One of the benefits of belonging to plant societies is receiving their informative journals. The December 2012 journal published by the Cyclamen Society (cyclamen.org) in Great Britain has an article entitled, “A Decent Peat-Free Compost,” by the society’s treasurer, Keith Fry. Many gardeners are eager to learn more about using coir as a substitute for peat moss, so I’ll share some of his information.
According to Fry, harvesting peat moss from bog deposits endangers the plants and animals that rely on bog habitats, and bogs are virtually non-renewable. (For an update on the status of peat bogs in Canada, see “Give Peat a Chance” in Garden Making # 11, Fall 2012.) Substituting coir for peat moss is a viable solution, he writes.
Coir is a layer of plant fibre contained in the husk of coconuts, and has similar properties to peat moss. It’s also renewable and appropriate for garden use. “The coconut is botanically analogous to a plum, but instead of fleshy material enclosing the hard-shelled seed, the outer material, called coir, is the waste product of coconut cultivation,” Fry writes. Commercial coconuts for export are an important crop in India and Sri Lanka, and some people claim the economies of both countries would benefit from an increase in demand for horticultural coir.
I have a one-litre block of coarse-grade compressed coir on the shelf in my basement (purchased for repotting orchids), where it has been waiting for me to become enlightened on how to use it. When soaked in a bucket of hot water, the compressed block will expand to about six or seven litres of material. Coir is also available loose, as a fine-milled grade, packaged in 35-litre bags for garden use (look for that in garden centres next spring).
Coir ranges between 5.5 to 6.5 pH, not quite as acidic as peat moss, but still a good product for planting rhododendrons and roses. These both appreciate generous amounts of organic material around their roots. Coir also compares well with the water retention capability of peat moss, and improves drainage and oxygen retention.
Fortunately, Fry gives his recipe for substituting coir in his own planting mix, as follows: five litres of reconstituted coir, five litres of recycled green waste (such as leaf mulch or homemade garden compost), 25 grams of pelleted slow-release fertilizer, and 0.5 litre of perlite or coarse grit. This would make an excellent potting soil, and could be prepared in larger quantities to use in planting holes. Thanks, Keith Fry, for sharing your recipe.