VPD Chart and VPD Calculator in Celsius and Fahrenheit
Vapour Pressure Deficit, or VPD, is the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated. While VPD is often overlooked in indoor growing, this concept is critical because it affects how plants transpire and take up nutrients.
To have better control over the environment, A VPD chart clearly represents the relationship between temperature, humidity, and vapor pressure. By recommending the ideal ranges for different stages of weed growth, a VPD chart is a reliable reference for achieving optimal yields when cultivating marijuana indoors. Fortunately, we’ve done the work for you. Plus, we have an online Room and Leaf Vapor Pressure Calculator.
Understanding VPD and LVPD
Let’s break it into detail. VPD measures the air's drying power on plants, indicating how much moisture the atmosphere extracts from them. Essentially, it reflects the moisture being drawn out from the plant by the surrounding air.
Why does VPD matter? Plants rely on transpiration to grow, similar to how humans sweat. Through their stomata, akin to human pores, plants release moisture to pull in more liquids through their roots, which fuels photosynthesis. If VPD is too high, plants cannot meet the environmental demands placed on them, causing the air to dry them out too quickly. This results in symptoms similar to nutrient deficiencies and stunted growth.
Conversely, if VPD is too low, plants cannot transpire effectively. Excess moisture may accumulate on the leaves, slowing plant growth and potentially leading to moldy weed and fungal attacks.
However, plant's experience differs slightly as their temperature is usually cooler than the room temperature due to transpiration. This is where the Leaf Vapor Pressure Deficit (LVPD) comes into play. If the plant and room temperatures are identical, their VPD levels match. Usually, leaves are 3° to 5° F cooler than the room because transpiration cools them.
By far, you probably know that while the room's VPD is important, what to really focus on is the LVPD. By understanding the cannabis plant's internal VPD, you stand a chance for the best and largest cannabis harvests.
Here’s an online room and Leaf Vapor Pressure Calculator:
VPD Charts for Veg/Flower in Celsius and Fahrenheit
To calculate the appropriate VPD, you need to consider the weed plant growth stage. In the clone or baby stage, for example, plants are quite fragile and can't handle much stress. Therefore, it's best to maintain a VPD range of around 0.4 – 0.8 kPa during this stage. As cannabis plants enter the vegetative stage, they become more robust and can tolerate higher VPD levels. During the flowering stage, plants can handle even higher VPD.
Plant Cycle Stage VPD Chart
| Plant Cycle Stage | Min Leaf VPD | Max Leaf VPD | Temperature | Relative Humidity |
|---|---|---|---|---|
| Propagation / Early Veg | 0.8 kPa | 1.0 kPa | 70° F | 60% |
| Late Veg / Early Flower | 1.0 kPa | 1.2 kPa | 75° F | 50% |
| Mid / Late Flower | 1.2 kPa | 1.6 kPa | 75° F | 40% |
We’ll provide you with the most comprehensive set of VPD charts tailored for the vegetative and flowering stages in both Celsius and Fahrenheit, allowing you to simply take your measurements and refer to the appropriate color-coded VPD chart adjusted for leaf temperature. By referring to these charts, you can ensure that your plants are growing in the best possible conditions for each growth stage.
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