Root Rot
Act nowFungal disease · does not spread · also called phytophthora, pythium, overwatering rot
Root rot is the commonest killer of houseplants and container plants, and it is caused by soil staying wet rather than by watering too often. Waterlogged soil has no oxygen, roots suffocate and die, and opportunistic fungi move into the dead tissue. The plant then wilts because it has no functioning roots — which looks exactly like thirst, so people water more.
What it looks like
Above ground, yellowing and wilting that looks like drought but does not respond to water. Below ground, roots that are brown or black, soft, and smell sour — healthy roots are firm and pale, and the outer sheath of a rotted root slides off leaving a thread.
How to confirm it
- Wilting that does not improve after watering, and often gets worse.
- Roots brown or black, soft, and easily pulled apart. Healthy roots are firm and light.
- A sour or swampy smell from the pot.
- Soil still damp days after watering.
What to do
- 1Take the plant out of the pot and look at the roots. This is the only way to confirm it, and it is what almost nobody does.
- 2Cut away every soft brown root with clean scissors, back to firm tissue.
- 3Repot into fresh, free-draining mix in a pot with a drainage hole — ideally a size smaller, since an oversized pot holds too much water.
- 4Water sparingly until new growth appears, and never let the pot stand in a full saucer.
What it gets confused with
One observation settles each of these.
Check the soil. A thirsty plant has dry, shrinking soil and perks up within hours of a soak; a rotted plant has wet soil and gets worse.
Fusarium shows brown staining inside the stem's vascular ring; root rot shows mush at the roots.
Preventing it next time
- Water when the top inch or two of the mix is dry, not on a fixed schedule.
- Use pots with drainage holes. A layer of gravel in the base does not substitute for one.
- Match pot size to root size, and use a mix that drains freely.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.