Identium
Root Rot: How to Tell If It Is Too Late, and How to Save It If Not
Firm and pale means alive. Brown and slimy means gone. Everything else follows from that one distinction.
Root rot is the leading cause of houseplant death, and it is almost always the end point of a watering habit rather than an infection that arrived from outside.
The fungi involved are already in the soil. They are opportunists that move into root tissue after it has died. What kills the roots first is a lack of oxygen.
Why waterlogged soil kills
Roots respire. They take in oxygen through the air gaps between soil particles.
Keep soil saturated and those gaps stay full of water. The roots suffocate and begin to die back. Dead root tissue is then colonised by soil fungi, which spread into neighbouring tissue that is already weakened, and the process accelerates.
The cruel part is the symptom. A plant with fewer working roots cannot take up water, so it wilts. The owner sees wilting, waters it, and the problem compounds. Most plants lost to root rot were watered enthusiastically right to the end.
A plant wilting in damp soil is not thirsty. It has lost the roots it needs to drink with.
Rule of thumbThe signs, above soil
- Wilting or drooping while the soil is damp
- Lower leaves yellowing and dropping, working upward
- Soil that stays wet for many days after watering
- A sour, swampy or sulphurous smell from the pot
- Stem soft or squishy at the soil line
- Growth stopped entirely for no other reason
- Fungus gnats, which need permanently damp soil
None of these is conclusive on its own. The only way to know is to look at the roots, and people put that off because it feels drastic. It is not. Tipping a plant out of its pot is a routine health check that takes two minutes.
What roots should look like
Healthy: firm, pale, white to tan, sometimes with fine hairs. They resist when you tug them and snap rather than smear.
Rotted: brown or black, soft, slimy. The outer layer slides off between your fingers leaving a thin thread behind. They smell.
That sliding outer layer is the definitive test. Healthy roots do not do it.
Is it salvageable?
Two questions decide it.
Is there any firm root left? If you can find a reasonable amount of pale firm root after cutting away the rot, the plant has something to rebuild from.
Is the stem still firm? Squeeze the base. If the stem is soft or mushy above the soil line, the rot has moved into the plant itself and cutting roots will not save it.
If the stem is firm and some root remains, proceed. If the stem is mushy through, stop trying to save the plant and take cuttings from healthy top growth instead. Pothos, philodendron, monstera and most vining plants root readily and you keep the plant even if you lose the specimen.
The rescue
- Tip it out. Support the stem base, invert the pot, squeeze or tap. Never pull by the stem.Step 1
- Wash the old soil off the roots under a gentle tap so you can see what you have.Step 2
- Cut away every brown, soft or slimy root with clean scissors. Be ruthless. Leaving rot behind restarts everything. Sterilise the blades between cuts.Step 3
- Reduce the foliage to match. If you removed a third of the roots, remove roughly a third of the leaves. The remaining roots cannot support the old canopy.Step 4
- Repot into fresh dry mix, in a pot sized for the roots you have left, not the ones you started with. Add perlite or bark to open it up.Step 5
- Do not water for three to five days, then water lightly. Damaged roots need air more than water.Step 6
- Bright indirect light, no direct sun, no fertiliser. Feeding damaged roots makes things worse.Step 7
Do not reuse the old soil, and wash the pot before reusing it.
What recovery looks like
Two to six weeks before you can judge anything. The leaves that were already yellow will not recover, so ignore them.
What you are watching for is new growth. That is the plant telling you it has rebuilt enough root to start working. Until then it is neither improving nor failing, it is rebuilding, and the temptation to intervene again is what kills a lot of otherwise successful rescues.
Prevention, which is four things
A drainage hole. Not optional. If you love a pot without one, keep the plant in a plastic nursery pot and drop it inside.
Empty the saucer. A pot standing in water never dries.
Right sized pot. An oversized pot holds a mass of wet soil the roots cannot reach or use, and that is the most common cause of rot after repotting.
Check before watering. Finger two inches down every time. Adjust for season, since a pot that dries in five days in July can take three weeks in January.
The signs of root rot look identical to underwatering from above, and getting that wrong doubles the damage. Photograph the plant and the soil surface and Identium will help you work out which way round it is before you water again.
Frequently asked questions
How do I know if my plant has root rot?
Tip it out of the pot and look. Healthy roots are firm and pale, white to tan, and snap when pulled. Rotted roots are brown or black, soft and slimy, and the outer layer slides off between your fingers leaving a thread behind. A sour smell from the pot is another strong sign.
Can a plant recover from root rot?
Often, if the stem is still firm and some pale firm root remains. Cut away every soft or discoloured root, reduce the foliage to match what is left, repot into fresh dry mix in an appropriately sized pot, and wait three to five days before watering lightly. Expect two to six weeks before new growth appears.
Why does my plant wilt even though the soil is wet?
Because it has lost the roots it needs to take up water. Waterlogged soil has no air gaps, so roots suffocate and die back, and a plant with fewer working roots cannot drink even when surrounded by water. Watering it again at that point makes it worse, which is how most root rot cases end.
Should I use a fungicide for root rot?
Usually not necessary. The fungi involved are already in the soil and move in after roots die from lack of oxygen, so removing the rotted tissue and fixing the drainage addresses the cause. Fresh dry mix, a correctly sized pot and restrained watering do more than any product.
How do I stop root rot happening again?
Use a pot with a drainage hole, empty the saucer after watering, do not go up more than one pot size at a time, and check the soil two inches down before every watering rather than following a schedule. Adjust for season, since winter watering intervals can be three times longer than summer.