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How Vapor Pressure Deficit Impacts Cannabis Plants

How Vapor Pressure Deficit Impacts Cannabis Plants Professor DeBacco Vapor Pressure Deficit (VPD) This is an advanced method for understanding and measuring the indoor (or technically outdoor) growing environment. Outdoor it is more for monitoring Indoor growers can calculate VPD and then made changes to the conditions It does require more equipment to gather information and an understanding of the overall growing environment which is why this is considered to be a more advanced technique. Equipment Needed Thermometer Used to measure the air temperature Hygrometer Allows the humidity to be measured IR thermometer Provides the temperature of the leaf With the data generated you can calculate the VPD of the growing space. VPD Takes Into Account Entire Environment This allows a consistent measure that takes into account the three main variables in a grow space. What VPD Influences Transpiration As VPD increases, the plant transpires faster Stomata Opening As VPD increases, stomata get smaller. CO2 uptake As VPD increases and stomata get smaller, CO2 uptake gets reduced. Nutrient intake at the roots Increasing VPD and transpiration rates will mean the roots pull in more nutrients. Plant stress Increasing VPD = Increased plant stress VPD Chart Vapor Pressure Conversion Factors The most common unit of measure for growers is kilopascals (kPa), however inches of Mercury (in Hg) can also be used. Some Suggested Target VPD by Growth Phase Propagation and early Veg: 0.2 – 0.8 kPa Late veg and early Flower: 0.8 – 1.4 kPa Mid-flower to late Flower: 1.2 – 1.5 kPa How Environment Impacts VPD Temperature Increase temperature : Increase VPD Decrease temperature : Decrease VPD Humidity Increase humidity : Decrease VPD Decrease humidity : Increase VPD Light Intensity Increase light intensity : increase leaf temps = Increase VPD Decrease light intensity : decrease leaf temps = Decrease VPD Relative Humidity at Given Temperatures and VPDs Suggested values are for required to maintain ideal growing conditions. This is the lights on Transpiration = Water Movement in Plants Water first enters the roots of a plant and will travel through the plant and exit out small regulated pores called stomata. This general movement of water is called transpiration is it allows for nutrients to move through the plant and also is a method of cooling the plant. The humidity is considered to be around 100% inside a healthy leaf. This represents saturated vapor pressure Transpiration Rates Transpiration rates will be faster in hot and dry conditions Rates will slow in high humid because the water has no where to evaporate to. The stomata need to be regulated because when they are open they can let CO2 in for photosynthesis but at the same time the plant is loosing water. Plants need to balance out the ability to photosynthesize and remain hydrated. Link to Lecture Slides: https://drive.google.com/file/d/1GfAU... *Due to the description character limit the full work cited for "How Vapor Pressure Deficit Impacts Cannabis Plants" can be viewed at... https://drive.google.com/file/d/1h1BG...