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The Effect of Vapor Pressure Deficit on Plants Growth

The Effect of Vapor Pressure Deficit on Plants Growth

As a grower, we’re always on the lookout for the best growing techniques, tips, and tricks to maximize our yields. If you still haven't explored how vapor pressure deficit can be beneficial, then you are missing out on one of the best tactics for monster yields! Just ensuring the best genetics and nutrients is not enough, optimizing the humidity and temperature will help your plants reach theirm maximum potential.

The best growers have figured out how to manipulate VPD to keep the stomata on their plants open, which results in the plants taking up as many nutrients as they can, resulting in explosive growth. Today, we will discuss how you can do this on your own, but let's cover some basic information on vapor pressure deficit first.

WHAT IS VPD?

While 'Vapor Pressure Deficit' (VPD) sounds like a complicated term, it is no rocket science. Expert growers simply use the term to refer to the combined pressure of leaf temperature, relative humidity, and air temperature. In simpler words, vapor pressure deficit describes how a plant feels and reacts in its current environment – including the temperature, pressure, and moisture content. One other way to look at this is that VPD is the vapor pressure deficit between the leaf's conditions and the air’s condition. If you have a dry and hot grow room, your plants will transpire rapidly, seeking to balance out the leaves' conditions and the grow room. On the other hand, if you have a relatively humid environment, the plant will not transpire as much since the conditions in the grow room are closer to the plant's conditions, i.e., they are moist.

WHY IS VAPOR PRESSURE DEFICIT IMPORTANT FOR PLANTS?

If the vapor pressure deficit is really high, the plants will transpire heavily. This means that they will be absorbing and storing more nutrients – which can even lead to overabsorption, causing toxicity. On the other hand, a low vapor pressure deficit can also cause problems. Plants won't transpire, meaning they will not absorb fresh nutrients and can develop deficiencies. You can easily manipulate VPD as a grower and encourage plants to let their stomata stay open to expel moisture into the growing environment. As a result, there will be maximum nutrient uptake through roots. To accommodate for the lost moisture, the plants require more moisture through their roots. Later, when you feed your plants nutrients through the root zone, they get absorbed along with the moisture (which is just how feeding works). However, if you can dial in the optimal vapor pressure deficit range, it'll end up in a healthier plant.

HOW CAN YOU CALCULATE VPD?

Honestly, by far, the easiest method to calculate vapor pressure deficit in the grow room is by following a VPD chart. Here's one VPD chart below:

AIR TEMPERATURE 77 degrees Fahrenheit (25 Celsius)
LEAF TEMPERATURE 73.5 degrees Fahrenheit (23 Celsius)
RELATIVE HUMIDITY 50%

DOES VPD AFFECT THE PLANTS' CO2 UPTAKE?

Most growers wonder how vapor pressure deficit affects a plant's CO2 uptake. When you attempt to push the plant to its highest growth potential, it becomes capable of taking up CO2 more readily. It means that if you're focusing on dialing your vapor pressure deficit in, you can absolutely benefit from CO2 supplement.

WHAT WILL YOU NEED?

Hygrometer

To begin to measure the vapor pressure deficit, you can use an infrared thermometer to measure the leaf temperature (ideal, but not necessarily required). Also, use a hygrometer and keep the probe by the canopy. Once you know the leaf/canopy, air temperature, and relative humidity, you can calculate the VPD. To start, you will need the temperature in Celsius. [(Fahrenheit – 32) *5] = Celsius Example: [(77F – 32) * 5] +25 So, 77 degrees Fahrenheit would be 25 degrees Celsius. Begin by calculating VPsat (pressure within the leaf).

CALCULATE VPD USING A VPD CHART

Not everybody has time to calculate conditions in their rooms continually, and fortunately, you do not have to. As an alternative, you can simply follow a vapor pressure chart. It shows all the possible vapor pressure deficit readings across various temperature and relative humidity levels. When you have the VPD chart in front of you, you can calculate the ideal range for your plants' growth and adjust humidity and temperature as needed to sustain the perfect level throughout each phase of growth.

MANIPULATING VAPOR PRESSURE DEFICIT

If you calculate your Vapor Pressure Deficit and find it to be too high or too low, you can make adjustments to fix it. All of this comes down to adjusting the relative humidity, temperature, or both. It can be done with multiple types of equipment, based on exactly how you need to adjust the environment. These include:
Humidifiers
Dehumidifiers
Heaters
Air Conditioners

You can manipulate your Vapor Pressure Deficit with a simple ventilation system. You can even fine-tune how often you expel air while bringing fresh air inside by setting up exhaust and intake cycles.

THE BOTTOM LINE ON GROW ROOM VPD

Now that you have already understood the importance of VPD and learned how to use it, you are good to go in perfecting your growing room environment. In the end, it all just comes down to finding the VPD chart and balancing up your humidity and temperature to be in the green zone. It does sometimes get complicated but does not necessarily have to be.

May 12th 2021