"VPD tells you how a plant is feeling"

VPD is an important value because it can tell you how a plant is feeling. VPD stands for Vapour Pressure Difference. The company 30MHz expresses this in VPDleaf. This visualization shows the data from their wireless sensors, which provides better insight into the health of your crop.

What is VPDleaf?
"VPDleaf is extremely reliable because the measurements are taken at the micro level, all the way down to plant level," the 30MHz team explains. "Using these measurements and improved formula, a grower will have the most accurate data possible at his disposal. The improved formula – which leads to VPDleaf – is endorsed by WUR (Wageningen University & Research)."

Why is VPD important in horticulture?
If the VPD is zero, plants can not transpire effectively. So the VPD is an important factor in creating an optimal growing environment. It can influence various key elements, which are connected to each other. As VPD increases:

• The uptake of CO2 decreases.
• The increasing difference in vapor pressures between the leaf and the air causes the crop to evaporate.
• VPD increase → transpiration increase → thirst! The plant needs to draw more water from its roots.
• All this combined, leads to more stress. And that could lead to a weaker plant.

So VPD affects the plant's loss of water (transpiration). Sometimes the air in a greenhouse gets too dry during the day. This can cause a plant to 'turn off'. When the air is too dry, photosynthesis will stop to prevent the plant from exhausting. Photosynthesis is the process used by plants to convert sunlight, water, and CO2 into oxygen and energy that is used for the growth. The crop will miss hours of daylight which leads to a decline in health. An optimum VPD can help in the prevention of mold and plant diseases.

Research in tomato production in 2017 showed that VPD regulation efficiently moderated plant water stress and maintained the plant's water balance. The researchers concluded that when you regulate the VPD, you'll be more efficient with irrigation.