is miracle gro's organic potting soil fine just for potting plants in planters in a terrarium.
After being pressed by a dear friend to try/evaluate CHC's, I performed a little experiment. Below, is a copy/paste job from a post I left somewhere, earlier this year. Though it starts out talking about coir, it ends with some commentary about CHCs.
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 or CHCs as the primary component of soils virtually eliminates lime or dolomitic lime as a Ca source because of their high pH (6+). Gypsum should be used as a Ca source, which helps correct coir and CHC's low S content. All coconut 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 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 several times, I made a 5:1:1 soil of pine barkeat
erlite (which I know to be very productive) and a 5:1:1 mix of CHCs
eat
erlite. 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 summer's end as the plants in the bark mix.
I just find it very difficult for a solid case to be made (aside from "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.