There is much talk about what soil conditioner your garden needs best: Sphagnum peat mouse or coconut coir? The debate is about sustainability. Another is efficiency.
The truth is that both are beautiful gardens. They are both natural and herbal. Both contributed to heavy clay soils and improved the retention of water in sandy soils. Each one has a list of nutrients it provides to the soil in its own right. Both promote beneficial natural populations of microbials.
Both have inconveniences, too. And here comes the debate, both the minor disadvantages that can be offset and the bigger ones that can’t be offset.
Coir is the relative newcomer to the garden in its different forms. Lang popular with hydroponic gardeners, it takes these good things into the garden, where it acts like the sphagnum mouse because of its water retention, a deterrent from fungal gnats and some illnesses, and its root support structure.
Indoor coir farmers have long been repurposed into vegetable gardens and compost stacks for their discarded hydroponic coir. Outside as well as in.
Both coir and sphagnum turkey soak up much water. Coir keeps water more than perlite and rock wool in the long term, suggesting keeping water longer in the garden. Both air trappings are fantastic in soil, air that benefits the roots of the plants.
Usually, the pH of coir is 6-6,7, nearly neutral. The addition of coir will retain the pH of the soil you add. Sphagnum is often acidic in potting ornamentals that love acids. There may have to be minor changes. Of course, Sphagnum only forms part of a comprehensive mix of soils, seldom up to a third of what is indicated in the formula Square Foot Gardening Mel Bartholomew, making it not so difficult to adapt modest pH increments.
In salts, coir may be high. It often collects extra salts after harvest, cultivated in saltwater conditions. Some farmers advocate washing even pre-sprinkled brands to remove salts. In addition to washing certain brands, they are composted to create a more balanced mineral supply.
The high potassium content of coir has been observed to interfere with the absorption of calcium. Again, this issue may be addressed in garden soils by the use of calcium supplements.
A Utah State Study (link not live anymore) showed “poor plant growth in coir,” which was contradictory to the success of all types of indoor growers employing coir in hydroponic conditions (oiliness, just peat or coir both coupled with perlite for drainage and nutrient solution). “No coir brand has consistently performed better than peat sphagnum,” it finds.
While we propose a little care before being used and some addition to enhancing the calcium, we do not believe that the variations between peat and coir that have been found, as recommended in the research, are “quite cautious.” There appears to be tremendous caution here without modification or additional provisions.