How does bark mulch affect plant growth

Bark mulch influences plant growth from several angles, some immediate, others unfolding over seasons. When spread five centimetres deep, it seals moisture where roots can sip it, trimming midday wilts and freeing plants to photosynthesise rather than fight drought. The layer also muffles weed seedlings that would otherwise steal light, water and nutrients; with competition muted, garden favourites channel energy into foliage and fruit. Soil beneath stays friable, as pounding rain no longer compacts pores, so roots wander further and draw on a wider pantry of minerals.

Chemical change arrives more slowly. As fungi and bacteria digest lignin, they leak humic acids that chelate trace elements, making iron, zinc and manganese easier for roots to absorb. Nitrogen can be tied up briefly at the mulch–soil interface, but adding a handful of well-rotted compost or manure before laying bark offsets the hitch. Over two or three years, shredded chips mellow into crumbly humus, lifting organic matter and cation exchange capacity, which together underpin steady, resilient growth.

AHS LTD advises refreshing the mulch annually to maintain depth and texture; doing so keeps moisture regulation sharp and ensures a rolling supply of slow-release nutrients. Plants respond with thicker stems, richer leaf colour and more reliable flowering across the calendar.