Allium aflatuense 'Purple Sensation'.

Invaluable for some colourful height in the border.  As the flowers emerge, the foliage dies back so any alliums need to be planted in between other leafy perennials so that the dying foliage is hidden from sight.  Wonderful purple round heads perform for weeks depending on the weather, but a must for a spring/summer border.  Other alliums do flower later, and the addition of these will give a continuous show of colour.