A compressed block of coir: fiber from coconut shells
Both Bruce and I have used some coir, along with a larger quantity of peat and a little perlite, in previous years, but haven't yet tried all-coir as planting mix.
Coir seems to retain more moisture, and in a covered SIP like the ones we use, we're concerned about soggy growing medium.
Covered SIPLeave info in comments or email us. And thanks...