Root rot is the decay of a plant’s roots, usually caused by soil that stays wet for too long, which starves roots of oxygen and lets water moulds such as Pythium and Phytophthora attack them. Signs include yellowing leaves, wilting even though the soil is wet, a soft stem base and a sour smell. To treat it, remove the plant from its pot, cut away all brown, mushy roots, and repot in fresh, free-draining mix in a clean pot with drainage holes. Then water only when the top of the soil is dry.
Root rot is one of the most common reasons houseplants decline, and one of the most preventable. This guide explains what root rot is, what causes it, how to spot it above and below the soil, how to treat it step by step, and how to stop it happening again.
At Patch Plants, botanist Sawera Shahid sums up root rot in one line: roots need air as much as water. Almost every case comes down to soil that never gets the chance to breathe between waterings. Read more about how we write our guides on the About Patch Plants page.
Key Takeaways
- Root rot starts when soil stays waterlogged, roots run short of oxygen and rot organisms take hold.
- Overwatering, pots without drainage holes, dense or old compost and pots that are too big are the main causes.
- Above the soil, look for yellowing, wilting in wet soil, a soft stem base and a sour smell.
- Healthy roots are firm and white or tan; rotten roots are brown or black, mushy and smelly.
- Treat by trimming rotten roots and repotting in fresh mix; hydrogen peroxide is optional, not a cure.
- If most of the roots are rotten, take cuttings from healthy stems instead.
- Prevent it with drainage holes, the right mix and watering only when the soil needs it.
What Is Root Rot?
Roots need both water and air. In free-draining soil, water runs through and air refills the spaces between soil particles. When soil stays wet for days, those spaces stay full of water, roots can’t breathe and start to die back. Weak, dying roots are then easily invaded by soil-borne organisms, mainly water moulds (oomycetes) such as Pythium and Phytophthora, and sometimes fungi such as Rhizoctonia and Fusarium. These spread through wet soil from root to root.
Clemson Cooperative Extension notes that too much water reduces the oxygen roots need and favours root diseases, and that yellowing of a whole plant is most often caused by overwatering. In other words, root rot is usually a care problem first and a disease problem second.
What Causes Root Rot?
| Cause | Why it leads to root rot |
|---|---|
| Overwatering | Watering on a schedule before the soil has dried keeps roots permanently wet |
| No drainage holes | Water collects in the bottom of the pot and saturates the lower roots |
| Dense or old compost | Compost breaks down and compacts over time, holding more water and less air |
| Pot too big | Extra soil the roots can’t reach stays wet for too long |
| Standing water in saucers | The soil soaks water back up from below |
| Cold, low light, winter | Plants use less water, so soil dries much more slowly |
| Contaminated soil or pots | Reused compost or dirty pots can carry rot organisms |
See our guides to signs of overwatering and the best soil mix for every type of plant.
Signs of Root Rot
Above the Soil
- Yellowing leaves, often starting with lower leaves and spreading.
- Wilting or drooping even though the soil is wet: damaged roots can’t take up water.
- Slow or no growth, and new leaves smaller than usual.
- Leaf drop, sometimes without yellowing first.
- A soft, dark or mushy stem base.
- A sour or rotten smell from the soil.
- Soil that stays wet for a week or more after watering, often with fungus gnats.
Below the Soil: Healthy Roots vs Root Rot
| Healthy roots | Rotten roots |
|---|---|
| Firm and springy when squeezed | Soft, mushy or slimy |
| White, cream or light tan (some plants have orange or brown healthy roots) | Dark brown or black, often with a sloughing outer layer |
| Earthy smell | Sour or rotten smell |
| Hold together when handled | Outer skin slides off, leaving a thin thread |
See our photo guide to healthy roots vs root rot for more examples.
How to Treat Root Rot Step by Step
- Take the plant out of its pot. Tip the pot and ease the root ball out; run a knife around the inside if it sticks. Don’t pull on the stem.
- Remove the old soil. Gently shake or rinse it away with lukewarm water so you can see all the roots. Throw this soil away.
- Assess the damage. Work out roughly how much of the root system is healthy and how much is rotten.
- Cut out all rotten roots. Using scissors cleaned with rubbing alcohol, cut back to firm, healthy tissue. Clean the blades again between cuts if rot is severe. If you remove a lot of roots, also trim some leaves so the plant has less foliage to support.
- Let the roots air dry briefly. Leave them on newspaper for 30 minutes to an hour. Succulents and cacti can be left for a day or two to let cuts callus.
- Repot in fresh mix. Use new, free-draining potting mix suited to the plant, in a clean pot with drainage holes that is only just big enough for the remaining roots. Disinfect an old pot before reusing it.
- Water lightly and wait. Give just enough water to settle the mix (wait a few days for succulents), then let the top few centimetres dry before watering again. Keep the plant in bright, indirect light, away from cold draughts.
- Don’t feed until you see healthy new growth, usually four to eight weeks later.
New leaves after a few weeks show the plant has recovered. See our guides on how to repot a plant, repotting mistakes to avoid and how to revive a dying plant.
Does Hydrogen Peroxide Help Root Rot?
Hydrogen peroxide is a popular home remedy. Some growers rinse trimmed roots in a solution of one part standard 3% hydrogen peroxide to about four parts water before repotting, to clean them. If you try it, use it once, at that low strength, and only on roots you have already trimmed. Stronger solutions or repeated use can damage healthy root tips.
It is not a cure on its own. The things that actually save a plant with root rot are removing the rotten roots, fresh free-draining mix, a pot with drainage and better watering. Hydrogen peroxide can’t fix soil that stays waterlogged.
What About Fungicides?
For most houseplants, fungicides aren’t needed: Clemson Extension notes that they usually cost more than replacing the plant. For valuable outdoor plants or repeated problems, ask a garden centre for a product specifically labelled for Pythium or Phytophthora root rot on that type of plant, and follow the label exactly. These organisms are not true fungi, so many general fungicides don’t control them.
Root Rot in Popular Houseplants
- Snake plant and ZZ plant: rot often shows as soft, yellow or brown leaf bases or mushy rhizomes. These plants hide it for a long time, so check the base if they look unhappy.
- Pothos and philodendron: yellow leaves appear quickly; healthy stems can be rooted in water if most roots are lost.
- Monstera: large leaves can look fine while roots decline in an oversized pot.
- Peace lily: drooping can mean too dry or too wet; always check the soil before watering.
- Orchids: healthy roots are plump and silvery-green; rotten ones are brown, flat and hollow. Use bark, never soil.
- Succulents and cacti: often look fine until they suddenly collapse or the base turns soft and dark.
- Money tree: yellowing leaves and soft trunks at soil level.
How to Prevent Root Rot
- Always use pots with drainage holes. Keep plants in plastic nursery pots inside decorative pots without holes.
- Water by need, not by calendar. Check the soil first; most houseplants need water when the top 2–5 cm is dry, succulents only when dry throughout. See our complete watering guide.
- Empty saucers 10–15 minutes after watering.
- Use the right mix and add perlite, bark or grit to heavy compost.
- Choose the right pot size: only 2–5 cm wider than the root ball when repotting.
- Water much less in winter, when light and growth slow down.
- Refresh old compost every one to two years, and don’t reuse soil from a plant that had rot.
- Give plants enough light so they use water at a healthy rate; see our guide to indoor light.
Root Rot in Outdoor Plants
In gardens, root rot is most common in heavy clay soil, low spots where water collects, overwatered beds and containers without drainage. Improve drainage by digging in organic matter, using raised beds, avoiding watering already-wet soil and choosing plants suited to your conditions. See our guides to drought-resistant plants, hardy outdoor plants and keeping outdoor plants alive.
When a Plant Can’t Be Saved
If almost all of the roots are rotten, the stem is soft well above the soil, or the plant keeps declining after treatment, it is unlikely to recover. Before you give up, take cuttings from any firm, healthy stems or leaves; many houseplants root easily in water or fresh mix. Our propagation guide explains how. Bin, rather than compost, the old soil and diseased roots.
Frequently Asked Questions
What does root rot look like?
Rotten roots are brown or black, soft and mushy, often slimy, and smell sour; the outer layer may slide off. Healthy roots are firm and usually white, cream or tan. Above the soil, look for yellowing, wilting in wet soil and a soft stem base.
Can a plant recover from root rot?
Yes, if you act early and enough healthy roots remain. Cut away all rotten roots, repot in fresh, free-draining mix in a pot with drainage holes, and water less often. If most roots have rotted, take cuttings instead.
What causes root rot in houseplants?
Mainly soil that stays wet for too long, from overwatering, pots without drainage, dense or old compost, oversized pots or saucers full of water. Waterlogged roots lose oxygen and are attacked by rot organisms such as Pythium.
Should I use hydrogen peroxide for root rot?
It’s optional. A single rinse of trimmed roots in one part 3% hydrogen peroxide to about four parts water may help clean them, but it doesn’t cure root rot. Trimming rotten roots, fresh mix and better watering are what matter.
How do I prevent root rot?
Use pots with drainage holes, a free-draining mix suited to the plant, and a pot that isn’t too big. Water only when the soil needs it, empty saucers and water less in winter.
Final Thoughts
Root rot is discouraging, but it teaches the most important lesson in plant care: roots need air as well as water. Catch it early, cut away the damage, repot into fresh mix and water by need rather than by habit, and most plants recover. For related problems, see our guides to why leaves turn yellow and leaf curl, browning and droop.
