Cannabis Leaf Yellowing From Overwatering: Fix Wet Soil

Cannabis leaf yellowing from overwatering: the short answer

Overwatering removes oxygen from the root zone. Roots need oxygen for respiration. Without it, roots cannot pull in water or nutrients. Nitrogen and magnesium move to the leaves first. When uptake stops, the plant pulls nutrients from older leaves. Those lower leaves turn yellow. This starts 3 to 7 days after repeated saturation.

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Symptoms that point to overwatering

• Lower and middle leaves yellow first.
• Leaf blades turn a flat, even yellow. Tips stay green at first.
• Leaves droop and feel soft or limp.
• Soil stays wet 4 or more days after a watering.
• Pot feels heavy when lifted.
• New growth stays small and pale.
• Fungus gnats, algae, or a sour smell in the soil.

Overwatering vs. nutrient deficiency

Nitrogen deficiency also yellows lower leaves. Check the soil. Wet soil plus yellow lower leaves points to overwatering. Dry soil plus yellow lower leaves points to a nutrient problem or pH lockout. Low oxygen causes lockout. Roots cannot absorb nutrients even when the soil holds them. Feeding more does not fix this. It adds salt and stress.

cannabis yellow leaves with brown spots

How to fix an overwatered cannabis plant

1. Stop watering. Wait until the top 2 to 3 inches of soil are dry.
2. Check pot weight. A light pot means dry soil.
3. Empty the saucer. Standing water keeps the root zone saturated.
4. Move air. A small fan across the pot surface speeds evaporation.
5. Hold the root zone at 65 to 75F. Cold, wet soil slows root recovery.
6. Do not feed until new growth shows a normal green color.
7. For mushy, brown roots with a smell, transplant into fresh mix. Cut dead roots with clean shears.

Recovery takes 7 to 14 days. Yellow leaves will not turn green again. Watch new growth for color.

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Prevention

• Water when the top 2 to 3 inches are dry. Test with a finger or a moisture meter.
• Use pots with drainage holes. Fabric pots dry faster.
• Mix 20 to 30 percent perlite into the medium.
• Water to 10 to 20 percent runoff. Then empty the saucer.
• Keep the root zone at 65 to 75F.
• Water less in cool rooms and during late flower.