The Mulch Debate: Organic vs. Inorganic

26 November 2019
 Categories: , Blog


When it comes to mulching your flower beds and landscape plantings, you have two choices -- an organic or an inorganic mulch. Organic mulches for ornamental beds are typically made from bark, wood chips, or pine straw. Inorganic mulches most often consist of pebble or rock mulches, but rubber mulches are also an option. This guide can help you pick the best one for your garden.

Soil Moisture

Moisture retention is touted as one of the major benefits of mulching. When it comes to this ability, organic mulches tend to excel. Rocks can absorb heat from the sun, which may actually cause them to heat the soil, so there is more evaporative moisture loss. So, with the exception of mulching desert plants that prefer drier soils, organic mulches are typically the better option if moisture loss is a concern.

Weed Suppression

Both organic and inorganic mulches can suppress weeds. For organic mulches, you need at least a 3-inch deep layer of mulch for weed suppression, and any small weeds that do survive must be hand-pulled. Inorganic mulches are typically installed over weed-blocking fabrics to ensure that no weeds make their way into the mulch since it is much more difficult to pull weeds from rocks.


Some plants thrive in drier soils and can't survive if the root zone stays moist. This is the one time that inorganic rock mulches tend to out-perform organic mulches. Rock mulch does not hold moisture in its layers, so soils tend to drain and dry more quickly.

Soil Insulation

Soil temperature fluctuations, particularly in winter, can have major effects on plant roots. Both organic and inorganic mulches provide insulation to maintain a more steady temperature, with organic options out-performing rocks and other inorganic mulches. Rocks can heat up in the sun, which adds warmth in winter but can cause heat damage in summer, so they should only be used with heat-loving plants.

Nutrient Benefits

Only organic mulches supply nutrients to the soil and plants. As organic mulches decompose each year, you can turn them into the soil to provide nutrients before applying fresh mulch. Inorganic mulches should never be incorporated into the soil -- in fact, a layer of fabric is typically placed beneath inorganic mulches so that they can't work their way into the soil. This fabric layer is especially important if you are using a man-made mulch, like rubber.

For more help, contact a residential mulch company.