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What does humidity do for weed?

Consistency is critical, and with so many variables impacting cannabis growth, it is crucial cultivators have the systems in place to control these. One of the most important is the ability to manage humidity, protecting the plants from unwanted diseases and resulting in the most valuable, high-quality output.

Cannabis and humidity: a delicate balance

Like any other living organism, cannabis is affected by the climate around it. And, like other plants, when it absorbs the water it needs to survive and grow, it will consistently transpire this as water vapour through its leaves.

This presents an issue as, if there is no system in place to extract that moisture from the air, the cannabis plant will continue to absorb this moisture, as well as any water it is receiving from the soil. Too much water can be as damaging as too little is for these crops, as we will discuss in further detail later in the article.

For plants like cannabis, this prevents humidity levels from becoming too high or too low, consequently keeping it in the conditions required for the fastest and best-quality output.

In addition, there is not one static humidity or temperature that cannabis needs to remain at for its entire growth. For the best produce, the plant requires different levels of relative humidity (RH) across its lifetime, which we have outlined below.

Typical temperature and humidity for cannabis growing stages

24 – 27°C, 65 – 70% - Vegetation

24 – 27°C, 40 – 70% - Flowering

24 – 27°C, 40 – 50% - Late flowering

21 – 27°C, 30 – 50% - Drying

21°C, 50% - Curing

The consequence of uncontrolled humidity on cannabis growing

The fluctuating needs of the cannabis plant in terms of humidity place a huge priority on a well-managed environment that continues to meet its ideal moisture levels throughout its growth.

That is why grow rooms, greenhouses, and other indoor plant-growing facilities are used – to create a completely climate-controlled environment, helping to maximise plant production without the worry of external weather conditions changing.

But, if there is no dehumidification system in place to manage these conditions, it can lead to a number of nasty outcomes for your plants that affect their health, quality, and yield.

  • Bud rot (botrytis cinerea) Bud rot is considered one of the primary “crop-killers” of cannabis. This is a mold that develops in the dense cores of cannabis buds. Infections begin on the bud stem and from there spread further outwards. As a result, it is not easy to see bud rot with the naked eye early on. But once it has taken root, it destroys the surrounding bud, turning white, grey, and finally black, as well as slimy and mushy. By then, it cannot be used anymore. Most cultivators will cut out these infected areas and leave the remainder to grow. But, bud rot can lead to the plant spreading spores that go on to infect the rest of the crop, so it is often safer to remove any infected plants entirely. In either circumstance, if left unresolved, bud rot can lead to excessive yield reductions and profit losses for your cannabis growing.

  • White powdery mildew Another potential problem is white powdery mildew, a fungal infection that develops in high-humidity environments. This can develop from standing water in proximity to a cannabis plant, and again damage the overall health of it and the buds it is sprouting. While the early stages of cannabis development require a high humidity environment, the presence of proper airflow from your dehumidification system will help prevent this growing and wreaking havoc on your harvest.

  • Nutrient deficiencies When the air is too dry, plants will be compelled to drink through their roots to sustain themselves, especially in high temperatures. While this is great in moderation because of the nutrient-rich soil, overindulging in these nutrients can have negative implications. This can cause the plants to develop yellow or burnt tips as a result of nutrient burn. Subsequently, the plants lose leaf mass and robustness, restricting their ability to absorb ‘food’ in the form of light into their system. Cannabis plants are particularly vulnerable to this during their flowering stage.

  • Restricted growth Finally, above all else, if the humidity levels are not adjusted over time to best reflect the needs of the cannabis plant in its various phases, then it means the plant will not develop as fast or as healthily as it could be, reducing the quality of your output.

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