Gravel and wood mulch can cover the same square foot of bed and look, superficially, like interchangeable choices. Underneath, they do almost opposite things to the soil. Anyone weighing gravel vs mulch landscaping should understand those differences before committing, because the ground cover you spread changes soil life, moisture, and root-zone temperature for years.
Organic mulch feeds the soil; gravel does not
The defining difference is decomposition. Wood chips, bark, shredded leaves, and other organic mulches break down over time, and as they do they add organic matter to the soil, feed soil organisms, and improve structure. Colorado State University Extension notes that organic mulches conserve soil moisture, moderate soil temperature, suppress weeds, and improve the soil as they decompose. Gravel does none of this. It is inert, so it never enriches the soil, and because it does not break down it never needs replenishing the way mulch does. That permanence is gravel’s main selling point and its main limitation: low maintenance, but zero benefit to soil biology.
Soil temperature under gravel versus wood
The two materials handle summer heat very differently. Organic mulch insulates and keeps root zones cooler and more even. Stone, by contrast, absorbs and radiates heat; a gravel bed in full sun can drive soil temperatures up and stress the roots beneath it, and it reflects heat onto nearby plants. The moderating effect of organic mulch on soil temperature is one of its documented benefits, and it is a real advantage in hot climates and around shallow-rooted plants. Reserve gravel for spots where heat loading is not a concern, such as pathways, xeric plantings adapted to hot ground, and drainage areas.
Depth and the volcano mulching mistake
More mulch is not better. The right depth for organic mulch is generally about two to four inches; piled deeper, it can stay soggy, shed water, and suffocate roots. The most damaging error is the so-called mulch volcano, where mulch is heaped up against a tree trunk. Penn State Extension guidance on mulching landscape trees explains that mulch should be kept a few inches away from the trunk, not piled against the bark, because mulch against the trunk holds moisture that promotes rot, disease, and pest problems and can girdle the tree. Spread mulch in a flat, wide ring with a clear gap around the trunk flare, shaped like a doughnut and never a cone.
Landscape fabric usually fails
Landscape fabric is sold as a permanent weed solution and rarely delivers. Within a few years, dust, decomposed mulch, and organic debris accumulate on top of the fabric and form a thin soil layer where weeds happily root, so weeds grow above the barrier while the fabric blocks desirable plants and worms below it. It also impedes the natural incorporation of organic matter into the soil. For most beds, a good layer of mulch renewed periodically suppresses weeds more effectively and keeps the soil healthy in the process.
Rubber and dyed mulch, questions worth asking
Not every product marketed as mulch behaves like traditional wood chips. Penn State’s survey of available mulch options runs through the range of materials, from wood and bark to stone and manufactured products, and their respective tradeoffs. Rubber mulch does not decompose and so adds nothing to the soil, and questions persist about what it may leach and how it behaves in heat and fire. Dyed wood mulches are often made from recycled wood of uncertain origin, and while the colorants used are generally described as landscape-safe, it is reasonable to ask what the underlying wood was. When soil health is the goal, undyed natural wood or bark mulch remains the straightforward choice.
