Can coconut coir be substituted for peat in the 5:1:1 mix?
I'd rather use coconut coir for sustainability reasons when compared to peat.
Generally, commercial ops try to keep coir to less than a 10% fraction of the o/a mix because of its high pH, salinity, and high K content. If you're intent on using a more significant fraction, you might wish to eliminate half or all of the lime and substitute gypsum for the portion of lime not used.
FWIW - I think people are being sold a bill of goods on that whole 'peat/sustainability' thing.
Some things I've offered before on peat vs coir and the sustainability of peat:
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 high in soluble salts, so this can also be an issue.
Using coir as the primary component of container media virtually eliminates lime or dolomitic lime as a possible Ca source because of coir's high pH (6+). Gypsum should be used as a Ca source, which eliminates 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 interfere with the uptake of Fe.
I have done some testing of coir and 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 or 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
Peat - Renewable or Not? - Does it Matter?
Chicken Little would be aghast at your inference!! In my estimation, it doesn't matter much if it's renewable or not, and I refuse to be made to feel guilty about using any form of peat.
Here is a reply I often leave when the non-renewable thing comes up:
"Sorry, but I'm not buying the non-renewable lament. In Canada alone, there are more than 270 million acres of harvestable peat bogs. If we make the conservative guess that the harvestable portions of these bogs are 10 feet deep, that means there are probably more than 900 billion cu. ft. available for harvest, just in Canada! That doesn't even take into consideration what's available in Europe, Asia, or places like New Zealand where they also mine peat. Canada currently has mining/harvesting operations underway on approximately 40 thousand acres or about .014% (that reads 14 one thousandths of 1 percent)."
Check the math - it's accurate and conservative. It's more likely that the next ice age will be upon us and glaciers will have covered what's available before we even use a noticeable percentage.
Renewable/non-renewable = moot.
I agree with Al... and, I've used cocopeat before with less than satisfactory results. It's not a product I would recommend, not even as a partial portion of a medium.
Knowing what I know about the goals and marketing methods of most industries, I'd agree with Al that there's no peat shortage, and we're only doing opposing industries a favor by believing the hyped propaganda. How can coco coir products be "green" if they leave a large footprint in processing and shipping?
Coco coir products tend to hold more moisture than I want, for a much longer time frame than I want, and when I used it, it grew the most amazing and unique molds I've ever seen... scary molds in technicolor.
Even the pre-rinsed cocopeat required overnight soaking and repeated rinsings before the water began to run clear, indicating anything used in its processing was removed. It's a highly saline item, due to processing, I believe.
When it first gained popularity, a couple of my gardening acquaintances were using it and said I should try it, though I should have asked why. I should have done my research, and asked how it worked and what its properties were.
I abandoned using it when my bulbs and other plants and their roots began rotting from the prolonged amount of time it remained saturated, and I saw roots actually turned up, growing toward the surface and pot sides in search of oxygen. Cocopeat tends to compact fairly quickly, too... I noticed a full pot decrease to a half pot full in less than one year. That's not good.
Personally, I'd go with the regular old peat we all know and love... and I'd avoid an item that's fairly new to the industry, at least until it can be proven as a positive addition. And after what I experienced, you couldn't prove it to me.
I'm but one grower in millions, though... so the choice is up to the individual. Keep in mind, though, knowledge is always key.