Particularly Purple

 Siberian iris are often a rich blue-purple.  They are happy growing in moist soil in sun or part-shade and are very cold hardy.  Plant a few bulbs, and they will gradually grow into a generous clump. Beautiful by a pond if you have one.

 Bearded iris are always interesting, but they do have a tendency to fall over in wind and rain.  A poorer, sandy soil can keep the growth in check, and make them less floppy.

 Floss-flower (Ageratum) is a tidy plant that can be easily tucked into any empty spots in an annual
 bed, or in a planter box or hanging basket.  Not many flowers come in a soft lilac colour like it does, and it looks lovely paired with lemony yellow flowers . Also works well with other purple or pink flowers.

 Morning glory flowers only last a day each, but they are so pretty.  I was trying to think of a place where they could climb, and finally settled on running some strings down from the apple tree branches.  The morning glories are planted in pots at the bottom of the strings.  The light is not optimal, but it is enough for some blooms.

 Sun shining through an iris. I know, it's really more pink than purple.