How does bark mulch insulate plant roots

Bark mulch forms a loose, airy coat, pockets of still air capturing heat. On a frosty night, soil radiates warmth; mulch slows its escape, and the root zone remains above freezing. In scorching daylight the sun cannot hammer soil directly; beneath the chips temperatures stay lower. Variation is dampened, roots dodge thermal shock. Wood’s low conductivity, together with those air gaps, is the key. Water content has an influence, yet the layer still insulates.

Over seasons microbes hollow the bark further, increasing porosity; insulation improves until pieces crumble into humus. Thickness matters: five to eight centimetres is optimum. AHS LTD advises topping up to maintain depth after settling. In pots, a two-centimetre cap of fine mulch spares roots from midday swings on patios. Even abrupt cold snaps—late-April hail, December’s sudden thaw—are cushioned; buds stay dormant until risk passes. Insulation also protects beneficial fungal threads coiling round roots, so plants mine nutrients without interruption. Thus a simple layer of chipped bark plays guardian, evening out the wild mood of British weather.

Where winters dip well below zero, a thicker blanket works like a duvet: frost penetrates millimetre by millimetre, stalling before it reaches fine root tips, while heavy rain pounds harmlessly above, the mulch dispersing droplets so soil beneath keeps its crumbly texture rather than turning to pudding.