Last summer, we released a roofwater calculator at Now, we’ve just unveiled our new “mulch estimator.” The former calculates the average annual precipitation that lands on your roof, road, parking lot, sidewalk, patio, garden bed, or field. The latter estimates how many yards of mulch you will need for your next mulching project. Imagine… all this without having to get off your butt to find the tape measure.

To use the new tool, just go to and click on “TOOLS” and then hit “NEW Mulch Estimator.” Enter your address, zoom in, and use your mouse to make polygons on your property. Each polygon describes an area, and instantly an estimate (based on a three-inch depth of mulch) appears at the bottom of your screen.

What’s the best mulching material for an arid land? Pre-Columbian New Mexicans survived here for centuries using river rock for mulch. These easily accessible cobbles are great for shading the soil and protecting seeds from winds, birds, and other forces of nature. Equally important is that rocks harvest water out of our thin, high-desert air. They soak up heat during the day and release it at night, and this convection process creates moisture. Remember the last time you picked up a stone from the earth? Most likely it was damp underneath.

All mulches have five basic functions. First, they retain moisture (mostly from precipitation events). Second, they protect soils and root zones from high winds. Third, they insulate the soil from extreme temperatures. Fourth, they reflect and absorb light. Fifth, mulches increase the nutrient value of soils by creating microbial habitat.

River-rock mulch, however, is not right for some modern sensibilities. Here’s a list of more-common mulches: straw, crusher fines, gravel, shredded bark, bark chips, pecan shells, compost, wood chips, and (free) shredded organic material from the transfer station.

My favorite mulch is straw. It comes in convenient packages. It’s light, and it slowly adds organic material to the soil. Straw is great at retaining moisture (as long as you don’t lay it down too thickly). It may look a little too bright and yellow at first, but give dead grass a little time in the sun, and it will turn brown like the color of the neighboring earth. Beneficial mycelium also thrive near straw, and there are few things better for your soil than mycelium.

Another great mulch is called “crusher fines,” which are tiny pieces of rock left over from the gravel-crushing process. They’re tan and look as natural as the mesa herself. Since the particles of crusher fines are heavier and drain better than hard-packed caliche, crusher fines also won’t erode nearly as much as our native soils. Both straw and crusher fines can be good weed barriers, too, but they’re not perfect at preventing all weeds, so beware.

Questions? Feel free to ask by finding me at my next public talk on the subject (at Untied Church of Christ on Sunday, March 17) or simply use my contact info below.

Nate Downey is the author of Harvest the Rain (Sunstone Press, 2010) and has been the “Permaculture in Practice” columnist in this magazine for 15 years. He’s been designing local landscapes since 1992 and can be reached at or 505-690-7939.

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