Cannabis Bud Rot Prevention Guide
Learn how to prevent cannabis bud rot and keep your THC products fresh and potent.
Quick answer
Bud rot is a Botrytis infection that rots cannabis flowers from the inside out. Indoors, you avoid it by holding flower-stage humidity at 40 to 50 percent, moving air through and under the canopy, spacing plants so leaves never touch, and keeping buds dry at all times. It spreads fastest when the room swings from warm and humid to cool, or when airflow stops for even a few hours.
Cannabis Bud Rot Prevention Guide
Prerequisites
- A hygrometer and thermometer placed at canopy height
- An exhaust fan sized to the room, plus a dehumidifier on a controller
- One or two oscillating fans that stir air without pointing at colas
- Pruning shears, alcohol wipes, and a sealable trash bag
- A small flashlight for bud inspections
Step-by-step prevention
- Set the flower-room humidity target at 40 to 50 percent and run the dehumidifier from the first day of 12/12.
- Keep lights-on temperature near 75 to 80 F and hold lights-off temperature within 5 to 8 degrees of it.
- Mount the exhaust fan to pull air out at the top of the tent or room, where heat and moisture collect.
- Place oscillating fans so they move air across the canopy and along the floor, not straight into buds.
- Space plants so every cola gets light and air, then remove lower growth that sits in still air.
- Defoliate in stages during weeks 1 through 3 of flower, taking large fan leaves that block airflow between colas.
- Water at the base of the stem, never over the top of the plant.
- Empty runoff trays and saucers within an hour so standing water does not raise room humidity.
- Clear dead leaves, dropped petals, and spilled soil from the floor and pots.
- Wipe shears, gloves, and trellis clips with alcohol between plants.
- Run the dehumidifier on a humidity controller, not a timer, so night humidity stays level.
- Cut heavy nitrogen feeding late in flower, since soft leafy growth holds moisture against buds.
Airflow targets
- Canopy airspeed: gentle leaf movement, no fluttering colas
- Air exchange: exhaust clears the room every 1 to 2 minutes
- VPD in flower: 1.2 to 1.5 kPa
Bud checks
Look at colas every day from week 4 of flower. Aim a flashlight at an angle across the bud. Early bud rot shows as a single sugar leaf turning brown or gray, a dull brown patch with a soft center, or gray fuzz where the bud meets the stem. A bud that feels dry on the surface but soft inside is suspect. Do not squeeze buds to test them, because your fingers move spores to healthy plants.
How to Stop Bud Rot From Spreading in Cannabis
If you find rot
- Shut off the fans before you touch the plant so spores do not travel.
- Cut the infected cola 1 to 2 inches below the rot with clean shears.
- Bag the material, seal the bag, and carry it out of the building.
- Wipe the shears and your gloves with alcohol.
- Inspect the plant and its neighbors, then drop room humidity by 5 percent.
- Harvest early if rot shows on more than a few colas, because a slightly early harvest beats a lost crop.
Prevention beats treatment
No spray fixes bud rot on a flowering plant, and any product applied to buds leaves residue you will smoke. The work happens before the rot appears: low humidity, steady temperature, strong air exchange, open canopy, and dry buds. Hold those four conditions and Botrytis has no window to start.