It looks like they need to dry a bit more between waterings. They like to be so much drying than you expect. Let soil get dry, up to your top knuckle before watering.

Thanks, Laurie! My first reaction was too much water, but the dried/dead flowers made me wonder. They have always done so well in this planter, but now everything in the middle has died. Only the plants on each end are surviving.

I'm going to have to investigate the drainage and soil. I had planted snapdragons last fall and they all died - quickly - but had done well in previous years. Seedling zonals died, too.

There are drainage pipes on the other side of this planter. The leaf cutter bees like them for housing their young. Something is up with this planter. I'll get to the bottom of it even if that means literally digging out all the soil.

Thanks! I'll stop watering and see how things go.

How high is your summer temperatures in this part of Florida? Check the drainage first, but dont exclude high temperatures. I had that seemingly similar symptom affecting all my zonals and ivies at the same time of the year. I posted my pictures here: http://forums.gardenweb.com/discussions/4154782/heat-stress-or-disease and the end of summer had finally given me an answer. Unfortunately, few had a tip rot which went down to the root. Many others were pruned and had those rotting tips cut-off before that happened.

Now the heat is behind us. Active growth heals the damages of summer, backed-up by fertilizing regime. It's all green again but there is still a long way to go. Those which made it through the summer will provide the seeds for the next generation. More heat-tolerant specimens are on the lookout and may provide further genetic diversity.

I think it was the heat, too. We were pretty consistently in the mid to upper 90s. I have a couple of plants still living, but the others had rotting tips that spread rapidly to the roots. Pruning didn't help after it had started.

Before planting anything for the fall I am going to dig around, loosen the soil and see if it is compacted or needs replaced and add a good portion of grit (probably perlite). I haven't worked on this soil for a few years, so that can't be helping. The drainage pipes were clear, but it may still be slow draining.

I've collected seed, so we'll see how things go this winter. Last year all that was available was some pink flowered plants. I'm not a fan of pink, but maybe they will hold up better.