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Controlling Humidity in Your Home's Cannabis Grow Space


Humidity levels vary depending on the stage of growth for cannabis plants. For example, clones need to be between 70 to 80-percent humidity to grow properly. The last bit of the flowering stage is when your cannabis plants require the least amount of humidity to develop and grow big buds. This simple guide will help you maintain proper humidity levels throughout all stages of growth.

Humidity Levels Per Stage of Growth:

  • Clones – 70 to 80%
  • Vegetative – 40 to 70%
  • Flowering Stage – 40 to 50%
  • Few Weeks Before Harvest – Less than 40%

Cannabis growers use relative humidity (RH) measurements to create the ideal environment. Relative humidity measures how much moisture (water) is in the air in the grow space, compared with the max amount of water the air can actually hold at the temperature preferred.

The Effects of Humidity on Cannabis Plants

When the humidity level is too high for your cannabis plant’s position in growth, it will compensate by pulling moisture from the air or roots. When humidity levels are too high, the leaves take in moisture from the air. Low humidity results in the plant robbing water from the roots.

When RH levels are too high during the vegetative stage of growth, wet spots often form on the leaves of cannabis plants. Nutrient deficiencies and growth reduction is noticed if the RH reaches levels of 25-percent or less.

The flowering stage is where you really need to pay attention to RH and humidity in general. This is the most likely stage to encounter a mold issue in. Mold can form inside or on the buds. Internal mold formation isn’t always noticed before or even during harvest. Bud rot is another potential issue that can ruin your whole plant’s crop if it isn’t caught quick enough. The best way to prevent mold is to keep the air moving in your grow and make sure your humidity levels are carefully monitored – not to exceed 50%.

As you lower the humidity in the space to prepare your cannabis plants for harvest, you have the most potential to promote an increase in resin production. This will add potency to your buds. It’ll also make them look more crystallized with trichomes.

Harvest Time Humidity

The first stages of curing (drying buds) is crucial. You can still develop a mold issue even after the buds are clipped for drying. The humidity level should be between 45 and 55-percent, with 55-percent being dead on for ideal curing conditions. It may take a few extra days for your buds to dry completely, but this is the safest way to do it to prevent mold and ensure your buds don’t lose any important compounds.

Closing Thoughts

When growing cannabis, it is ideal to have a hygrometer in the space. The hygrometer will tell you exactly what the humidity is in the space. If you have a large grow, it’s ideal to have a hygrometer in every section of the space because humidity can vary slightly in different locations of the grow. Ensure that your humidity levels are appropriate throughout the entire growing process to produce bigger, more potent and tastier cannabis.

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