Root Rot on Your Houseplants? Here's How to Manage It

Root rot is the most common way that we see houseplants die, and it is almost always manageable if you catch it early.

It is not a single pest but a group of problems: soil-borne fungi and water moulds that attack roots left sitting in wet, airless compost.

The good news is that a plant with some healthy root left can usually be saved by acting quickly! This guide explores our tried-and-tested methods.

What is root rot?

Root rot is the decay of a plant's root system, driven by pathogens that thrive in waterlogged soil. Healthy roots are firm and pale. Rotten roots turn brown or black, feel soft and mushy, and often slide apart when you touch them. Once the roots fail, the plant can no longer take up water or nutrients, which is why a rotting plant often looks, confusingly, like a thirsty one.

What causes root rot on houseplants?

The root cause is overwatering and poor drainage, which starve the roots of oxygen and create the conditions the pathogens need. The usual culprits are:

• Pythium and Phytophthora, water moulds that spread fast in saturated compost.
• Rhizoctonia and Fusarium, soil fungi that move in on weakened roots.

These organisms are often already present in small numbers. They only become a problem when a pot stays wet: heavy compost, no drainage holes, a pot that is too large, or simply watering on a schedule rather than checking the soil first. For the fuller picture on the watering side, see our tip on the signs of overwatering.

How do I know if my houseplant has root rot?

Above the Soil

Watch for yellowing lower leaves, wilting that does not recover after watering, soft or blackened stem bases, stunted growth, and a persistent damp, sour smell from the compost. These signs overlap with underwatering, so always check the roots before deciding.

Below the Soil

Slide the plant out of its pot. Healthy roots are firm and white or tan. Rotten roots are brown to black, slimy, and pull away easily, sometimes leaving the outer sheath behind like a wet sock. A rotten rootball frequently smells of stagnant water.

What damage does root rot cause on houseplants?

As roots die, the plant loses its ability to draw up water and feed itself. Foliage yellows, wilts and drops, growth stalls, and in advanced cases the rot creeps up into the crown and stem, at which point the plant cannot be saved. Caught early, while firm root remains, most plants recover.

How do I get rid of root rot?

Immediate Steps

1. Remove the plant from its pot and gently wash the compost off the roots so you can see what you are dealing with.
2. With clean, sharp scissors, trim away every soft, brown or black root. Cut back to firm, pale tissue. Sterilise the blades between cuts so you are not spreading the pathogen.
3. Remove any yellow or collapsed leaves. A plant with fewer roots cannot support a full canopy.
4. Repot into fresh, free-draining compost in a clean pot with drainage holes, ideally one size smaller if you removed a lot of root.

Substrate and Drainage

The repot is where you fix the underlying cause. Use a light, airy mix rather than dense, water-retentive compost. Our peat-free Simply Houseplant mix with extra coarse perlite gives roots the air they need to recover. For chunky aroids, our range of GrowTropicals substrates has mixes built around drainage. Always use a pot with drainage holes; decorative pots without them are a common hidden cause.

Watering After Treatment

Water the repotted plant in, then hold back. Let the top few centimetres of the new mix dry before watering again, and keep the plant somewhere warm and bright but out of harsh sun while it rebuilds roots. A moisture meter or the simple finger test, from our plant care range, takes the guesswork out. Recovery is slow, so do not be tempted to overwater to help it along.

How can I prevent root rot on my houseplants?

Prevention comes down to water and air at the roots.

• Water only when the top 2 to 5 cm of compost is dry. Check first, every time.
• Always use pots with drainage holes and empty the saucer after watering.
• Match pot size to the plant. Oversized pots hold water the roots are not using.
• Use a free-draining mix suited to the plant rather than dense general compost.
• Ease off watering in winter, when plants use far less.

And as always, if you need any plant care tips feel free to email our team!