Root Rot in Cannabis Plants
Root rot is a fast-moving, plant-killing disease caused by Pythium or similar oomycetes. Caught early, it's recoverable. Caught late, the plant dies within days.
What it looks like
- ●Droopy, wilting leaves that don't perk up after watering
- ●Yellowing across the whole plant at once
- ●Roots: slimy, brown/tan, fall apart when touched (healthy roots are white and firm)
- ●Swampy, sulfur-like smell from soil or reservoir
Quick diagnostic checks
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of root rot before you change nutrients, watering, or the environment.
VIVOSUN pH and TDS Meter Combo
Check root-zone pH and nutrient strength before changing a feeding plan.
Check price on AmazonVIVOSUN 5-Gallon Fabric Pots
Improve drainage and root-zone oxygen while reducing overwatering risk.
Check price on AmazonApera Instruments PH20 Meter
A more accurate, waterproof pH meter for repeatable root-zone checks.
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Causes ranked by likelihood
1. Overwatering in soil
Most commonSigns
- ●Soil stays wet for 5+ days
- ●No drainage holes or poor drainage
- ●Cold soil temperatures
Fix
- ✓Stop watering immediately — let soil dry out
- ✓Add drainage holes or switch to fabric pots
- ✓Water deeply but infrequently — roots need oxygen
2. Warm reservoir in hydro
Most commonSigns
- ●Reservoir temp above 72°F
- ●DWC/hydro setup
- ●Often appears after a warm spell
Fix
- ✓Get reservoir below 68°F with a chiller or frozen bottles
- ✓Dose H2O2 (3% hydrogen peroxide) at 1 ml/L to kill pathogens (short-term only)
- ✓Long-term fix: add beneficial microbes (Hydroguard, Great White)
Recommended products
Hydroguard Root Inoculant
Beneficial Bacillus bacteria — outcompetes Pythium
3. Compacted soil with no oxygen
CommonSigns
- ●Heavy clay-like soil
- ●No perlite or amendment
Fix
- ✓Transplant to a well-draining mix (30-40% perlite for cannabis)
- ✓If transplant isn't possible, poke aeration holes in soil with a chopstick
⚠️When to worry
Always. Root rot can kill a plant in 3-5 days once it takes hold. Act at the first sign of unexplained wilting that doesn't respond to water.
Gear that prevents this problem
The right equipment stops most grow problems before they start. Start here:
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