How do I tell if my plant has root rot, and can I save it?

Root rot is the commonest single cause of houseplant death and one of the commonest in containers outdoors, and it is invisible until you look. Everything above ground says drought — wilting, yellowing, leaf drop — which is why people water more and finish the plant off.

Step by step

1. Take the plant out of the pot.Support the stem between your fingers, tip the pot over and slide it off. If it is stuck, run a knife around the inside or squeeze a plastic pot. Do this before any other treatment, because it answers the question and nothing else does.
2. Look at the roots and the compost together.Healthy: the compost holds together as a block, the roots are firm, pale cream, springy, with bright white tips visible at the outside and base, and it smells of nothing much. Rotted: the compost is dark and sodden and slumps apart, and the roots are brown or grey-black, limp and flattened.
3. Do the sleeve test.Take a root between finger and thumb and pull gently along it. On a rotted root the soft outer layer slides off and leaves a bare central thread behind, like pulling a wire out of its insulation. On a healthy root nothing comes away. This is definitive and takes two seconds.
4. Use your nose.Sour, stagnant, drain-like. Healthy compost smells earthy or of nothing. A distinct bad smell from a pot is confirmation on its own.
5. Understand why it happened, because that decides the repair.Roots need air in the spaces between compost particles. Saturated compost has none, the roots suffocate and die, and the dead tissue is then colonised by water moulds. Once the roots are dead they cannot take up water at all, which is exactly why the plant wilts and why adding water kills it faster.
6. Identify the actual cause of the saturation.A pot with no drainage hole, a blocked hole, a decorative outer pot holding water, a saucer never emptied, a pot far too large for the plant, a compost that has broken down to a dense sludge, or simply watering on a schedule rather than by checking. Fix it or the replacement plant does the same.
7. Wash the roots and cut back to firm tissue.Rinse all the old compost off. With clean secateurs or scissors, cut away every root that is soft, brown or hollow, back to firm pale tissue. Be thorough — leaving rotted material is the main reason a salvage fails.
8. Reduce the top growth to match.If you removed half the roots, take off roughly half the foliage. The remaining roots cannot supply a full canopy, and cutting back is not optional if a lot came away.
9. Repot small, and into fresh compost.A pot only just big enough for the remaining roots, with a clear drainage hole, and fresh compost with added grit or perlite for open structure. A big pot of wet compost around a small root system recreates the problem immediately.
10. Water once, then leave it alone.Water it in, put it out of direct sun and out of draughts, and then wait. Do not feed for at least a month — fertiliser on damaged roots is the classic second injury. Judge recovery only by new growth.
11. Recognise when it is over.If almost nothing firm remains, no technique rebuilds it. Take cuttings from any healthy top growth, compost the plant, and start again. That is the right answer more often than gardeners like to accept.

Tips

• Checking the roots is a diagnostic step, not a last resort. Any container plant that is wilting, yellowing or static should come out of its pot within the first five minutes.
• Water by weight. Lift the pot after watering and again a few days later — the difference is far more reliable than looking at the surface, especially with peat-free compost.
• Never leave a pot standing in a full saucer or a cache pot. Empty it twenty minutes after watering.
• In the garden, the equivalent test is to dig a hole and see whether water stands in it. Root rot in a border is a drainage problem, not a watering one.

Common mistakes

• Watering a wilting plant without checking the compost — Overwatering produces identical wilting, and adding water to saturated compost accelerates the collapse.
• Repotting into a much larger pot to give it room to recover — The surplus compost stays wet and the surviving roots rot too. Small pot, fresh compost, good drainage.
• Feeding after a repot to help it recover — New and damaged roots scorch easily and fresh compost already carries several weeks of feed. Wait a month.
• Keeping the rotted compost because it was expensive — It is dense, airless and full of the organisms that did the damage. Discard it and do not reuse it for pots.

If it doesn't work

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