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Medical Marijuana and VPD

vapor pressure deficit chart

So What is VPD?

VPD stands for Vapor Pressure Deficit. This is extremely important when it comes to monitoring your plant's growth. VPD helps growers maintain a consistent process for their plants. VPD is affected by almost everything in your grow; the lights, your plant temperature, air temperature, nutrient uptake, and other plant processes. This chart helps growers determine a few handy absolutes that keep your grow consistent and optimized. 

How to Decypher The Chart

The main components of determining your grow rooms Vapor Pressure Deficit are temperature and relative humidity. Temperature on the  Y-axis and Relative Humidity on the X-axis. When you have lower temperatures and higher humidities there is a good chance that your grow room is too humid. On the other hand, if you have higher temperatures with lower humidity levels then your grow room isn't humid enough. Your plants will transpire too quickly and run dry. When your humidity levels are just right in combination with the appropriate temperature, your plants will yield as much as they possibly can. Your plants will transpire at a natural rate, and thus be able to retain moisture in their leaves which will help your plant grow much stronger and yield more. 

You'll want to aim for the dark purple values to optimize plant growth. The light purple values are values that are acceptable and considered well balanced for a typical grow but you still might lose out on a small percentage of yields if you miss that sweet spot in the middle. If you operate most of your grow in the light green section of the chart, then you'll likely have plants that are drooping because they are too moist and unable to transpire properly. The leaves will be dark and heavy due to the retained moisture in the plants. If you operate in the darker green section of the chart, your plants will likely dry out and yield less. These leaves will be brittle and light due to transpiring too quickly. 

Is VPD Really That Important?

One mistake most growers will make at one point or another is watering a plant when it doesn't need it. If you don't know your VPD, and your plants look dry you would naturally assume they need water. Unfortunately, the plants need a more humid environment and watering them will only inflict further damage on your plants. You'll significantly increase your risk of root rot and your plants will start to show signs of nutrient burn. VPD helps growers understand the underlying needs of your cannabis plants and helps provide a consistent environment for your plants to grow over and over again.

Is There More I Should Learn?

Absolutely, we always recommend understanding and learning as much as you can regardless of your experience level. Growing your own medical marijuana is challenging and takes a lot of time and effort. A little knowledge goes a long way. There are formulas for determining a precise VPD without a chart. There are even equations for the values that you enter into the VPD formula. There's a ton to learn, however, we don't want to confuse you. Learning to read and utilize the chart above is your first step and will ultimately lead to the same results. Learning as much as you can but don't get lost in the details when you are first starting out. Remember to keep proper ventilation throughout your grow and maintain temperature and humidity levels in accordance with this chart and you'll be happy with your results. 

If you're having trouble controlling temperature and humidity levels in your grow, simply add a dehumidifier and a humidifier to your grow space and adjust relative humidity levels with those two tools. When modifying temperature simply apply and intake and exhaust fan to your grow space to keep fresh air coming in and out of the tent. Keep an oscillated pole fan running and that should keep a proper airflow throughout the grow and help maintain appropriate temperature levels. 

Grow Your Own Medical Marijuana in Missouri 

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