Water Use and Transpiration Rates For Indoor Cannabis

Water Use and Transpiration Rates For Indoor Cannabis

If you’re new to growing cannabis indoors, you likely have lots of questions. Many inexperienced growers are surprised at the amount of water their indoor marijuana plants require in order to thrive. Conversely, the moisture in the air surrounding an indoor cannabis crop also needs to be removed to safeguard the plants’ health. Here, we’ll explore how to calculate indoor cannabis water use and transpiration rates along with other growing advice so you can grow a healthy crop of plants. 

Water Use and Transpiration Management: A Crucial Concern

Cannabis plants require substantial amounts of water to grow healthy. All this water ultimately evaporates or cycles into the air via the plants’ transpiration. That transpiration must be thoroughly managed or infections like powdery mildew are likely to occur. Controlling humidity within an indoor growing environment can be tricky, but it’s an essential step if you want to maintain the health of your crop. If you’re launching an indoor growing facility to cultivate cannabis, you must take water use and transpiration rates quite seriously, or you risk losing your investment.

Understanding Cannabis Water Use

Unfortunately, experts can’t tell you to water your cannabis once a day and leave it at that. There are many variables that affect the amount of water you’ll need to deliver on a routine basis. There variables include how densely your cannabis crop is planted, the room’s humidity, the room’s temperature, plant size, growing medium, and light intensity. All these factors, together, will impact how much water you irrigate your plants and how frequently you deliver that water. 

Once you arrive at a calculation for irrigation, you can scarcely get used to your routine before the crops’ water needs change. Even so, cannabis experts suggest beginning with 1,000 liters of water per day for a growing environment associated with 1,000 square feet. Your crop may not need this much water, but it’s better to have enough just in case. Remember that growing conditions within your environment will change; that means you’ll need to be prepared to change your irrigation routine as needed.

What Is Transpiration?

The water movement with your cannabis plant is affected by the evaporation of water at the leaves’ surface. Scientists refer to that water loss as transpiration. Another way to view transpiration is this: it’s the process where water and important nutrients move from through your cannabis plants from cell to cell. Transpiration also affects how the plants can obtain the carbon dioxide they need from the air and regulate their temperature. Multiple factors affect the rate of transpiration; these factors include the environment’s relative humidity (RH), vapor pressure deficit (VPD), and the temperature that exists at plant level and within the plant canopy. To keep tabs on these variables, growers rely on sensors to alert them to changes in conditions that could affect the health of the crop. 

When growing cannabis, expect that the plants will transpire roughly 95% of the water you deliver. It’s not uncommon for 99% transpiration to occur. While master growers tend to have the experience needed to monitor the health of their crops in association with transpiration, newcomers to the field may need to rely more heavily on alert systems. Some alert sensors are linked to HVAC systems that can automatically adjust to achieve improved temperature control for the environment. 

Maintaining Good Growing Conditions

Using proper equipment like thermometers helps you to keep tabs on your cannabis crops’ environment. Some novice cannabis growers make the mistake of ignoring the transpiration rate only to find out later that it’s much easier to maintain a healthy environment than to contend with fungal infections like powdery mildew. Too much humidity can also lead to the tip burn and wilting. Understanding VPN rates and transpiration allows you to manage your HVAC system more effectively too, which is a key element for producing a healthy crop yield. 

When growing your cannabis, aim for a VPD range of .8 to 1.1 while the crop is still in its vegetative growth stage. Aim for a VPD range of 1 to 1.5 when the plants reach their flowering stage. As complex as some of this information may seem, growers can calculate VPD fairly simply. In order to make an accurate calculation, you’ll need to know the room temperature and its relative humidity. Then, you can apply this formula:

(100-RH/100) x SVP (saturated vapor pressure) = VPD

Use your calculation to ensure that your crop is growing within the acceptable range. If not, adjust your HVAC system, making changes until you achieve the optimum range. You can also find convenient VPD calculators online. Simply plug in your numbers and the calculator will give you your VPD.

Using Equipment to Control the Environment

Indoor cannabis growers must rely on some advanced HVAC solutions in order to grow a healthy crop. Your HVAC system allows you to support the optimum growing conditions for your plants. A top-functioning dehumidifier is a crucial part of your HVAC needs as it removes the excess humidity from the air–the humidity that can cause unwanted fungal infections for your plants. 

Air extractor fans are another important element of your indoor growing apparatus. These fans help you to remove hot air from your room and introduce fresh air into the space. Your cannabis plants will also require grow lights to ensure their light requirements are met. 

Use an Integrated Environment Control System

While it may require some investment on the part of the grower, an integrated environment control system will help you control the variables that affect growing conditions in your environment. These systems allow growers to maintain tighter control over their space’s temperature, dewpoint, and more. The right equipment means that you don’t have to worry about your crop day and night. 

Other Challenges for Calculations

Keep in mind that growing cannabis on a commercial level is still in its infancy. As small-scale growers move to expand their growing space and increase their crop yield, recommendations are apt to change. Equipment like portable dehumidifiers and standard types of air conditioners may not provide the ideal support that more expansive environments need to produce a healthy cannabis crop. When choosing equipment, you’ll want to make sure it can meet your environmental control needs; on the other hand, installing an HVAC system that’s too large could lead to unnecessarily inflated energy bills. 

Beware of Colder Temperatures

Controlling heat and humidity is important to reduce the risk of mold and mildew infections, but don’t run the risk of opting for cooler temperatures than is recommended either. Cooler temperatures will result in slower growth of your cannabis plants. When the plants’ growth is reduced, the rate of photosynthesis is also reduced. In cooler tempers (those below 65 degrees Fahrenheit, the plants’ root systems struggle to hold dissolved oxygen, which results in a struggling plant. That plant will be more vulnerable to pathogens like mold, particularly when conditions are both cool and damp. 

The fact is, in many ways, indoor cannabis is more vulnerable to colder temperatures than outdoor cannabis because of the more humid environment. Of course, you want to avoid letting temperatures exceed 80 degrees F too. When it’s too hot, the plants will also stop growing. Maintaining healthy ranges for your variables like temperature and VPN mean the difference between a healthy and unhealthy crop of marijuana plants. 

Creating an Environment that Supports Healthful Transpiration

Optimum watering and attention to the environment allow growers to support healthful plant transpiration. Using the right equipment enables you to ‘manipulate’ your space to achieve optimum growing conditions for cannabis. While we’ve discussed humidity and temperature, we haven’t covered air circulation yet. That’s an important factor that some growers might overlook. 

Good air circulation helps you to strengthen plant shoots. By improving air circulation with oscillating fans, for instance, you actually cause the plants to sway. That swaying motion, gentle as it is, can cause micro tears to occur in the plants. As the plants heal, they actually become stronger as a result. Good air circulation also enhances humidity control. Without it, again, your cannabis may be more susceptible to mold and powdery mildew conditions. 

Take care when designing your growing space and environment. Growing cannabis requires investment. You can protect that investment and your crops by adhering to best practices regarding things like transpiration rates and water use calculations. Use the tips outlined here to help you achieve the ideal conditions for your plants. Remember to calculate VPD often and, if possible, invest in a good integrated environmental control system. You should find that your diligence and investment are rewarded with a healthy crop of plants. 

Remember that FloraFlex can provide you with the products and solutions you need to grow your cannabis crop. No matter the scope of your project, we can provide you with everything you need to make it a success.