Sphagnum peat and coir have nearly identical water retention curves. They both retain about 90-95% of their volume in water at saturation and release it over approximately the same curve until they both lock water up so tightly it's unavailable for plant uptake at about 30-33% saturation. Coir actually has less loft than sphagnum peat, and therefore, less aeration. Because of this propensity, coir should be used in mixes at lower %s than peat. Because of the tendency to compact, in the greenhouse industry coir is primarily used in containers in sub-irrigation (bottom-watering) situations. Many sources produce coir that is very high in soluble salts, so this can also be an issue.

Using coir as the primary component of soils virtually eliminates the reasonable use of lime or dolomitic lime as a Ca source because of coir's high pH (6+). Gypsum should be used as a Ca source, which will also help eliminate problems associated with coir's low S content. All coir products are very high in K, very low in Ca, and have a potentially high Mn content, which can cause antagonistic deficiencies and interfere with the uptake of Fe.

I haven't tested coir, but I have done some testing of CHCs (coconut husk chips) with some loose controls in place. After very thoroughly leaching and rinsing the chips, I made a 5:1:1 soil of pine bark:peat:perlite (which I know to be very productive) and a 5:1:1 mix of CHCs:peat:perlite. I planted 6 cuttings of snapdragon and 6 cuttings of Coleus (each from the same plant to help reduce genetic influences) in containers (same size/shape) of the different soils. I added dolomitic lime to the bark soil and gypsum to the CHC soil. After the cuttings struck, I eliminated all but the three strongest in each of the 4 containers. I watered each container with a weak solution of MG 12-4-8 with STEM added at each watering, and watered on an 'as needed basis', not on a schedule. The only difference in the fertilizer regimen was the fact that I included a small amount of MgSO4 (Epsom salts) to provide MG (the dolomitic lime in the bark soil contained the MG, while the gypsum (CaSO4) in the CHC soil did not. This difference was necessary because of the high pH of CHCs and coir.) for the CHC soil.

The results were startling. In both cases, the cuttings grown in the CHC's exhibited only about 1/2 the biomass at summers end as the plants in the bark mix.

I just find it very difficult for a solid case to be made (besides "It works for me") for the use of coir or CHC's. They're more expensive and more difficult to use effectively. The fact that some believe peat is in short supply (no where near true, btw) is easily offset by the effect of the carbon footprint of coir in its trek to the US from Sri Lanka or other exotic locales.

That's the view from here. YMMV

Al

Thanks

How much gypsum should I add to an expanded block of coir, the same block in the link.

---How much gypsum should I add to an expanded block of coir, the same block in the link.

Hard to say. This is why (blurb from the link): Sunleaves Classic Coir Block is a compressed coconut-fiber growing medium that expands to approximately 2 1/2 cubic feet when soaked in water. Expanded contents of SCCB310 will fill approximately 30 one-gallon nursery pots.

Ok, let's break this down. 1 cubic foot equals 7.5 gallons.

The first statement says it expands to 2.5 cubic feet. That would be 18.75 gallons. The next statement says it will fill 30 one gallon pots. So, is it 18.75 gallons of volume or 30? LOL.

Figure 1/4th-1/2 cup per cubic foot. I will leave it to you to determine how much volume the brick really constitutes.

Thanks

I would tend to want to err on the low side if you err .... because of coir's low bulk density.

Any reason you don't want to use peat?

Al

No reason really. I just thought of trying coir this year.

OK - I like peat much better, but of course it's your soil. ;o) Add 1 level tbsp of gypsum per gallon of soil or a skinny 1/2 cup per cu ft. Because you should use gypsum as a Ca source in coir-based soils, you'll need to use MgSO4 (Epsom salts) as a source of Mg, and so the Ca:Mg ratio isn't so skewed that you create a Ca-induced (antagonistic) Mg deficiency. Use 1/8-1/4 tsp per gallon of fertilizer solution every time you fertilize, or every other week if you're attempting to insure nutrients via organic soil amendments.

Al