Plant diseases

Root rot: symptoms, causes and how to save the plant

Complete guide to root rot in houseplants: how to recognise it, typical causes, how to intervene and how to prevent it.

Updated on 2026-07-14 · 8 min read

Root rot is the number-one killer of houseplants. In most cases it isn't the fault of an especially aggressive fungus, but of a simple and repeated mistake: overwatering, or watering in a pot that can't drain. In this guide we'll see how to spot rot at the earliest signals, how to intervene to save the plant, and how to set up conditions that make the problem practically impossible.

What root rot is

Root rot is the decomposition of the roots caused by soil-borne pathogenic fungi — most commonly Pythium, Phytophthora, Fusarium and Rhizoctonia. These fungi are almost everywhere, but they only become a problem when they find the right environment to multiply: a substrate that stays constantly saturated with water, low oxygen at the roots, mild temperatures.

The mechanism is always the same: starved of oxygen, the roots weaken and fungi colonise them. The plant loses the ability to absorb water and nutrients — and paradoxically starts showing symptoms of water shortage even though the soil is wet.

Typical symptoms

Root rot shows up on the visible part of the plant long before it shows on the roots. Here are the most reliable signs:

  • Leaves yellowing from the bottom up, often several at once.
  • Soft or blackened stem at the base, with a sour or rotten-egg smell up close.
  • Leaves that fall off at the slightest touch, even apparently healthy ones.
  • Substrate that stays wet for days after watering.
  • Roots, if you slide the plant out of the pot, that look dark (brown or black), mushy, stringy and pull off easily. Healthy roots are pale white or cream and firm.

The most common causes

In most cases rot arises from a combination of these factors:

  • Watering too frequently: the wet-then-dry cycle is essential for root health.
  • Pot with no drainage hole, or a saucer that pools stagnant water for days.
  • Substrate that's too dense or compacted, choking the roots.
  • Pot that's too large for the plant: excess substrate stays wet without being used.
  • Low temperatures (below 15°C) combined with normal watering: the plant uses less water and the substrate never dries.
  • Cold or stagnant water that encourages fungal growth.

How to intervene: step-by-step protocol

If you suspect root rot, act today. Time is the variable that decides whether you save the plant or not.

  • 1) Gently slide the plant out of the pot and inspect the roots. If they're all black and mushy, the plant is very compromised. If there's still a firm white portion, it can be saved.
  • 2) With sterilised scissors (wiped with alcohol or briefly held over a flame), cut off all rotten roots back to healthy tissue.
  • 3) Rinse the remaining roots under lukewarm running water to wash away contaminated substrate and fungal spores.
  • 4) Let the roots air-dry for 1-2 hours on kitchen paper. Some people dust them with ground cinnamon (a mild natural antifungal) or use a systemic fungicide in severe cases.
  • 5) Repot in a clean container with entirely new, well-draining substrate suited to the species. The pot must have proper drainage holes and shouldn't be oversized: 2-3 cm larger than the rootball is enough.
  • 6) Water very sparingly for 2-3 weeks. With fewer roots, the plant uses less water. Resume the normal rhythm only when you see new growth.
  • 7) Keep the plant in bright indirect light, mild temperatures (18-22°C) and away from cold drafts while it recovers.

Prevention

Preventing rot is almost always easier than curing it. The golden rules:

  • Always use pots with a drainage hole. If a decorative pot has none, keep the plant in a plastic inner pot with holes.
  • Empty the saucer 15-30 minutes after every watering.
  • Before watering, stick a finger into the soil: if the top 2-3 cm is still moist, wait. In winter many plants want to dry almost completely between waterings.
  • Pick the right substrate: all-purpose with perlite for most plants, specific mixes for succulents or orchids where required.
  • Don't repot into oversized pots. Small gradual size steps are safer.
  • In winter, cut watering by 30-50% compared to summer.

When it's too late

If all the roots are rotten, the stem is mushy all the way up and the plant separates from the base at the slightest touch, the rot is generalised and the plant can't be saved as a whole. You can still try propagation: if any leaves or stem sections are still healthy, cut a 10-15 cm cutting, let it dry for 24 hours and place it in water or moist perlite to root. Many houseplants (pothos, monstera, philodendrons, snake plant) regenerate easily from cuttings, giving you a second chance even when the parent is lost.

When to ask for help

If you've already repotted correctly and symptoms return within days, there may be a deeper issue: contaminated substrate, a persistent pathogen or wrong environmental conditions. Take a photo of the plant and roots and upload it to Botanix for a contextualised diagnosis, or bring the plant to a specialist nursery for a hands-on opinion.