Although UMD Extension doesn't have any fact sheets about coconut coir (yet), we consulted with one specialist that has some experience with different potting media that commercial nurseries use. Coco coir processing has a large impact on the material's end quality and water-holding capacity and aeration, at least in comparison to peat moss. Overall, when used at a coarseness grade similar to that of typical peat in a potting mix, coir tends to hold more air and less water. This is not necessarily a good or bad trait, as adjustments in crop needs and irrigation practices can greatly influence how successful or not any given plant species will be in either substrate. Do look for coconut coir that is processed to have the lowest salt contamination possible, as this is another trait that might vary considerably from one manufacturer, source, and even batch to another. Some growers mix coir with peat, in order to use less peat overall but retain some of the familiar attributes of that material, but you may need to experiment if you want to use coir for seed starting or container plantings to see how it works with your style of cultivation (how often you're watering, fertilizing, etc.). Some plant species might be more picky about substrate properties (moisture or nutrient retention, for instance) than others.

Miri