot, mildew |
Vapor Pressure Deficit (VPD)
VPD measures the difference between the amount of moisture in the air and how much moisture the air can hold when saturated.
Interpreting VPD Values:
- <0.4 kPa: Extremely humid, high disease risk
- 0.4-0.8 kPa: Ideal for clones and seedlings
- 0.8-1.2 kPa: Optimal for vegetative growth
- 1.2-1.6 kPa: Optimal for flowering
- >1.6 kPa: Excessive transpiration, plant stress
Dew Point Assessment
Dew point is the temperature at which air becomes saturated and condensation forms. When plant tissue temperature falls below the dew point, moisture forms on plant surfaces, creating ideal conditions for fungal pathogens.
| Risk Level | Condition | Mitigation Strategies |
|---|
| High Risk | Nighttime temps within 2°C of dew point | Preventative fungicides, increase air circulation |
| Moderate Risk | Nighttime temps 2-5°C above dew point | Monitor closely, ensure good air movement |
| Low Risk | Nighttime temps >5°C above dew point | Standard cultural practices |
Light Intensity & Photoperiod
Light is both a source of energy for photosynthesis and a critical environmental signal that triggers developmental changes.
Seasonal Light Changes
| Season | Daylight Hours | Light Quality | Cultivation Considerations |
|---|
| Spring Equinox | 12 hours (increasing) | Moderate intensity, balanced spectrum | Good for germination and early vegetative growth |
| Summer Solstice | 14-16+ hours (latitude dependent) | High intensity, blue-dominant | Peak vegetative growth period |
| Fall Equinox | 12 hours (decreasing) | Moderate intensity, red-dominant | Natural flowering trigger for photoperiod varieties |
| Winter Solstice | 8-10 hours (latitude dependent) | Low intensity, red-dominant | Mostly dormant period for outdoor cultivation |
Daily Light Integral (DLI)
DLI measures the total amount of PAR (photosynthetically active radiation) received during a 24-hour period, measured in mol/m²/day.
| Growth Stage | Optimal DLI Range (mol/m²/day) | Plant Response | Expected at Latitude |
|---|
| Seedling | 10-20 | Balanced growth without stretching | Spring/Fall at 30-45° latitude |
| Vegetative | 20-30 | Robust growth, short internodes | Summer at 30-45° latitude |
| Flowering | 25-35 | Maximum yield potential | Late summer at 30-45° latitude |
| Late Flowering | 20-30 | Quality development | Early fall at 30-45° latitude |
Critical Photoperiod Thresholds
Cannabis is typically a short-day plant with critical photoperiod requirements for flowering:
| Cannabis Type | Flowering Trigger | Cultivation Implication |
|---|
| Photoperiod | <14 hours light (some strains <13 hours) | Plant during appropriate seasonal window for desired harvest timing |
| Autoflowering | Age-dependent (not photoperiod sensitive) | Can be planted throughout growing season where temperatures permit |
Wind & Air Movement
Wind affects plant development through mechanical stress, transpiration rates, and gas exchange efficiency.
Wind Speed Effects
| Wind Speed | Classification | Plant Effects | Cultivation Considerations |
|---|
| 0-5 km/h (0-3 mph) | Light Air | Minimal mechanical stress, potential for insufficient air exchange | May need supplemental fans outdoors in sheltered areas |
| 5-20 km/h (3-12 mph) | Light Breeze to Moderate Breeze | Positive mechanical stress (thigmomorphogenesis), good air exchange | Ideal range for plant development |
| 20-40 km/h (12-25 mph) | Fresh Breeze to Strong Breeze | Increased transpiration, mechanical stress | Consider windbreaks or plant training for resilience |
| >40 km/h (>25 mph) | Near Gale to Storm | Physical damage risk, excessive transpiration | Requires windbreaks or temporary protection |
Mechanics of Wind Training
| Wind Response | Physiological Change | Cultivation Benefit |
|---|
| Stem thickening | Increased ethylene production, enhanced lignification | Stronger plants, reduced lodging risk |
| Reduced height | Mechanical stress inhibits auxin transport | Shorter, more manageable plants |
| Increased root development | Compensatory response to above-ground stress | Improved drought tolerance, nutrient uptake |
Wind Risk Assessment
| Wind Type | Characteristics | Potential Damage | Preventive Measures |
|---|
| Prevailing Winds | Consistent direction, predictable | Long-term leaning, uneven canopy development | Strategic planting orientation, windbreaks on prevailing side |
| Gusting Winds | Sudden increases in speed | Branch breakage, particularly during flowering | Trellising, plant training, temporary shelters |
| Hot, Dry Winds | Low humidity, high temperature | Rapid dehydration, leaf burn | Increased irrigation, misting, windbreaks |
| Cold Winds | Rapid temperature drop | Stress response, slowed growth | Windbreaks, row covers, thermal mass |
Precipitation Patterns
Understanding rainfall patterns is essential for planning irrigation strategies and mitigating weather-related risks.
Rainfall Interpretation
| Weekly Rainfall | Classification | Irrigation Implication | Risk Assessment |
|---|
| <10 mm (<0.4") | Dry | Supplemental irrigation required | Drought stress, reduced growth |
| 10-25 mm (0.4-1") | Light | Reduced irrigation needed | Generally beneficial |
| 25-50 mm (1-2") | Moderate | Minimal irrigation needed | Low pathogen risk in well-drained soil |
| 50-100 mm (2-4") | Heavy | No irrigation needed, potential for excess | Moderate pathogen risk, soil erosion concern |
| >100 mm (>4") | Extreme | Drainage concerns | High pathogen risk, potential root damage |
Precipitation Timing Concerns
| Growth Stage | Precipitation Risk | Critical Considerations | Management Strategies |
|---|
| Seedling | Soil compaction, seedling damage | Delicate root systems vulnerable to waterlogging | Raised beds, temporary shelters |
| Vegetative | Foliar pathogens, stem breakage | Rapid growth can create dense canopy that traps moisture | Training for airflow, preventative treatments |
| Early Flower | Bud rot initiation, pollination disruption | Moisture entering developing buds | Defoliation of inner leaves, temporary rain shelters |
| Late Flower | Bud rot proliferation, reduced quality | Mature buds hold moisture, difficult to dry | Harvest before heavy rain events, permanent shelters |
Seasonal Precipitation Forecasting
Using historical data and seasonal forecasts to plan cultivation schedule:
| Season | Historical Pattern | El Niño Effect | La Niña Effect | Planning Strategy |
|---|
| Spring | [Regional data] | Often wetter | Often drier | Adjust planting dates based on forecast |
| Summer | [Regional data] | Variable by region | Variable by region | Plan irrigation systems based on historical data |
| Fall | [Regional data] | Often wetter | Often drier | Consider early harvest during wet El Niño forecasts |
| Winter | [Regional data] | Warmer, variable precipitation | Cooler, variable precipitation | Plan infrastructure improvements during off-season |
Seasonal Planning
Strategic planning based on seasonal weather patterns optimizes cultivation success.
Northern Hemisphere Cultivation Calendar
| Month | Average Conditions | Cultivation Activities | Weather-Related Concerns |
|---|
| January-February | Cold, short days | Indoor propagation, planning | Frost protection for greenhouse operations |
| March-April | Warming, increasing daylight | Hardening off, early planting | Late frost risk, wind protection |
| May-June | Warm, long days | Main season planting, vegetative growth | Spring storms, establishing irrigation |
| July-August | Hot, peak daylight | Robust vegetative growth, flowering begins | Heat stress, drought management |
| September-October | Cooling, decreasing daylight | Flowering, early harvests | Early frost risk, rain-related mold issues |
| November-December | Cold, short days | Final harvests, cleanup | Frost damage, winterization |
Southern Hemisphere Cultivation Calendar
| Month | Average Conditions | Cultivation Activities | Weather-Related Concerns |
|---|
| January-February | Hot, peak daylight | Robust vegetative growth, flowering begins | Heat stress, drought management |
| March-April | Cooling, decreasing daylight | Flowering, early harvests | Autumn rains, mold risk |
| May-June | Cold, shortening days | Final harvests, cleanup | Frost damage, winterization |
| July-August | Cold, short days | Indoor propagation, planning | Frost protection for greenhouse operations |
| September-October | Warming, increasing daylight | Hardening off, early planting | Late frost risk, wind protection |
| November-December | Warm, long days | Main season planting, vegetative growth | Spring storms, establishing irrigation |
Regional Climate Considerations
| Climate Zone | Characteristics | Cultivation Advantages | Challenges | Adaptation Strategies |
|---|
| Mediterranean | Hot, dry summers; mild, wet winters | Long growing season, low humidity during flower | Summer water stress | Drought-tolerant varieties, irrigation |
| Temperate | Moderate temps, year-round precipitation | Good natural water availability | Humidity-related pathogens | Greenhouse cultivation, mold-resistant strains |
| Continental | Hot summers, cold winters, seasonal precipitation | Distinct seasons support natural cycle | Short growing season | Light dep techniques, autoflowering varieties |
| Tropical/Subtropical | Warm year-round, wet/dry seasons | Year-round cultivation potential | High humidity, pest pressure | Sativa-dominant varieties, covered cultivation |
| Arid/Semi-arid | Hot days, cool nights, minimal precipitation | Low fungal pressure, quality potential | Water scarcity, heat stress | Water-efficient systems, shade structures |
Weather Risk Assessment
Proactive risk assessment allows for mitigation strategies before weather events impact crops.
Extreme Weather Preparedness
| Weather Event | Warning Signs | Potential Impact | Emergency Measures | Recovery Strategies |
|---|
| Hailstorm | Dark clouds, thunderstorm warnings | Physical damage to plants, broken branches | Temporary hail netting, movable plants indoors | Prune damaged material, apply protective sprays |
| Heavy Rain | Precipitation forecast >30mm/day | Soil erosion, flooding, pathogen outbreak | Temporary covers, trenches for drainage | Foliar fungicide, increase airflow, soil remediation |
| Heat Wave | Forecast temperatures >35°C for 3+ days | Heat stress, accelerated transpiration | Shade cloth (30-50%), increased irrigation | Foliar sprays, temporary reduction in nutrients |
| Cold Snap | Forecast temperatures <5°C | Growth stunting, potential frost damage | Row covers, cold frames, wind breaks | Stress recovery supplements, prune damaged tissue |
| High Winds | Wind advisories, approaching weather systems | Physical damage, increased transpiration | Temporary windbreaks, plant anchoring | Structural repairs, pruning, supplemental irrigation |
| Drought | Extended period without rainfall | Water stress, reduced growth/yield | Water conservation, mulching, irrigation | Gradual rehydration, stress recovery products |
Critical Timing Weather Risks
| Growth Stage | Most Significant Weather Risks | Impact on Crop | Monitoring Priority |
|---|
| Germination | Soil temperature fluctuations, excess moisture | Germination failure, damping off | Soil temperature, moisture levels |
| Early Vegetative | Late frost, wind damage to young plants | Stunted growth, physical damage | Frost warnings, wind forecasts |
| Late Vegetative | Heat stress, drought | Reduced growth rate, potential sex reversal | Temperature trends, soil moisture |
| Early Flowering | Temperature extremes, heavy rain | Flower formation issues, mold initiation | Day/night temperature differentials, rain forecasts |
| Mid Flowering | Rain events, humidity spikes | Bud rot, powdery mildew | Humidity levels, extended forecasts |
| Late Flowering | Early frost, fall rains | Reduced quality, harvest timing challenges | Frost warnings, precipitation forecasts |
Long-Term Climate Adaptations
| Climate Trend | Observed Changes | Cultivation Implications | Adaptation Strategies |
|---|
| Warming Temperatures | Earlier spring, later first frost | Longer potential growing season | Adjusted planting schedules, heat-tolerant varieties |
| Precipitation Changes | More intense rainfall events | Increased disease pressure, erosion | Improved drainage, protected cultivation |
| Increased Weather Variability | Unpredictable patterns | Planning uncertainty | Diversified growing methods, succession planting |
| Rising COâ‚‚ Levels | Enhanced plant growth potential | Changed plant development patterns | Adjusted nutrient ratios, cultivar selection |
Climate Data Resources
Weather Data Sources
| Resource Type | Examples | Data Provided | Application |
|---|
| Government Meteorological Services | NOAA, Met Office, BOM | Historical data, forecasts, climate norms | Long-term planning, seasonal strategies |
| Agricultural Extension Services | University extensions, USDA | Region-specific forecasts, growing degree days | Local cultivation recommendations |
| Weather Apps/Sites | Weather Underground, AccuWeather | Hyperlocal forecasts, historical comparisons | Day-to-day management decisions |
| On-Site Weather Stations | Davis Instruments, Ambient Weather | Real-time conditions, microclimate data | Precise monitoring, automation integration |
Key Data Points to Track
| Measurement | Frequency | Tools | Decision Support |
|---|
| Temperature (min/max) | Daily | Digital thermometers, weather stations | Growth rate expectations, stress management |
| Precipitation | Event-based | Rain gauges, weather stations | Irrigation planning, disease risk assessment |
| Humidity | Multiple times daily | Hygrometers, weather stations | Disease risk, transpiration management |
| Wind Speed/Direction | Daily | Anemometers, weather stations | Structure protection, plant training |
| Soil Temperature | Weekly | Soil thermometers | Planting timing, root development monitoring |
| Solar Radiation | Weekly averages | Pyranometers, light meters | Growth potential, supplemental lighting decisions |
CANNABIS CULTIVATION WEATHER LOG
Location: ________________ Week Beginning: ____________
DAILY MEASUREMENTS
-------------------------------------
| Date | Min | Max | Humidity | Precipitation | Wind | Notes |
| | °C | °C | % (am/pm)| mm | km/h | |
|------|-----|-----|----------|--------------|------|-------|
| | | | | | | |
| | | | | | | |
WEEKLY SUMMARY
-------------------------------------
GDD Accumulated: ________ Total Precipitation: ________mm
Notable Weather Events: _________________________________
Plant Response Observations: ____________________________
Adjustments Made: _____________________________________
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