In professional cannabis cultivation, precise environmental control is crucial for maximum yields. An often underestimated but hugely important factor is vapor pressure deficit (VPD) . The VPD chart is your key to determining the optimal humidity and temperature for each growth stage of your plants. This article explains what VPD is, its importance for cannabis cultivation, and how to effectively use the VPD chart to optimize your harvests.
What is Vapor Pressure Deficit (VPD)?
The VPD measures the difference between the current humidity in the air and the maximum possible humidity at a given temperature. Simply put, it's the air's "capacity" to absorb water from the plant. An incorrect VPD value can stress the plant and disrupt its water balance, leading to stunted growth, stress, and disease. Optimal VPD values, on the other hand, promote the efficient uptake of water and nutrients, resulting in vigorous growth and higher yields.
Why is VPD so important in cannabis cultivation?
- Optimal water uptake: An ideal VPD value allows the plant to efficiently absorb water from the substrate. Excessive humidity inhibits transpiration and thus water uptake, while too low humidity can lead to excessive transpiration and dehydration.
- Increased growth: With optimal VPD, the plant can photosynthesize more efficiently, resulting in faster growth and larger harvests.
- Mold prevention: A correctly adjusted VPD helps maintain humidity levels at a level that prevents mold and mildew growth.
- Stress reduction: Plants growing in an optimal VPD range are healthier and more resistant to stress factors.
How do you read the VPD table?
The VPD table shows the VPD value (in kilopascals, kPa) as a function of air temperature (°C) and relative humidity (%). Different growth phases require different optimal VPD ranges.
- Vegetative phase: Here a lower VPD value is better because the plants need more moisture for strong leaf and root growth.
- Flowering phase: During flowering, the VPD value should be slightly higher to promote flower growth and prevent mold.
Complete VPD table for cannabis cultivation
How to use the VPD table (with leaf temperature measurement):
For optimal VPD detection, it is ideal to consider the leaf temperature of the plants, as this often differs slightly from the ambient air temperature.
-
Measure:
- Use a hygrometer to accurately measure the relative humidity in your grow room.
- Measure the air temperature with a conventional thermometer.
- Use a laser thermometer to measure the temperature of your plants' leaf surfaces. Point the laser beam at the underside of a healthy, fully developed leaf for the most accurate measurement.
-
Use a VPD calculator: Instead of using the table directly with the air temperature, use a VPD calculator . You can find such a calculator on Misch-Shop.de VPD calculator These calculators allow you to enter leaf temperature and humidity to determine a more precise VPD value.
-
Adjust: If your VPD isn't optimal for the current growth phase, adjust either the temperature or humidity using fans, heaters, or dehumidifiers. Ideally, the adjustment should be based on the leaf temperature measurement.
Optimal VPD values for cannabis cultivation
Choosing the right cannabis seeds from renowned breeders around the world is the first step to a successful harvest. High-quality genetics lay the foundation for vigorous growth and abundant flowers. Discover, for example, the exciting new Mixed Seeds collection at https://misch-shop.de/collections/misch-seeds and find varieties known for their vigor and yield potential.
Once you've laid the foundation with excellent seeds, optimize your growing conditions using the following general VPD guidelines (note that these may vary depending on the strain and specific conditions):
- Germination and seedling phase: Target VPD: 0.4 - 0.8 kPa
- Vegetative phase: Target VPD: 0.8 - 1.2 kPa
- Flowering phase: Target VPD: 1.2 - 1.6 kPa
- Late flowering phase: Target VPD: 1.4 - 1.8 kPa
Important note: Using leaf temperature instead of pure air temperature in VPD calculators provides more accurate values and allows for finer control of growing conditions.
Conclusion
The VPD chart is an invaluable tool for any ambitious cannabis grower. Combined with high-quality cannabis seeds, such as those found in the new Misch Seeds collection, and precise leaf temperature measurements with a laser thermometer (in conjunction with a VPD calculator, such as the one on Misch-Shop.de VPD calculator ), allows detailed control of growing conditions for optimal growth. By keeping an eye on the VPD and responding to your plants' needs, you can maximize your yields, improve plant health, and effectively prevent problems like mold.
