Penstemon, one of the larger flowered ones eg Czar, or there are some nice blue ones if you want to stick to the same colour as the thistles? Odd that the geranium went brown though, they are usually very tolerant. Have you checked for root pests?

Thanks steragram,
well that's what I thought, I looked at the roots on the thistle as I thought that's where the problem was but I am not sure what to look for. I will have a look at the penstemon but I have red one the other side of the blue geranium.

Penstemons -Well there are pink ones and white ones as well - look at Wedding Day. Look for caterpillar type grubs in the soil -little C shapedvine weevil nes and more caterpillar sized cream with brown heads - never sure what they are but they eat roots. (No idea if they might be the trouble but worth a look)