Root rot in houseplants: signs, causes and what to do

What causes root rot

Several fungi and fungus-like organisms cause root rot, including Pythium, Phytophthora, Rhizoctonia and Fusarium. They usually take hold after a plant has been stressed, most often by overwatering or poor drainage. Iowa State University Extension: root rots of houseplants

Pythium spreads through water: its spores can swim towards roots in a film of water, which is why constantly wet mix and dirty pots and tools matter. Utah State University Extension: Pythium root rot

Waterlogging alone also damages roots, and its symptoms look much the same. The RHS notes that Phytophthora is primarily a problem of heavy or waterlogged conditions. A home grower cannot tell these organisms apart by eye, and does not need to: the first response is the same. RHS: Phytophthora root rot

Signs above the soil

• Wilting while the mix is still damp, often starting with lower leaves
• Yellowing leaves and slower growth
• A stem base that darkens or softens
• Mix that stays wet for days and may smell sour

University of Maryland Extension describes stunting, yellowing and wilting even when the mix moisture is adequate. These signs overlap with underwatering, cold and pests, so do not diagnose from leaves alone. University of Maryland Extension: root rots of indoor plants Start with the checks in overwatered or underwatered?

How to check the roots

Healthy roots are usually firm and white or pale, often with many fine feeder roots. Rotted roots are mushy and brown or reddish. Iowa State University Extension: root rots of houseplants In bad cases the outer layer of a root slips off when you pull gently, leaving a thin thread, and much of the root system stays behind in the pot. University of Maryland Extension: root rots of indoor plants

What to do if you find rot

1. Work over newspaper. Remove the old, wet mix from around the roots.
2. Cut away soft, brown roots back to firm tissue with clean scissors or secateurs.
3. Choose a clean pot with a drainage hole, no bigger than the remaining roots need. A pot much larger than the root system holds extra wet mix.
4. Repot in fresh potting mix for houseplants, at the same depth as before. Do not reuse the old mix. Clemson Cooperative Extension: repotting indoor plants
5. Water once lightly to settle the mix, let it drain, then wait until the mix has dried to a suitable level before watering again.
6. Keep the plant in good indirect light, out of cold draughts, and do not fertilise until new growth appears.
7. Wash the old pot and tools before using them again. Utah State University Extension: Pythium root rot

If almost every root is rotten, recovery is unlikely, and discarding the plant with its mix is often the practical choice. If a stem still has firm, healthy growth, a cutting may give you a new plant; see propagating houseplants from cuttings.

We do not suggest fungicide treatments here. Products and their approval differ by country; if you consider one, use only a product labelled for houseplants and follow the label exactly.

How to prevent it next time

• Water when the mix needs it, not by calendar. Our watering guide shows how to check.
• Use a pot with a drainage hole and empty saucers and outer pots after watering.
• Use a free-draining mix suited to the plant; see potting mix and drainage.
• Expect slower drying in winter light and cool rooms.
• Repot into a modestly larger pot when roots need it, as described in when to repot.

Writing down each check helps here. In Lilora, "Checked, no water needed" and "Watered" are separate records, so a pot that stayed wet for ten days shows up as a run of checks rather than disappearing from memory.

Common questions

Can root rot spread to my other plants?

The organisms can travel in water, mix and on tools. Keep the affected plant's saucer separate and clean pots and tools before reuse. Utah State University Extension: Pythium root rot

Should I let the root ball dry out in the air?

Do not leave roots exposed for long. Trim, repot in fresh mix, and control moisture from then on.

My plant wilts but the roots look fine. What now?

Then root rot is unlikely. Check light, temperature, pests and recent changes; see yellow houseplant leaves.

Is hydrogen peroxide a good treatment?

We could not find institutional guidance with a safe home dose, so we do not recommend one.