Sorry, Allison. But one time isn't a fair trial. We all have an attempt or two that doesn't work, doesn't matter if with coir or potting mix.
Most of my original coleus cuttings are huge now, root bound in 4" pots. A few that were big, healthy plants last summer are barely surviving. All are potted in ProMix. I have no idea why my duds are duds. I should have repotted them, but haven't. They're going to go right into the ground like everyone else and they can sink or swim. If they sink, I'll be on the coleus forum begging cuttings in the fall.
Besides, do you still have a truck load of coir?
Karen