how to prevent MOLD on your indoor (or greenhouse) cannabis plants
Below are the 6 things I DON'T do, to keep my indoor garden mold-free!
Various fungi, especially molds, are a common problem for many cannabis gardeners - indoor and out. Some affect the plant during the vegetative cycle, as root, stem, and leaf growth is building up the plant's size. Others target the flower buds, dense moist zones often ripe for fungal colonization. Some fungi (like the common powdery mildew) can affect cannabis at pretty much any stage.
Without getting deeply into the science of fungi (you can do that here), they absorb water and decaying plant matter, to form proteins to build their structures (to grow, reproduce, etc):
I don't recommend using any fungicides on your plants. If you have really moldy (or dead) leaves it's best to cut them off and discard them. If possible, get rid of any plant that shows any mold at all (although this loss can be hard for many indoor gardeners to bear).
To prevent mold from ever appearing on your plants in the first place...
- humidify or mist
- spray foliar treatments
- allow stagnant air
DO NOT overwater
The more often your soil is wet, the more often the air around your plants is extra damp, leading to opportunities for mold. Most cannabis growers overwater - even professionals with decades of experience! Generally, don't water your plant until it begins to look thirsty. Get good at spotting that before you water. The plant shouldn't look wilted, that's too thirsty! Another clue is the soil itself. If there's any moisture near the surface of the soil, you shouldn't water.
When you DO water, water slowly so that it can soak into the soil evenly without any spilling out the bottom. Only water until the majority of the soil is damp, ideally not running off any nutrients via overflow. It depends on conditions and strain of course, but many indoor plants don't need watering more than once every 8 days or longer!
DO NOT overheat
Many growers believe cannabis plants prefer hot, humid, jungly conditions. While some strains can grow like that, many prefer more moderate temperatures. Room temperature in most houses is fine. Some basement gardens may need to consider temperature, although generally speaking the light source is enough heat.
In many larger indoor gardens, large fan systems are needed to keep temperatures down. When the fans break down, mold becomes a huge potential threat to the crop. Heat helps breed mold. Without shocking your plants of course, always keep your temperatures down!
DO NOT humidify or mist
Again, cannabis plants don't usually prefer a jungle. Many indoor gardeners swear by humidifying the air, but I've more often just seem this leading to mold. Even young plants don't need to be misted, as so many people think they do! As long as the air isn't bone dry, and you're watering the soil properly, the stems and leaves don't need watering directly.
DO NOT spray foliar treatments
Foliar sprays for various reasons (extra nutrients, insecticides, fungicides, etc) all add moisture to the parts of the plant that don't need it, encouraging mold growth.
Many chemicals, while having a beneficial effect, also interact with the plant's internal chemistry, such as its immune system, leading to unintended consequences. Remember to never use neem on cannabis for any reason.
DO NOT fertilize
Cannabis plants require nothing - nothing at all - except light, air, water, and soil. Soil-less gardens obviously must add nutrients another way, generally as liquid products added to the water supply. But plants in soil have everything they need to grow large, produce cannabinoids, and return seeds if desired.
Fertilizing cannabis plants is done to increase yield at the expense of quality, and a decision every gardener makes for themselves. I'd rather get a little less weight, and have it all be clean and delicious.
If you fertilize, remember that this is often a cause of pH problems, and plants with pH problems are prone to mold.
Also remember that fertilizing can burn leaf tips, and dead leaves are a source of nutrients for mold.
DO NOT allow stagnant air
Use a fan (and vents in greenhouses) to keep air flowing around and through your plants. This helps with gas exchange (necessary for photosynthesis), and helps dry any moisture lingering on the plant surface. As buds get heavier, airflow is increasingly important if there's any dampness.
Trim excess vegetation. Lower leaves can be removed completely as the plant matures. Dense areas can be thinned.
Don't place your plants too close to walls or each other. Space is precious for indoor gardens, but crowding encourages mold!
May all your leaves be mold-free and all your buds frosty!
Thanks for reading. Hopefully you learned something new, or thought about something in a different way. Please comment with your own mold-prevention tech & tips, and share this info with anyone it could help!