How to Grow Cannabis in Humid Climates

The steepest challenge to growing cannabis in a wet environment is preventing mold. Mold like botrytis, or bud rot, cannot be cured once it has established, and will lead to at least the loss of the affected bloom, if not the whole plant. And it spreads quickly. The best defense, then, is to prevent it altogether by tracking and regulating humidity as best you can. Obviously this will be easier for indoor growers or those with a controlled environment, but there are steps outdoor growers can take as well to keep their plants healthy.

In this article, we review how to grow marijuana in wet climates, tips for preventing bud rot, and which strains are best suited for damp or humid environments.

Cannabis prefers relative humidity levels around 40-50%. While this varies depending on who you ask, most growers agree that anything below 40% is too dry, and anything over 60% is high risk for mold or other damage. When growing indoors, a hydrometer is always recommended to at least track the humidity levels.

Of course, when growing outdoors, tracking humidity may be an exercise in misery since there’s nothing you can do to change it, but in either case, steps can be taken to improve airflow and reduce moisture around your plants

Ventilation

Regardless of where you’re growing, you can prevent mold by improving ventilation. First and foremost this means having a proper ventilation system in your grow room.

Having proper airflow and ventilation is essential if you're growing cannabis in a humid climate. photo credit

A couple clip-on fans are not going to keep plants safe in the relentless humidity of Florida, for instance. If at all possible, install an inline fan with filters to keep their air around your plant moving and clean.

Pruning

Both indoor and outdoor growers can improve ventilation by strictly pruning the plants as they grow. Removing superfluous branches and fan leaves will help air flow around the plant, while additionally removing shaded areas. Mold prefers the dark, so shedding more light on the plant will minimize mold’s growing conditions while also bathing your buds in light. Win-win.

Dehumidifiers

Just as some growers in arid climates use humidifiers in their grow tents or greenhouses, dehumidifiers may be used in wetter climates to draw moisture from the air.

If you are growing outdoors in a rainy region, dehumidifiers are not an option, but it is recommended you step outside after a rain to shake your plants free of any excess water that may be pooling in deep crevices.

Soil and Plant Health

Most mold establishes early in the flowering phase, but preventing mold and other diseases is a holistic process that begins at the seedling stage, or even before. Soaking seeds in solutions like kelp extract can give seedlings a healthy start. Promote microbial life in the soil, including beneficial root fungi, by mixing in fresh compost or mulching.

Mulching is nearly necessary in hot dry climates to prevent evaporation, but in wet climates mulching can be used to improve surface drainage, preventing water from pooling on saturated soil. Standing water could attract pests or rot shallower roots.

Sanitation

Another free and easy way to prevent mold is to keep your grow room as clean as possible, even going so far as to change your clothes before stepping inside, especially if you have previously been outdoors. All manner of mold spores and pests can cling to your clothes and follow you inside.

Freshly harvested buds will need to be trimmed and dried in one order or another, and the decision depends on your local humidity. “Dry trimming” is generally recommended for dry climates, and involves drying whole branches or other large pieces intact so the buds can draw from the residual moisture before they are trimmed and cured. Dry trimmers trim dried bud.

Wet trimming is typically favored when growing in humid climates. photo credit

Wet trimmers, then, trim wet bud, completely separating the pieces from any other living (wet) plant matter before they dry. Wet trimming is recommended for wetter climates because the humidity in the air will prevent the buds from drying out too quickly. Any additional moisture those buds are allowed to draw from will keep them too wet, and result in a high risk of rotting before they can be cured.

The best chance you can give yourself for a successful harvest in a wet climate is to cultivate strains adapted to the damp.

Ancient sativas like Thai and Durban Poison once grew wild in tropical humidity. Their long stalks and thin canopies are naturally well-ventilated, and many of them have developed resistances to mold. Modern strains with sativa genetics include Bruce Banner, Super Lemon Haze (or any haze, really), and sativa-dominant hybrids like Head Cheese.

Northern Lights is not a sativa, but it is rumored to have originated in the Seattle area, and seems well-suited to the rain there. Similarly, Blackberry Kush carries indica genetics but has proven to be resistant to both cold and mold.

Growers in humid climates will need to negotiate humidity levels to prevent bud rot. Bud rot is the slang for botrytis, a fungus that forms on a variety of organic matter. On a cannabis plant, botrytis establishes in the deep crevices of the buds where it is nearly impossible to detect until it’s too late. Once you see bud rot on your plant, it’s likely already been there for several days. There’s also little to be done to keep the deep reaches of your flowers dry except for regulating humidity as best you can.

Prevent mold by keeping optimal ventilation around your plants. Both indoor and outdoor growers will benefit from carefully pruning their plants to increase airflow and light exposure, which also inhibits mold growth. Indoor growers may employ dehumidifiers to collect excess moisture from the air (but this water should not be used to feed the plants).

Use the tips in this article to grow happy, healthy plants! photo credit

Additional strategies to keep plants healthy in the humidity include soil health and sanitation. Compost, mulch, and other organic substrates add beneficial microbes to the soil which help combat molds. And holistic care beginning at the seedling stage, including organic solutions like liquid seaweed can improve plant’ immune systems.

But the best chance of a successful harvest begins with choosing a strain that is adapted to damp conditions. Sativas like Durban Poison, Bruce Banner, and Super Lemon Haze are all descended from tropical landrace strains. And even indica hybrids like Northern Lights and Blackberry can survive cold, wet conditions when well cared for.

How do you keep your plants healthy in a humid climate? Keep the conversation going in the comments below!