Sustainable Eats

Photo courtesy of Shacker on Flickr.

I’ve been on the hunt for the perfect mulch lately because it’s hard to tell with this never-ending soggy weather but we are predicted to have a drought this summer.

I’m doing my part by re-routing the zones on my irrigation system so that I can use low pressure T-tape to water the beds and I’m placing my repurposed cofee bag containers under young fruit trees to act as slow water release and mulch. I have the vegetable beds densely planted so there is minimal exposed soil. But I still have some perimeter areas with full sun exposure on a gradual slope. They dry out quickly.

The coffee beans I used around the berry bushes are a beautiful mulch – both visually and stunningly effective at keeping the soil underneath them evenly moist. When the sun shines down on them they proffer up an enticing aroma and are doing an amazing job of correcting my soil formerly known as lawn to get the pH right for berries. I just don’t have enough of them.

In a previous garden I had hazelnut shells in the walkways which were also beautiful to look at and did a great job of weed control. When I contacted Holmquist Hazelnuts, though, they told me the shells they sell are not organic so that rules them out.

I contacted Theo Chocolates and found out that they sell their cocoa mulch but after talking to some master gardeners I found out that there is always a possibility of cocoa remaining in the mulch which can be lethal to wandering dogs. And the fact that I’ve considered rolling in the coffee beans to pick up their scent leads me to believe the same thing may happen with dogs in my cocoa mulch. So that rules out that one.

Lucky for me I have a good friend who is a master composter so I asked him for suggestions. He and his wife Emily are the dynamic duo behind Seattle’s very own green Moment Architecture.  This is what he had to say. Please check out his link at the bottom to read his complete podcast on Seattle Tilth’s site.

Mulching with Joshua

As the summer heats up, the sun tends to dry out the soil in your garden. In order to keep soil moist enough to sustain your plants, you may want to consider using a mulch.

What is a mulch?

A mulch is something you put on top of the soil, rather than something you incorporate into the soil. Things that you put IN the soil should be fully composted, as the composting process temporarily ties up nutrients required for plant growth. However, with mulches, you have the option of using uncomposted or partially composted materials, as any temporary nutrient deficiencies created as the mulch decomposes are likely to occur above the root zone.

Mulches degrade over time into organic matter that enriches your garden soil. You should add organic matter to your soil every year, in addition to organic fertilizers which provide nutrients removed from garden soil when you harvest your garden plants. Organic matter helps your soil retain moisture and sustains a population of important micro-organisms that maintain symbiotic relationships with your garden plants. Organic matter has many other functions too numerous to list here.

What mulch should I use?

If you’re talking about perennial beds full of woody plants, use a woody mulch such as arborist chips. They’re free, though you have to call around and coerce them to dump in your driveway. I keep them coming back by always giving 4 microbrews to the arborist crew that delivers the chips.

My favorite mulches for vegetable gardens include Chicken’n'chips, Beauti-gro, and Steerco. All these combine byproducts of the lumber industry and manure from animals. Their particle sizes are more varied than Cedar Grove compost, so they remain porous and open to water. All affordable mulches make use of some waste stream or other.

Cedar Grove Compost uses Seattle’s curbside-collected yard-waste wastestream. All that waste goes to a big facility in Woodinville, where it’s composted at high temperatures that kill all weed seeds and pathogens (and soil life). It’s all certified organic. It’s excellent for incorporating in the soil, but it’s not a perfect mulch because its particles are so uniform they tend to compact under the pressure of a hose or heavy rain. I like to mix cedar grove with chopped straw or freshly mown grass to try to open up its structure a little bit. In this mixed form, it’s a fantastic mulch and the only organic mulch you can find. Another option is to apply the CG compost slightly wet, so it forms chunks with particles about the shape and size of course granola. If allowed to dry after application, these chunks maintain a kind of openness that allows moisture to penetrate the mulch.

Straw is a heavily used mulch around here, but it has lots of seeds and looks rather backwoods in small beds, where it tends to stick out all over the place. I like to use straw in flat, open gardens where the weeding is easy.

One easy mulching technique is just to use mown grass, collected from the neighbors. I have trained my neighbor to dump his mown grass in my vegetable garden’s paths. The next day, I spread it around to create a thin layer around the bases of my vegetables. Although the thin layer of grass quickly browns, it’s enough to shade the soil, feed the worms, and even reflect additional light up to my garden plants. Grass does tend to compact when sprayed with water. It CAN shed water, if spread too thickly. One way to loosen grass and make an even better mulch is to toss it with cedar grove compost, coffee chaff, chopped straw (chopped for aesthetics) or coffee grounds. Again, the more varied particle size of this combined mulch is better than any of the ingredients individually.

Perhaps the simplest mulch of all is a dust mulch. NW garden guru Steve Solomon recommends this mulch, as he is very concerned with the way degrading mulches temporariliy tie up nutrients. A dust mulch is created simply by hoeing. Hoeing breaks the “capillary action” between the soil’s surface and the soil below. Capillary action is a fancy name for the physics by which soil moisture below the surface is drawn up to replenish dry surface soil, where it then evaporates, drawing even more moisture from below. Hoeing also helps by reducing weeds. More soil moisture is lost through use by weeds than is lost through direct evaporation by the sun.

Solomon’s method is a little far out there for me. When I lift up my vegetable garden’s layer of grass mulch, I see worms going crazy with joy. Their increased activity create little vertical tunnels for water to better reach plant roots. Their digestion helps stabilize soil nutrients so they won’t wash away in the rain.

Perhaps the best mulch of all is home compost. Unlike compost from an industrial facility, it’s chunky as heck and full of life. However, even the largest yard cannot generate enough compost to dig in to the garden, much less use as a mulch where some of its microfauna will be killed in the deadly zone on top of the earth.

I use different mulches in different beds, depending on what’s available, how I want that bed to look, and the kinds of plants I’m growing there. It’s good to mix things up a bit over the years, since different mulches provide different kinds of nutrients. As with eating, a wider variety will expose us to a wider variety of micronutrients.

Finally, mulches should be kept away from the bases of your garden plants. A thick mulch against the base of your favorite fruit tree can rot the trunk.

If you want to learn more about mulches you can listen to a podcast episode on mulches I created as part of Seattle Tilth’s Master Composter training. program.

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