Gravel vs. Mulch: Main Differences
Natural mulch is made from plants, such as shredded bark, wood chips, fallen leaves, grass clippings, straw, and similar biodegradable materials that will eventually decompose. In this article, we’ll focus on woody mulch products like shredded bark, pine bark nuggets, and wood chips, and skip grass clippings and pine needles. Bagged or bulk woody mulch is available in many colors, as well as undyed and natural-looking.
In landscaping terms, gravel, used here as a general term for simplicity reasons, is a mixture of sand and stone. It ranges considerably in size from large river stones, pebbles, and lava rocks to pea gravel and crushed granite. Gravel also varies in texture and color.
The Pros of Using Gravel Instead of Mulch
Gravel does shine for some applications. For example, the aesthetic of a river rock mulch in a rock garden can be stunning.
It is fireproof: If you live in areas where wildfires are a threat, rock groundcoverings provide a fireproof surface and defensible space around a home, under a deck, or to make a firebreak in the yard. But if they aren’t kept clean and free of leaves, conifer needles, and weeds, the visual appeal and usefulness as a fireproof material diminish.
Dry-climate gardening and rock gardens: In xeriscaping, when creating landscapes that require significantly less watering, rock gardens and dry swales are perfect spots for using gravel groundcoverings. Choosing rocks that complement the plants and perhaps larger boulders in a rock garden or xeriscape can add depth to the design and make it look more professional and natural.
Gravel doesn’t decompose: Over time, woody mulch will decompose. Gravel and rock products will still be there years later, although they may fade or lose their initial color. Gravel is much more permanent.
The Cons of Using Gravel Instead of Mulch
Gravel and rock products can be utilitarian or aesthetic, but they do come with some downsides.
Rocks and gravel trap soil carried by the wind: The sheltered crannies between rocks create a perfect spot for weed seeds to germinate and grow. Even with landscape fabric, weeds will still pop up and need to be removed. Removing larger weeds can be messy in a gravel mulch.
Frequent cleanup: A few leaves in a bark mulch bed don’t look out of place, but a layer of pine needles or leaves, or the grass blown out of the lawn mower, looks untidy in a gravel-covered bed. Pine needles, especially, can be difficult to remove, even with a leaf blower.
Excess heat: Gravel beds can heat up in the summer sun, creating a microclimate that may be too hot for many plants.
Escaped bits of rock: Gravel tends to wander out of the beds and into areas like your lawn, onto the sidewalk, or into the driveway. A few loose pieces of gravel can make a lot of racket in your lawnmower, and pose a danger when they become projectiles. For those with snowblowers, loose pieces of crushed gravel can spell trouble for the impeller. String trimmers will throw smaller pieces of gravel mulch, too. Woody mulch can also wash out of a bed, but a few wood chips don’t cause the same problems; they just fade away in the grass.
How to Choose: Deciding What’s Right for Your Yard
Both woody mulches and gravel are useful in the right situations. Beyond aesthetics and maintenance considerations, here are a few other factors to hlep you make the best choice for your needs.
Think about the future. Take a look at the exact location you intend to apply the rock or gravel. Consider utility needs like creating a firebreak, the possibility of changing plants or even the shape of the bed in the future (gravel is much harder to remove and plant through), and accessibility. Moving gravel is hard work.
Compare costs. Gravel is a one-time expense, but it can be significant. Don't be tempted to save money by skimping on the quantity of gravel you need. Often, homeowners and contractors lay down a weed-blocking fabric, and then use just enough rock product to cover it. Soon, soil particles and weed seeds blow in, and weeds are popping up everywhere.
Overcoming this issue requires using more rock, typically 3 to 4 inches, not just a thin layer for color and texture. The larger the gravel, the thicker the layer needs to be. Be aware of this when comparing costs. Wood-based mulches also require a 2- to 4-inch thick layer for effective weed suppression. While wood mulch is often less expensive to install, there will be a recurring cost to maintain it.
Consider your soil. If your gravel is limestone-based, it can slowly raise soil pH, which may be a problem for acid-loving plants like azaleas, rhododendrons, and blueberries. In those beds, stick with wood-based mulch instead. Woody mulch moderates soil temperature and encourages healthy soil microorganisms. Their decomposition supplies organic material in the soil, but that means wood-type mulches will need to be replaced about every other year, with an annual touch-up to maintain their effective thickness.
