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Vapour Pressure Deficit in Marijuana Plants: What you need to Learn

vapour pressure deficit in marijuana plants

Growing Marijuana is both a sort of adventure and education. Just like other kinds of plants, Marijuana growing will need enough knowledge and idea so that it will turn out into the best kind of cultivation. As growers, there are many things and concepts you have to understand so that you will become an effective grower.

To ensure that your weeds will produce potent buds, you need to make sure that you are giving everything your marijuana plant needs.  Because of the several needs of Cannabis plants, growers sometimes forgot the importance of those so called “little needs”. Many growers fail to realize that all the needs of weeds are essential and it should be equally and properly given to them because all these needs are important in the whole growth of Marijuana plants.

One of the greatest yet overlooked needs of weeds is the humidity. Whether you like it or not, humidity plays a vital role in growing Cannabis plants.  Humidity is a way for you to determine how flexible your plant is when it comes to mildew or how much your plants need in order to drink.

This topic is all about Vapor Pressure Deficit and what its role in Cannabis growing is. It talks about the factors affecting VPD and what are the things every grower should know when it comes to VPD.

What is VPD?

Vapor Pressure Deficit or VPD is the difference between two things, the moisture amount in the air and amount of moisture air can hold when it is saturated. There are two things that have a big part in VPD. These are the temperature and humidity.

These two things have a strong relationship with each other. Temperature talks about the degree of heat in a certain substance, while humidity is the state of being humid or having high level of water vapor in the air. When it comes to Cannabis growing, temperature has an important role to play while humidity has a great effect to the plants.

Humidity matters a lot

Humidity is an important factor in growing weeds. This is because your plants will need a regular water intake. However, you must bear in mind that when there is higher humidity in your grow room your weeds will be using its leaves to absorb the water in the air letting the plant to decrease their water consumption in the roots.  On the other side, if your grow room has low humidity, the leaves of your pot will pull water from the roots.

With right humidity, you could able to help your plants grow healthy and vigorously. Since the water has nutrients to feed on your weeds, it is important to know how much water your plants need depending on the humidity of your room. In that way, you could able to control the nutrient intake of your weeds, and letting the leaves of your pot to grow healthy. With right humidity, you can have a great control of normal growth of your weeds.

Relative Humidity (RH) in your plants

Measuring the relative humidity can be easily done through using an instrument called hygrometers. Relative Humidity talks about the ratio of water vapor’s partial ratio to the equal water vapor pressure at a given temperature.  Relative Humidity has a big effect in the whole growth of plants. For some growers, they prefer to make the humidity of their grow room in range, however for some growers, giving a right RH to their plants means a lot.

RH has a direct effect on the plants. Just like human being, plants will also need transpiration (to release water vapor using their stomata) in order to breath because this is part of their growth. With that, the amount of water used by plants in the process of transpiration will be regulated. This is how relative humidity directly affects the plants.


On the other hand, the temperature should always be at the right point to ensure a good health for your Marijuana plants. Your plant’s temperature should not be too cool or too hot or else it will give negative effect to your plants. Having a right temperature for your grow room will help your weeds grow healthy.

Vapor Pressure Deficit in growing weeds 

Talking about VPD is knowing what your weeds really feel and how it will react to the overall humidity in its growing environment. Second way to think VPD is thinking the demand of atmosphere for water. Measuring VPD in units is in milibars and kilopascals; this is a combination of temperature and RH in a single value. Always remember that how VPD run is opposite to RH. This basically means that when the RH is high then the VPD is low. When VPD is high, there is higher possibility that the air is sucking the moisture in the plant.


To fully understand the impact of VPD in growing weeds, VPD will give the exact picture of what the plants feel in their environment considering the temperature and the humidity. This gives the growers a chance to give better ways and platforms for environmental control. However, you should be aware the VPD is difficult to determine exactly. Your choice will be to measure the temperature of the air in your growing room.

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