Poorly pansies.

I planted some good quality winter/ spring pansies in Autumn and put them in some little beds that were created on top of a stone wall - see picture. Some of the beds already had rockery-type plants in them which were and still are growing ok. Apart from an initial bit of slug and snail damage which I treated and a few unexplained losses they managed over the winter. Since then I've lost some more and don't know why. Some had died off in the centre but have a side stem which is ok but not great yet some right next to them are doing really well with lots of flowers. Anyone know what is the cause of this?

...and perhaps also look for signs of fly/aphids on them too, they can finish them off quickly!

It might be a bit dry/exposed for them on top of a wall, particularly as it's been a dry April.

Photo of an experiment I've been doing below, planted in late Autumn. A trailing pansy in the middle, and trailing violas either side. Both violas have done better than the pansy, and you get a scent from them. They were all fed with tomato food to start with, then a seaweed extract, and dead-headed early on.

G&R