Why Not Give Organic Mulches a Try?
It seems that there are as many landscapes featuring aggregate as there were 20 years ago. Gravel continues to proliferate through our landscapes, despite the overwhelming evidence that graveled landscapes slowly kill trees and increase home cooling costs. There are alternatives to the gravel landscape and I hope that this post will ease the concerns people have about exploring them.
When people realized that water was a limited resource in New Mexico and started ripping out lawns, they correctly determined that the ground needed to be covered with something to keep the wind and rain from eroding the exposed soil. Enter mulch. According to the Merriam Webster Dictionary, mulch is defined as a “protective covering spread on the ground to reduce evaporation, maintain even soil temperature, prevent erosion, control weeds, enrich the soil, or keep fruit (such as strawberries) clean.” Notice the enrich the soil part (emphasis added by the author). It takes geologic time for gravel to enrich the soil, so why is gravel known as the standard for mulching in New Mexican landscapes? The answer is driven by maintenance and has been bolstered by an array of myths about organic mulches.
Organic mulches are those derived from sources that were once alive, such as bark mulch, wood mulch and pecan shell mulch. Unlike gravel mulches, organic mulches replenish organic content in the soil as they decompose. This not only enriches the soil with nutrients, it also improves the moisture retention capacity of the soil – an important attribute in our arid climate. Moreover, organic mulches are lighter, which prevents root damage caused by soil compaction. And perhaps most significantly for your comfort and your air conditioning bill, organic mulches keep the ground cooler, which reduces ambient air temperature.
These are the reasons I most frequently hear for why people use gravel mulch in their landscapes instead of organic mulches, followed by the reasons why I believe they are wrong. Read them and be a confident leader in setting a better standard for landscape design in your neighborhood.
1. “That’s how you zeroscape. Cactus and gravel.”
First of all, the correct term is “xeriscape” not “zeroscape”. According to the Xeriscape Council of New Mexico, the word xeriscape is derived from xeros, a Greek word that means “dry.” Xeriscape refers to a landscape that uses little supplemental water. A well-designed xeriscape can be a lush oasis if properly installed and maintained. There is no rule requiring the use of gravel in a xeriscape. In fact, organic mulches enable your landscape to be more water wise. Each 1% increase in soil organic matter helps soil hold 20,000 gallons more water per acre.
2. “Wood mulches rob the soil of nitrogen”
This is only true if you mix the mulch into the soil instead of laying it on top of the soil. The reasoning is that undecomposed woody material is a carbon source for soil microorganisms. They become very excited about the food that has suddenly become available and start reproducing at a rapid rate. Microbial reproduction requires nitrogen to build their bodies, and that is why nitrogen becomes unavailable to plants– the microorganisms are using it all to multiply. Since decomposition only occurs on the surface area of the carbon source, the soil that the root zone occupies is left unaffected.
3. “Wood mulch blows away”
There are many wood mulch options that stay in place quite well. Mulches that vary in particle shape and size tend to lock together better and resist movement more than those that are lightweight and chipped to a uniform particle shape. Look for a mulch with rough edges. Another factor is design. I recommend that, whenever possible, to design planting areas below the grade of pathways and other impervious surfaces. This configuration captures water and harnesses wind power to collect leaf litter where it can decompose and support the soil ecosystem. Side benefit? Mulch stays in place. On a final note, pecan shell mulch often gets a bad rap for blowing around, which is unfortunate since pecan shells are an excellent choice for mulching. We have many die-hard pecan shell mulch customers who swear by its staying power so long as it is wetted and rolled during installation.
4. “Gravel is easier to maintain”
If that was true, why do you see so many piles of dirty, weed infested gravel sitting on people’s driveways waiting to be hauled off? Those who have worked with gravel know that it is no fun to shovel in, and even less fun to shovel out of a landscape. The use of gravel was promoted by a maintenance strategy based on going out twice a year to spray the ground with pre-emergent herbicides, many of which are deadly to bees. I promote a different approach. Organic mulches improve soil health, making your plants easier to maintain. Applied at a depth of 3”, mulches will suppress the germination of seeds. However, the wind in New Mexico will always blow in dirt and weed seeds, and those seeds will grow on top of gravel and in the cracks of asphalt parking lots just as readily as on organic mulch. The bottom line is that there is no such thing as a maintenance free landscape. There are easier to maintain landscapes, and those mulched with organics fall into this category – given the right tool and the right attitude. A scuffle hoe or a Skidger™ is easy on the back and smears out weeds as they first emerge. If those weeds are caught at the right time, they’ll simply dry up and disappear back into your soil.
5. “If you put woody mulch down, you’re going to attract insects and rodents.”
Organic mulches will not attract new populations of pests into your landscape. If you already have a cockroach problem, you’ll still have a cockroach problem. One of the worst cockroach hiding places I have found was underneath rubber ski-flooring material applied over a concrete pad where the water had nowhere to go. Think dark, dank, and inhospitable – not the environment created by organic mulches. As for termites, their colonies live in the soil and require high moisture levels to prevent desiccation. A three-inch layer of coarse organic mulch cannot sustain the constant level of moisture necessary for their survival – particularly in our climate. (source: http://web.extension.illinois.edu/state/newsdetail.cfm?NewsID=15506). Nonetheless, it is good practice to leave some space between mulch and the house foundation. After hundreds of customers and over 20 years, the only issue that has been reported to us regarding organic mulches has been that the birds like to pick out remaining bits of pecans in the pecan shell mulch. Customers enjoy the visit from local winged wildlife for about two weeks, then they’re gone.
6. “If you use woody mulches you’ll make the soil too healthy and you’ll end up growing more weeds”
Remember that the goal in your garden is healthy soil and happy plants. It makes little sense to deprive trees, shrubs, flowers, native grasses, pollinators, and birds of life because of fear of weeds. Weeds are the scabs of the earth and flourish where the Earth is exposed and the soil needs healing. Many weeds have evolved to mine the soil for nutrients and bring them up to where they can be used by other plants. Their tenacious roots work hard to break up compacted soil, and when they rot in place after a season they contribute organic matter back to the soil. If you care for the Earth, the Earth will not require so many weeds. Other weeds are friends, like the dandelion which was brought over by European colonizers who valued them for medicinal purposes. Weeds are also friends to pollinators, offering some of the first forage for bees in the early spring.