Looks like they're in part shade now, but how much sun do these get? Could it be that you planted them last year after the trees had leafed out providing more shade, and now the hot April sun got to them before the trees could shade them properly?

It could also be a fungus, and looking at it again, I would say they've been pretty devastated by it. You could attempt using some fungicide on them, but at the current state you'll likely be fighting an uphill battle.

They get some morning sun but are mostly in the shade.

gdpossehl: what would be some signs that it's a fungus?

http://msue.anr.msu.edu/news/signs_and_symptoms_of_plant_disease_is_it_fungal_viral_or_bacterial

Agree, need more sun!

It could also be water as you mulched around them which is great but with the overhang of the roof and a sandy soil the root system may have never gotten outside of the pot zone and thus the plants became top heavy. I would prune them back solid, water, and add some composted manure. You could also move them in a last ditch effort.