I like beurmann's idea of sending out a sample to be tested for nutrient levels and excess salts. He left links to several local testing companies and generously offered to split the cost. The first test is on me, if this gets expensive I'd be happy to take him (you?) up on it.
One the same subject, thanks, too, to our friends at Homegrown Evolution for pointing me to a great, cheap testing lab for any kind of garden soil -- UMass Soil Lab. I tried calling them to ask if testing for excessive salts in coir was possible and was asked to leave a message in a full voicemail box.
I'm a little confused by what kind of test I need to have done. Take a look at one company's menu of testing options. Does coir even count as "garden soil"? A phone call to one of testing companies might clear things up.
In any case, it looks like I'll need to amend my coir with garden gypsum and epsom salts to get a soilless mix that transfers nutrients to my plants. From "tapla" at the GardenWeb Container forum -
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.He, "tapla", gives some specific directions on how to amend the coir later in the same thread -
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.
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.
More information that suggests that adding gypsum is the way to go -
Coconut coir, a by-product of the coconut industry, has been promoted as an alternative to peat moss in soil-less media. Sphagnum peat moss has long been a standard component of soil-less media, but some people have expressed concern that it is a non-renewable resource. Although it does not appear that world peat resources will be in short supply for a very long time [nevermind the habitat loss and release of sequestered carbon, ed.] , coconut coir may have characteristics that make it a useful component of soil-less media mixes. Coir has been considered to promote excellent plant growth but there are few rigorous studies that have compared it with peat moss control plants. However, ten years ago, Meerow (1994) found that growth of Ixora coccine was significantly reduced compared to growth in a sphagnum peat moss control. Vavrina (1996) found that there were no adverse effects of coir to tomato and pepper transplants, but a subsequent study in the same lab (Arenas et al., 2002) found that media with more than 50% coir had reduced growth compared to peat-grown control plants. They suggested that a high N immobilization by microorganisms and a high C:N ratio in the coir may have caused the reduced growth. Lopez-Galarza (2002) found that root development of strawberry plants grown in peat moss was better than in coir in some, but not all, studies. Handreck and Black (2002), in a comprehensive textbook on soil-less media, review the chemical and physical properties of coir dust that are being sold in Australia. They indicate that since all coir products have extremely high K contents and low Calcium contents, it is critical to add a source of Ca to improve plant calcium uptake. Since the pH is already close to 6, liming materials cannot be used because they would increase the pH above optimum. Handreck and Black says that “Therefore, all coir-based media must be amended with gypsum, which also overcomes their low sulfur status.” [emph. added] Ma and Nichols (2004) recently reported that the problems with coir extend beyond its high salinity. Their data indicate that high concentrations of phenolic compounds in fresh coir are at least partly responsible for the growth reductions observed in other studies. Several studies at the USU Crop Physiology Laboratory indicated that monocots grown in coconut coir were extremely chlorotic and stunted. The objective of this study was to see if there are differences among plant species and types of coconut coir compared to growth in sphagnum peat moss.