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DiseaseRootsWhole plantStems

Root rot

The consequence of prolonged waterlogging rather than an independent event: water moulds that are present in most soil and compost become active when roots are deprived of air, and colonise tissue that is already dying. The treatment is therefore the watering, not the fungus.

Caused by: Pythium, Phytophthora and other water moulds · also called root and stem rot, damping off of roots

Nothing available to a home grower will fix this

There is no fungicide available to home gardeners that will cure established root rot. Recovery depends entirely on removing the affected roots and correcting the conditions, and a badly affected plant is often not recoverable.

source

Sourced guidancehigh confidence

  • Royal Horticultural Society: Root rots — control

Checked 2026-08-13

Described view

A young plum tree in leaf showing root rot above ground and below: sparse yellowing foliage thinning from the lower branches upward with no insect or lesion on the leaves, and the base of the trunk excavated to show dark, soft, sour-smelling roots that strip to a discoloured core

What brings it on

Compost or soil kept saturated, poor drainage, a pot standing in water, or cold wet conditions where the plant is not transpiring. Cool and wet together is much worse than either alone.

source

Sourced guidancehigh confidence

  • Royal Horticultural Society: Root rots

Checked 2026-08-13

Preventing it

Ordered by how much difference each measure actually makes, not by how often it is repeated.

  • Manage the water rather than the organism. Free-draining compost, a pot with drainage holes that are not blocked, and an emptied saucer prevent nearly all of it.
    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Root rots

    Checked 2026-08-13

Dealing with it once it is there

  • Tip the plant out and inspect. Firm pale roots are healthy; brown, soft roots that slough their outer layer when pulled are rotten. Cut rotten roots back to healthy tissue, repot into fresh free-draining compost in a pot no larger than the remaining root ball needs, and keep it barely moist until it recovers.
    source

    Sourced guidancehigh confidence

    • Royal Horticultural Society: Root rots

    Checked 2026-08-13

On sprays and treatments

GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.

Plant-specific guides

Where this is one of several causes that look alike on a particular plant, GrowingHQ publishes the differential rather than the general answer.