Ceratostigma willmottianum

Ceratostigma willmottianum. 
Left - the soft rounded habit, up to 80cm wide and high, is used here nestled amongst the spikey plants to create a foil for the sharpness of the yuccas and palms. The blue colour of the flowers has a peculiar intensity that lightens up any planting scheme, here setting of the dark greens of cypress and palm and grey tones of the yucca. Originally from Szechwan in China where it grows in rough sunny ground in rocky places with some limestone present. It flowers from late summer and will keep going until the frosts when its stems may be cut back to ground level in a severe winter.
Ceratostigma plumbaginoides.
Right - Its common name of 'Hardy Plumbago' is certainly apt as the structure of the flower cluster and buds is very similar. This species is the same in most respects but is slightly lower growing with more intense blue flowers. It may be slightly less hardy meaning that it will always be cut back to ground level.