Going peat-free

 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.

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. 

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.

 

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.

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?

Sustainable-enough potting mix

To test the usefulness of my homemade potting mix and compare it to commercial products, I’ve been working this winter on propagating African violets. I made the potting mix to avoid using peat, which I learned is not a renewable resource. The mix is half compost from my yard and half coir, or coconut fiber.

    Like so many of my gardening methods, it’s “sustainable-enough” rather than ideal. That’s because the coir comes from Hawaii, accruing significant carbon cost on its 6,000-mile journey to Massachusetts. On the plus side, coir is a byproduct that I can put to good use, and compared to depleting peat bogs, which are major carbon sinks, I think non-local coir is the better alternative.

    I’ve had luck with African violets as houseplants probably because they tolerate neglect. My collection has been living for years on pebble trays next to an east-facing window. Their winter blooms are a morale booster. I’ll betray my amateurism by admitting that I haven’t kept track of the names of the varieties I’m growing. My favorite has blue flowers and purplish foliage. 

The pink ones are nice too.

    I wanted to try multiplying my collection by rooting single leaves. I cut off a few with stems about two inches long and stuck them into moistened potting mix in November. I enclosed them in plastic bags for a humid environment and put them under a grow light in the kitchen. Nothing happened for many months.

    Meanwhile, I discovered an excellent youtube video demonstrating how to propagate African violets from leaves, made by an anonymous benefactor who obviously knows what she’s doing. After watching her demonstration, I was able to start a new batch with several improvements in my technique.

    First, since the new sprouts grow from the cut end of the stem, I cut the stems shorter. I used smaller pots and didn’t tamp down the potting mix. I learned to cut the stems at a slant for more surface area and to cut the leaves in half to encourage them to put their energy into reproduction rather than photosynthesis and leaf enlargement. 

    This week I noticed some little leaves growing up at the base of the old ones in both batches. 

I took the pots out of their plastic bags and gingerly dug out the mother leaves. Voila! There were little plantlets growing from the cut ends. The new leaves were no more than a quarter inch long, some much smaller, but they had their own roots. 

 

    I pulled the babies away from the mother plant, doing my best not to break them. I planted the best ones in a recycled six-pack from last year’s garden center annuals, 

encased them in another plastic bag, and replaced them under the grow light. With luck, I’ll have reasonable-sized plants to enjoy or share next winter.

    The non-peat potting mix did its job just as well as the peat-based mix I used to use. Score one for sustainability.