Green thumb?

Two weekends ago I got an urge to have colorful plants out on the balcony. I trucked on over to OSH and bought all the fixings for a cute floral window box-type planter: potting soil, planter, various flowering plants, plant food, and a trowel. I passed on the gardening gloves, because all these delightful things were adding up and I decided that I wasn't going to be digging all that often anyway. I took a picture of them right after I planted them just in case I killed them all and they just deteriorated into brittle death.

Before...

Sadly, I do think that some of them have started to deteriorate. They're looking a little limp-ish. Lots of the snapdragons in particular are dying, and I can't see any new buds opening. But some of the white pansies seem to be loving it. I made sure they had enough water, and even gave them some MiracleGro. Maybe I overwatered? Part of the problem is that I haven't a clue what I'm doing with this whole container gardening thing. I might have to break down and buy a "dummies" guide before I try to repair the damage. I haven't taken an after picture because I'm still hoping that they bounce back. Updates to come.