Further to my posting (The Scoop on Dirt), I had read about peat moss having initial problems with dryness, but I think I didn’t quite “get it” until I saw it in action.
It’s no big deal to fix. If you use an 80% peat / 20% perlite & vermiculite (or similar pro-mix) in a sub-irrigated planter, where the water comes up from underneath, make sure you water the top of the planter generously a couple of times a day for a couple days, until you see that the peat at the top level has expanded and is retaining a fair amount of water. It will be visually obvious when its properly wetted… there will be dark, moist looking spots that stay put all day. You’ll likely notice it around the feeding pipe first. Just keep going in the areas that aren’t until they match.
It looks like, generally speaking, the moisture level at the top of my planter is holding well now… at least where I have plants and there’s some shade. It’s a little bit dryer (but not bad) where there’s seeds planted and the dirt is bare naked exposed, so I’m still giving it a quick sprinkling in those areas to make sure the peat doesn’t dry out fully and my seeds have enough water to germinate with.