January 30, 2018 - Comments Off on All About Vapor Pressure Deficit (VPD) with Plant Health Specialist Kevin Jakiela

All About Vapor Pressure Deficit (VPD) with Plant Health Specialist Kevin Jakiela


We chatted with Modular Farms’ Plant Health Specialist, Kevin Jakiela to get the 411 on VPD and why it’s important for farmers to know what’s up. Vapor Pressure Deficit, also known as VPD, is a measurement of humidity determining the difference between the amount of moisture in the air and the amount of moisture the air can hold.  It is commonly used amongst farmers to optimize plant health and growth as an accurate measure predicting plant transpiration and water loss compared to relative humidity. Here, Kevin shares his insights on the importance of VPD, how it’s used and the benefits behind utilizing VPD in farming.

Kevin Jakiela, Research Scientist & Plant Health Specialist of Modular Farms Co.

Kevin calculates VPD based on three primary variables:

  1. General relative humidity of the farm
  2. Air temperature of the farm
  3. Temperature of leaf within a specific plant

He measures the air temperature and humidity of the farm using internal sensors and measures the temperature of a leaf using an infrared thermometer. Once he gathers all the variables, he plugs it into a VPD formula that shoots out a kPa number (pressure value). This number is then used as a reference point to see how the plant is growing. As a general rule of thumb, a broad optimal VPD range for plant growth is anywhere from 0.45-1.25 kPa. When growing a vegetative mature crop like Kale, 0.8 – 0.95 kPa is ideal. Overall, the most optimal VPD is dependent on the plant type and what stage of growth it is in. For example, the VPD for a seedling is very different compared to that of a 10 week old plant.

Farmers can adjust the farm’s interior climate through controls to create the most ideal VPD level for plants. The two easiest variables to change are air temperature and humidity. To put it simply, low VPD means high humidity, while high VPD means low humidity. Based on calculations, farmers will then adjust the farm accordingly to produce the best possible environment for its plants. For example, fans can be used in farms to increase air circulation – and Modular Farms are designed with fans built in for this purpose.  Make sure to avoid the danger zone, which is anything less than 0.4 or greater than 1.6! Plants will not thrive under those conditions.

VPD’s benefits include better crop growth, knowledge and overall, healthier plants! The ability to change the environment to grow better, healthier and tastier food is the biggest attraction behind VPD to farmers.  VPD does not solely apply to one single plant stage. Farmers should focus on each stage equally and measure VPD throughout the year because plant health matters all the time!

There are really no risks involved with manipulating VPD by adjusting the farm’s interior. The only way it can be risky comes down to human error. As long as calculations are correct, plants will always in turn become better!

If you would like to learn more details on VPD, Kevin recommends to read “How Vapor Pressure Deficit Helps Indoor Farmers” by Austin Yeany in Maximum Yield.

Published by: Jesse Brito in Farm Resources

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