Coir in the Garden

Try using coir — the pith from coconut processing that’s more sustainable than peat moss and just as effective as a growing medium.

Wetland

Peat forms from wetland plants in oxygen-poor, water-saturated environments.

Photo by Fotolia/aloisphoto

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Today, many of us home gardeners are taking a closer look at the way we garden, aiming to upgrade to more sustainable practices and bring our passion for gardening in line with our environmental principles. Leaving peat moss out of our gardens is one meaningful step we can take toward combating climate change.

If you grew up gardening in the last century, you probably cherish peat moss as the next best thing to Mom’s apple pie. When my dad taught me to garden, he showed me how to dig bales of peat moss into vegetable beds to improve the soil’s ability to hold air, water, and nutrients. Peat was the main ingredient in every growing medium I bought. I never stopped to ask where my peat moss was coming from. I thought of it as a naturally good thing, like adding cow manure or compost to my soil. Then, I learned that peat isn’t a renewable or sustainable product — at least on a human timescale. I decided it was time to kick my peat moss habit.

Peat forms from wetland plants (such as sphagnum moss, sedges, grasses, and reeds) that decompose very slowly in oxygen-poor, water-saturated environments. In peat bogs, peat accumulates at less than one millimeter per year — a slow enough rate that it’s considered a nonrenewable resource. The peat we use in our gardens took thousands of years to form. And while peatlands cover only about 3 percent of the Earth’s landmass, they sequester about one-third of the planet’s soil carbon — more than all the forests in the world combined.

In Great Britain, the Royal Horticultural Society and many other prestigious gardening organizations use and advocate peat substitutes, such as coir (the pith left over from coconut processing). An early American adopter includes Swarthmore College, which stopped using peat-based potting soil in its Scott Arboretum in 2007 and switched to a locally-produced mix of coir, worm castings, mushroom compost, and rice hulls.

Sustainable Options

It’s true that peat makes an excellent growing medium. An ideal potting mix is dense enough to retain water and nutrients while keeping plants from tipping over, but it also allows water and air to flow through easily. In commercial mixes, peat has these qualities, in addition to decomposing slowly. It’s not the only option, though. Coir, composted bark, and byproducts of food processing prove to be equally effective media for growing plants commercially and in home gardens.

Coir, for example, has almost the same color and consistency as peat moss, and blending it with compost yields a rich, brown, highly absorbent potting medium. In fact, coir holds water even better than peat and decomposes more slowly. I find that my summer container plants do just as well with the coir-and-compost mix as they did previously with peat-based potting soils.

You have the best chance of finding coir at home improvement stores, garden centers, or hydroponic growing outlets. It’s sold loose or in pressed bricks, not unlike small bales of peat moss. A coir brick is easy to hydrate by soaking it in water inside a large trash barrel or other container. Whatever form of coir you use, you’ll want to ensure that it comes from a reputable source and has been washed to remove salt because low-end coir is sometimes processed in sea water. If you object to the carbon cost of coir shipped from coconut-growing areas, you can seek out more local materials, such as leaf mold, rotted sawdust, or composted bark or wood chips. When we give up peat completely, we’re going to find even more innovative and economically viable uses for lots of materials that have heretofore been disposed of as waste.

By reducing your use of peat for gardening, you’ll be helping to slow climate change and protect a unique and important habitat. Try making your own peat-free potting mix at home, or ask your garden center to stock peat-free products. The market will respond, and we can rest easy knowing we did our part to spare the peat bogs and the planet.


DIY Coir Potting Mix

You might be able to find peat-free potting mix at garden centers or home improvement stores. If you can’t buy it, you can make your own mix at home by combining one part coir with one part screened compost. The coir would otherwise be disposed of as waste if not used for growing medium, so you can feel good about putting it to use.


Rebecca Warner is a home gardener in Newton, Massachusetts, who has worked toward a sustainable ornamental garden for 30 years. Her book, The Sustainable-Enough Garden, is the story of her quest to make a beautiful garden that’s environmentally friendly. She maintains a weekly garden blog at The Sustainable-Enough Garden.