Coir is made from the coconut fruit, which is technically a kind of drupe, as is the more commonly known peach. A peach has a pit (the seed), surrounded by a sweet fleshy mesocarp (the part you eat). The coconut fruit has a seed (the coconut), surrounded by a fibrous mesocarp which was once considered to be a waste product when collecting coconut. This component is now reserved for the fiber (and to make coir). Some other common drupes include olives, apricots, cherries, plums, and coffee.
To prepare coir, the coconut fruit is split open and the coconut seed removed (to be used as a “coconut”), and the husks are collected. The husks are soaked in water (salt or fresh) for an extended time, usually months, to encourage the pulp in the husk to decompose. This makes it easier to separate skin, coco fibers and pith in a process known as retting. The coir is then rinsed to help remove debris and salt remaining after the retting process.
Coir, intended for use as a growth medium, may be sold loose in bags, compressed into blocks and other shapes or used as an ingredient in potting mixes. The fiber contributes to aeration, and the ratio of fiber to pith in coir varies by application and source. Using both pith and fiber together produces a lighter final product with better aeration than using pith alone which may lead to compacting issues over time.
One benefit of using coir, is that the base material (coconut fruit) is both organic material from a plant, and from a resource that is perennially harvestable. Since it isn’t the parent plant that is used, but rather the non-destructive collection of the fruit from the plant, coir resources used one year can be replenished the following year without damage to the parent plant.
Coir holds up well to prolonged exposure to moisture, and does not become hydrophobic when dry. It can be used as part of a hydroponic gardening system, a component in a potting mix, or as a soil amendment.
Coir, naturally, has a pretty good Cation Exchange Capacity (CEC) but many of the cation sites will already have sodium (Na) or potassium (K) present. Treating the coir with a solution of calcium (Ca) and optionally magnesium (Mg) reduces the amount of sodium and potassium by replacement in a process known as buffering. High quality coir is usually both washed and buffered before packaging. As an alternative to buffering; increasing the amount of calcium and magnesium in the chosen nutrient solution will eventually have the same effect albeit at a slower rate of replacement.
As coir has a natural pH of 5.7- 6.5 it does not require liming before use. Proper adjustment of the nutrient solution should be all that is required. It also has very little in the way of nutritional value (other than the potassium), which minimizes conflicts with existing feeding schedules. It holds water well, but is not prone to overwatering.
Coir’s natural characteristics make it a popular growing medium that is well suited for use in a variety of garden and greenhouse applications.