I've never tried coir. Seems to me it might hold a lot of water and stay awfully wet. Is that true? That's what I have against seed starting mix. Those I've tried just seemed heavy, very fine texture, held a lot of water and stayed too wet for my liking.
A good peat based regular potting mix works so well for me that I'm reluctant to change. Sort of the old "if it ain't broke don't fix it" mentality.
Karen
