How to Keep Mulch 10 cm Away From the Tree Trunk

Mulch helps the soil retain moisture and limits competition from weeds, but how it is laid matters too. The Royal Horticultural Society advises keeping a mulch layer on the soil while leaving roughly 10 cm clear around the trunk, as damp material touching the bark directly can encourage decay.

Why should mulch not touch the trunk?

Mulch can stay damp for a considerable period. If it is piled directly against the base of a tree or woody shrub, the bark remains in constant contact with the moist material, which can soften it and make it more susceptible to deterioration.

For this reason, mulch should not look like a heap shaped into a cone around the trunk. Instead, spread it across the soil as a ring, leaving an unmulched space immediately around the base.

How deep should a mulch layer be?

The Royal Horticultural Society recommends a layer at least 5 cm deep and, in various guidance, suggests depths of around 7.5 to 10 cm depending on the application. For home use, a 5 to 8 cm layer is a practical guide within these recommendations.

Suitable mulching materials include well-rotted compost, composted leaves, straw and shredded bark, depending on the intended purpose. As well as helping the soil hold water, mulch can help to suppress the growth of unwanted plants.

How do you create a mulch ring around a tree?

Start by spreading the material evenly over the soil around the plant. Then pull the mulch back from the trunk base to make a clear circle of around 10 cm. This gap helps prevent mulch from remaining in contact with woody stems.

There is also no need to build up a mound of material beside the trunk. An even layer across the root area performs the mulching role more effectively and avoids concentrating moisture around the plant's most sensitive area.

Which plants need the greatest care with this detail?

This precaution is particularly important for trees, shrubs and other plants with woody stems. The same advice applies in gardens where leaves, bark and other organic materials are regularly added to the soil.

If mulch has already built up against the trunk, simply draw it back carefully to create the clear strip. In this way, mulch against the trunk no longer creates the familiar “volcano” and instead works as a protective soil layer, without keeping the base of the plant continually damp.