Mulch in the Desert: Gravel vs Wood Chips

In the desert southwest, gravel is often the default mulch used to cover yards. But there are also advocates for using wood chips instead. What are the drawbacks and benefits of each?

Have you ever wondered why desert landscapes are usually covered with gravel instead of wood chips or other organic mulches? Is it just a custom or matter of cost? Are there any benefits for plants or homeowners?

Let’s take a look at the benefits and drawbacks of both organic and inorganic mulches so you can decide which makes more sense for your situation.

What is Mulch?

Some purists say that gravel is not mulch, and that mulch has to be organic, but I disagree.

The US Department of Agricultural describes mulch as “a protective layer of a material that is spread on top of the soil.”

Mulches can either be organic (wood chips, compost, straw, pine needles, grass cuttings) or inorganic (gravel, decomposed granite, chat, and other size rocks). Both organic and inorganic mulches have benefits and drawbacks.

(To keep things simple, I’ll be using the terms gravel as a stand-in for inorganic mulches and wood chips for organic mulches throughout this article.)

Gravel: The Default Desert Mulch

Depending on where you live, there may be a custom of covering yards with gravel. Or you may live in a community that requires its use, at least in your front yard.

Benefits of Gravel

A layer of gravel on top of desert soil provides many useful functions and actually has some benefits over wood chips.

– Gravel keeps soil intact, preventing erosion from wind and rain. Unlike wood mulch, it doesn’t blow away with the wind and it doesn’t wash away when it rains.

– While some weeds still find their way between the rocks, gravel does help suppress weeds. It blocks light and keeps seeds from taking hold in soil.

– Gravel helps to retain moisture in the soil.

– Gravel doesn’t attract insects.

– Gravel holds heat, which can be a benefit in the winter, keeping plants warm and potentially reducing frost damage on some plants.

– Gravel rarely needs to be replenished, although it does need to be rearranged occasionally.

– If fire is a concern for you, gravel is fireproof.

– This last benefit is subjective. You may or may not love the look of gravel. I love the desert-aesthetics of rocks of all kinds — boulders, river rocks, and even gravel. Gravel harmonizes with our natural environment and reminds us that we’re in the desert. I love the desert and didn’t move here to pretend I’m somewhere else! 😍

Drawbacks of Gravel

– Gravel does not break down and improve the soil.

– A big drawback of gravel is that it holds heat longer than wood chips. You might expect that gravel would be measurably hotter than wood chips during the hottest part of the day, but surprisingly, that is not the case.

Using my infrared thermometer gun, I took the temperature of various surfaces in my yard — wood mulch, gravel, concrete, and bare dirt — in full sun on a summer day. All surfaces were within a few degrees of each other — around 160℉. 🥵 Mulch was actually a few degrees hotter than gravel, but it does not hold the heat as long.

– Gravel is an uncomfortable walking surface for people or pets. And if you happen to fall, it’s very unforgiving.

Skip Using Landscape Fabric

Another inorganic mulch option is landscape fabric, but it’s a particularly bad idea in the desert. It makes the ground hotter, leads to soil compaction, hinders the flow of oxygen and water in and out of the soil, and discourages the growth of beneficial microbes.

Wood Chips & Other Organic Mulches

If you’ve lived in other parts of the country, you’re probably familiar with the use of wood chips or other organic mulches as the default.

Benefits of Wood Chips

There are a few big benefits of using wood chip mulch.

– Wood chips hold moisture and, if deep enough, suppress weed growth.

– While wood chips get as hot as gravel, they cool off faster.

– As wood chips decompose, they add organic matter and nutrients to the soil, improving its quality over time. This is an important benefit, since desert soil contain less than 1% organic matter. This is especially important in a vegetable garden, but not so much for native landscape plants which are adapted to live in unimproved desert soil.

Drawbacks of Wood Chips

– As microorganisms break down wood chips, they consume nitrogen, making it less available to your plants. Since nitrogen is one of the most common nutrient deficiencies in desert gardens, this can be a concern.

– Wood chips may lower soil pH, making it more acidic. While this might be helpful for your citrus trees which prefer slightly acidic soil, it’s not helpful for most landscape plants which have evolved to thrive in alkaline soil.

– While wood chips will help hold in moisture once it reaches the soil, it can also form a barrier and prevent the water from light rains from reaching the soil.

– Desert plants like cactus, agave, and some wildflowers prefer to not be surrounded by organic mulch which can stay too wet, leading to rot.

– Wood chips float when it rains. During a gentle rain, they will rearrange themselves throughout your yard. After a gully washer, you may find much of your mulch has washed away.

– Wood chips may harbor insects. Some gardeners swear they do not attract insects, while others are convinced that they do. My go-to local garden center (Civano Nursery) surprisingly does not sell mulch because they believe it attracts insect such as termites, scorpions, and ants. My termite inspector advised me to never have wood chips near my house since it harbors termites.

– Wood chips not fireproof and can catch on fire. It’s a well-known phenomenon that wood chip piles build heat and can burst into flames. Alarmingly, even mulch that is spread more than a few inches deep can build up enough heat to spontaneously combust, especially in hot, dry weather.

Beware of Chip Drops

Some wood chips drops can contain unwelcome surprises. I’ve heard of chip drops that included trash, weed seeds, diseased wood, or insects.

If you get a chip drop of new wood or are thinking of using your own newly created wood chips, note that as microbes break down new wood, they use a lot of nitrogen and can generate enough heat to scorch your plants. Ideally, wood mulch should be seasoned before using.

Pro Tip!
Regardless of what type of mulch you use,
keep it at least 3″ away from plant stems or trunks.

My Experience with Wood Chips

One of my Tucson homes came with a small flower garden that abutted against the house. It was covered with wood chips, which caused me two headaches.

Every time it rained, the mulch floated away, making a mess of my pavers, patio, and gravel. And every year the house had termites in that spot, even after I removed the mulch. My termite inspector assured me their presence in that spot was not a coincidence.

Final Thoughts

While there’s a place for wood chips, I don’t think it’s the best choice for many landscape situations. If you live in a tract home in the burbs like I do, gravel is usually the only option.

If you’re goal is to improve your soil, consider top dressing with compost instead of using wood chips. Compost will add organic matter and nutrients to your soil faster.

But if you need a quick way to keep down dust, are looking for a soft walkway or place for your dogs or kids to play, or want to retain moisture in your vegetable bed, wood chips may be a good option for you.

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