Root rot: brown, slimy roots
Roots should be white and firm. Brown, slimy or foul-smelling roots mean the root system is drowning, and the plant above will follow within days.
What you see
Lift the net pot and look at the roots. Healthy roots in a DWC system are white or cream, branching and firm. Diseased roots are brown, mushy, stripped of their outer layer, and smell of rot.
Above the pot the plant wilts during the day and recovers at night, then stops recovering. Leaves yellow from the bottom up. Growth stops entirely.
Why it happens
Not enough dissolved oxygen
The defining cause. Roots submerged in still, warm water cannot respire and begin to die. This is what the air pump and airstone prevent, and why a failed pump is an emergency rather than an inconvenience.
Water too warm
Warm water holds less dissolved oxygen and favours the pathogens that cause rot. Above about 24 °C in the reservoir, root problems become likely regardless of how good the pump is.
Water level too high
If the waterline covers the net pot or the crown of the plant, the stem sits permanently wet. The crown rots first, then the plant collapses.
Organic matter in the reservoir
Dead roots, fallen leaves or algae in the water decompose and consume the oxygen the living roots need.
What to do
Check the pump first. Every time. A blocked airstone or a failed pump is the most common cause and the fastest to fix. You should see visible bubbling across the surface.
- Lower the water level. Two to three centimetres below the net pot, so the crown stays dry and the roots reach down for water.
- Cool the reservoir to 18–20 °C. This raises dissolved oxygen and slows pathogen growth.
- Trim dead roots with clean scissors — the brown, mushy ones. They will not recover and they consume oxygen as they decay.
- Change the reservoir completely and clean it. Do not just top up.
- Remove any organic debris — fallen leaves, algae, dead root fragments.
Root rot after a pump failure — is the plant ever recoverable?
Pump failed overnight. Roots are brown but the plant is still standing.
All problems
Six things go wrong in a small reservoir. The index covers each.