Mulch offers numerous benefits. If the mulch is organic, work it into the soil after it has broken down to improve soil structure.

Soil structure: crusting

Mulch prevents crusting of the soil surface, thus improving absorption and percolation of water into the soil and reducing erosion. Soil crusting not only prevents water and nutrients from entering the soil, it creates conditions that are extremely conducive to erosion during subsequent rainfall events.

VICAIRE: Groundwater Hydrology, Module 1b Factors influencing infiltration

How do crusts form? Raindrops can reach speeds of 20mph, and splashes detach particles that fill soil pores. When rapid drying occurs, a hard crust layer can form in the top 2 inches of the soil.

3rd Australian New Zealand Soils Conference, Symposium 14 Soil aggregation and structural quality

Soil moisture

The type of mulch is relatively unimportant. All those tested below reduced moisture fluctuation relative to no mulch.

WA CES “The Garden Professors” Bridging Research and Reality

Soil temperature

Mulch moderates soil temperature fluctuations, reducing heating in summer and cooling in winter. In addition, a major benefit of winter mulch is protection from repeated freezing and thawing of the soil. Newly planted, small or shallow-rooted plants are especially susceptible to injury or death due to upheaval from freeze-thaw cycles.

WA CES “The Garden Professors” Mulch: Just Do It

Other

Weed germination

Mulch reduces germination of resident weed seeds by preventing sunlight from reaching the soil. Weed seeds do germinate in mulch but seedlings are uprooted easily.

Soil-born disease

Mulch prevents splashing onto foliage and can reduce the incidence of fungal disease. Removal of fallen infected leaves is still required.

Plant injury

Mulch prevents fatal plant injury from mower & string trimmer wounds. While these wounds appear minor, disruption of plant cambium (inner bark) often leads to slow decline with death occurring several years after injury.