No matter how supreme your mother plant or how advanced your lighting system, a lack of proper humidity control in your indoor cannabis cultivation operation will limit the production of secondary metabolites, and therefore the potential of your business as a whole. Compromising on your humidity control capabilities can substantially reduce the quantity, quality and consistency of finished products that consumers and manufacturers demand in today’s market.
Robbie Batts, Inspire Transpiration Solutions
Humidity impacts almost every aspect of a grow operation - including photosynthesis and transpiration, VPD and nutrient uptake, pest and pathogen pressure, room temperature and leaf temperature, and ultimately the yield and quality of the product you are growing. Accurate and consistent humidity control will reap great rewards in the increasingly competitive arena of indoor horticulture.
Indoor vs. outdoor horticulture
Whether indoors or outdoors, transpiration is an important physiological process that plants go through to take in nutrients and maintain turgor pressure. Transpiration results in plants releasing water into the air, which has a significant environmental impact on both temperature and relative humidity. Many growers choose indoor cultivation for the year-round productivity and environmental consistency that outdoor cultivation doesn’t offer. When plants are outdoors, transpiration is affected by a number of different factors that are out of the control of the grower (wind, temperature, sunlight, etc.) Growing indoors allows cultivators to take control of crucial factors like temperature, relative humidity and airflow and ensure they are maximizing the output of their efforts.
While environmental control is a huge benefit to growing indoors, it doesn’t come without its own challenges and pitfalls. Mistakes in this process can lead to troubling and costly microclimates, moisture issues and pathogen proliferation. These issues can cause the health and vitality of your crop to suffer, ultimately leading to a decrease in product quality or complete crop loss, which means revenue loss for your business. Humidity is a critical component of controlled environment agriculture, and due to the nature of the spaces involved, is often the most energy intensive and difficult to control.
The right balance of air and water
Plants need several basic inputs in order to grow: light, water, nutrients, oxygen, root zone temperature, microbes, temperature, humidity, airflow and carbon dioxide. Plant systems are interconnected in such a way that growers must understand the impact of one input on potentially several others.
In cannabis cultivation, we use relative humidity to describe the amount of water vapor in the air, expressed as a ratio of actual vapor pressure to the saturated vapor pressure. It is important to talk about relative humidity as opposed to absolute humidity to truly understand environmental control, because hot air holds more moisture than cool air. The right balance of air and moisture is critical for processes like transpiration, VPD, and CO2 uptake to occur, which promote optimal plant growth and secondary metabolite production.
Transpiration directly impacts VPD, or the pressure difference between the intracellular membrane of a plant’s leaf and the air of a grow room. VPD is the physical force drawing water vapor up the stem from the roots and out of the leaf. A VPD that is too low will inhibit transpiration, decreasing the rate at which water and nutrients flow through a plant, which ultimately will slow growth.
Relative humidity and the plant life cycle
Genotype + Environment = Phenotype. Some plants grow better in different relative humidity ranges during different stages of growth, so growers must control relative humidity specific to each stage of the plant life cycle. Doing so can influence plant vitality, product quality, genetics, and overall yield. Indoor grow rooms are most likely to struggle with high relative humidity levels, which slows down the transpiration process and can have many negative impacts on plant health and secondary metabolite production.
In all stages of growth, cannabis plants need a constant intake of water, but the amount of water they need will fluctuate based on a variety of factors. Because humidity will directly impact how much water your plants take in, controlling the humidity gives growers increased control over nutrient uptake and therefore control over plant growth and plant health.
Humidity also has a direct effect on disease and pest infestation issues such as powdery mildew and botrytis. Mold and fungus can quickly lead to crop loss and revenue loss, especially as legal markets continue to conduct microbial testing that looks specifically for molds, mildews and pesticides.
How do we effectively control humidity?
Effective and efficient humidity control begins with right sizing environmental control systems like heating, ventilation, air conditioning and dehumidification (HVACD) specific to your unique operation. HVACD equipment can be used to maintain temperature, manage humidity levels and minimize threat of disease at each stage of the plant growth cycle.
Source: Fluence by OSRAM
Right-sizing cultivation and curing HVACD systems means balancing capital costs with risk tolerance to maximize profit and optimize long-term operating expenses, all while ensuring the system has the capacity required to manage your environment and meet your production goals.
Even small changes in humidity setpoints can have a dramatic impact on both plant growth and equipment selection. Humidity is one of the most critical factors in cannabis cultivation, yet many growers lack a complete understanding of controlling and manipulating humidity levels to maximize plant health and yield, minimize risk of disease, and increase revenue.