Kicking the peat habit

Mom, apple pie and peat moss? If you thought, as I used to, that peat moss is a renewable natural product, I’ve got some bad news for you. It’s time to break with peat-based potting soil.

            Peat moss was part of my gardening life from early on. It was the main ingredient of every growing medium I bought. But it turns out that we’re using it up, and contributing to climate change in the process. It wasn’t until I read Sarah Reichard’s book The Conscientious Gardener that I learned the sad truth.

            The problem with harvesting peat is that it's created so slowly. Peat comes from wetland plants—sphagnum moss but also sedges, grasses and reeds-- decomposing very slowly in oxygen-poor water. In peat bogs, peat forms at less than a millimeter per year; the peat we garden with took thousands of years to form. It’s hard to imagine sustainable harvesting given that rate of growth. 

Sphagnum moss growing at Eagle Hill Bog, Campobello Island, New Brunswick

Peat sequesters one third of the world’s soil carbon, more than all the trees in the world. When the peat is harvested, the carbon is released and the carbon sink it provides is eliminated.

            Swarthmore College, whose campus includes Scott Arboretum, has stopped using peat-based potting soil and switched to a mix of coir, or coconut fibers, worm castings, mushroom compost, and rice hulls. Eventually peat-free potting soil will be widely available in the US. In Britain it's already mainstream.  
            Until we catch up, I decided to make my own peat-free mix, using a basic combination of one part coir to one part screened compost from my own yard. A local hydroponic gardening shop provided bagged coir. A by-product of coconut husk processing, coir is the pith left over after separating out longer fibers for use as bristles, filaments, mats, padding, and biodegradable textiles.

            Right away I could see why this material would make a plausible substitute for peat. It’s almost the same color and consistency, a little redder and coarser. Combining coir and compost yielded a handsome, fluffy rich brown mix that already looked absorbent. I used it to pot up annuals, cannas, and elephant ears. One thing was immediately evident: my potting mix was not sterile or weed-free. My compost hadn’t heated up enough to kill weed seeds. In every pot, sprouts began to surface, but the weeds were easy to pull out.   

            By the end of the growing season, I was convinced that my containers had done just as well using the coir and compost mix as they had in previous years with commercial potting soils. I don’t miss peat, because the new mix seems to work fine.