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.

| Spring 2017

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.

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