How to Spot and Stop Humidity-Driven Bud Rot

Humidity: it’s a love-hate relationship for cannabis growers. Your plants need it—but too much of it can turn your prized buds into moldy mush. Welcome to the dreaded world of bud rot (a.k.a. Botrytis cinerea), a fast-moving fungal foe that thrives in high-humidity environments and can wipe out your harvest before you even realize it's there.

If you're growing weed at home, especially indoors or in climates with fluctuating moisture, this guide will help you spot the early signs and take action to stop bud rot in its tracks.

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What Is Bud Rot, Really?

Bud rot is a fungal infection that starts deep inside dense cannabis flowers. Once inside, it spreads from the core outward, devouring your bud from within. By the time you see it on the surface, it’s likely too late for that cola.

Scientific name: Botrytis cinerea
Thrives in: High humidity, poor air circulation, damp conditions
Targets: Dense buds, especially in late flowering

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How to Spot Bud Rot Early

Detecting bud rot before it spreads is key. Here’s what to watch for—inspect daily during late flower!

Visual Signs:

• Gray or brown fuzzy mold inside or on buds

• Darkening of pistils or a sudden color change

• Shriveled sugar leaves sticking out of buds

• Mushy or slimy bud centers when gently squeezed

• Leaves falling off buds with no resistance

Smell Check:

• A musty, mildew-like odor that doesn’t match your strain's normal terp profile

• A dull, rotten smell when you sniff colas up close

Bonus Tip:

If you’re unsure, slice open a suspect bud—if the core is gray, brown, or fuzzy, chop it immediately and isolate the area.

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What Causes Bud Rot?

Bud rot loves:

• Relative Humidity (RH) over 60% during late flowering

• Temps between 65–75°F

• Poor airflow in or around buds

• Overwatering or trapped moisture

• Wet conditions after rain (for outdoor grows)

Basically, it’s the botanical version of a dank basement.

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How to Stop Bud Rot from Spreading

1. Remove Infected Buds Immediately

• Use sanitized scissors

• Cut at least 2–3 inches below the rot zone

• Do NOT compost infected buds—trash them far from your grow

• Disinfect scissors between cuts

2. Increase Airflow

• Add oscillating fans

• Open vents in grow tents

• Slightly increase exhaust speed

• Don’t point fans directly at buds—bounce air off the tent walls for indirect movement

3. Drop the Humidity (Fast)

• Use a dehumidifier

• Set RH to:

  • 45–50% during mid-flower

  • 35–40% during late flower

• If you're in a tent, keep a digital hygrometer at canopy level

4. Lower Watering Frequency

• Less water = less internal moisture

• Water when the top 1–2 inches of soil feel dry

• Avoid watering late in the day, especially outdoors

5. Trim Inner Growth and Larfy Buds

• Lollipopping and light defoliation help air move through the plant, not just around it

• More airflow = fewer mold-prone pockets

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How to Prevent Bud Rot in the First Place

Prevention is far easier than removal. Here’s how to stay one step ahead:

During Veg:

• Keep RH around 55–65%

• Shape plants early for better airflow

• Use low-stress training (LST) to open the canopy

During Flower:

• Reduce RH as flowering progresses

• Space out plants to prevent overlap

• Install carbon filters or UV-C light sanitizers if you have mold history

• Avoid foliar sprays after week 2 of flower

Harvest Time:

• Harvest on a dry day if you’re growing outdoors

• Never hang wet buds in a humid room—dry in 50% RH, 60°F if possible

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What Happens If You Smoke Bud Rot?

Don’t. Ever.

Bud rot can release spores and mycotoxins that are dangerous to inhale, especially for people with respiratory issues or compromised immune systems. If you find mold—even a little—toss the bud.

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Vigilance Is Victory

Bud rot is sneaky, savage, and heart-wrenching—but not unbeatable. Keep your air dry, your buds spaced, and your nose sharp. The more you understand the conditions that cause bud rot, the more you can tweak your grow to keep it out. Your buds will thank you by staying firm, frosty, and fungus-free.

We’re just a bunch of homegrow nerds who’ve battled our fair share of bud rot—and lived to tell the tale. Now we’re here to help you grow clean, dank, mold-free weed from the comfort of your own space. Check out some of our other tips on our website.