I was encouraged to see a recent New York Times story about replacing peat-based potting mix with more sustainable materials. I just wish the writer, Margaret Roach, had gone farther and described her experience with the new materials.
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| Mer Bleue peat bog in Canada |
Peat has been the dominant ingredient in growing media for a long time because it’s great at absorbing water and nutrients but lets air and water flow through, and it’s slow to decompose. The problem is that peat is not a renewable material, at least on a human time scale. Peat bogs are giant carbon sinks, sequestering more carbon than all the trees in the world. Extracting peat from peat bogs releases carbon dioxide into the atmosphere, contributing to climate change.
Peat forms very slowly when wetland plants decompose in oxygen-poor water. The peat we garden with took thousands of years to form. As we confront the climate emergency, we need materials for growing plants in containers that come without environmental degradation and a high carbon cost.
When I learned about peat’s downside, I switched to making my own potting mix by combining sifted homemade compost with coir, or coconut fiber. This mix works just as well for my container plants as the peat-based potting mix I used to buy at the garden center.
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| I combine coir and compost to make peat-free potting mix |
To make the volume of potting mix I need, I buy 5-kg compressed bricks of coir from a hydroponic growing outlet or Home Depot. You can also buy big bags of loose coir, but whatever kind you buy, it needs to have been washed to remove salts. To use it, just wet it by soaking in a barrel. Sounds like an easy solution, right? Unfortunately, coir comes with a carbon cost for shipping it here from tropical areas.
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| Container plants flourish in the peat-free mix |
From Ms. Roach’s article, I learned that US researchers are working on developing wood-based recipes for potting mix. Ideally, those could be made from local materials. She interviewed Brian Jackson, a professor at North Carolina State University and director of the Horticultural Substrates Laboratory. This is another area where Europe is way ahead of us. They’ve had wood-based growing media on the market for 30 years. Britain is moving toward banning peat in horticultural products.
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| An example of UK peat-free compost made from bark and wood |
Jackson’s team reports best results from a combination of peat and wood. Combining them creates a stable, spongy material that retains water especially well. It’s porous and provides lots of air space, creating an excellent environment for root growth. I’d rather drop the peat from the recipe completely. How about wood fiber combined with compost? That seems to be working in Europe.
So far, wood fiber for growing plants seems to be available to large-scale growers in the US but not to home gardeners yet. While we wait, I recommend the coir-compost blend. But the best thing we can do as consumers is to ask garden centers to stock peat-free potting mix, whether it's based on coir or wood fiber. Why should Europeans get all the good stuff?
