There is a lot of purple in May and early June. Here are four purple-flowered plants, two natives and two not, that have done very well. They will all take light shade, although the geranium would probably be happiest with more sun than the others.
False Indigo, Baptisia australis
This native plant erupts from the ground the second week of May, and is blooming by the end of the month! It is very popular with our bumblebees.
The flowers form pods that dry to a very dark gray with dried seeds rattling around inside. They will seed in if you do not remove the spent flower stalks. I tend to just weed out the sprouts—the pods are good conversation starters.
American Wisteria, Wisteria frutescens
I have had this plant for several years in what would be considered a difficult spot for it—drier than the ideal—but it blooms a bit more every year.
It shares the arbor with an autumn clematis, which seems to get a just a bit more than half of the space. The arbor is within the dripline of the enormous silver maple that overhangs my yard, so the vines on it get sun until early mid-afternoon.
Geranium, Johnson’s Blue
This is a tidy, well-mannered hybrid—it does not fling seed around like the native geranium does.
Columbine, Aquilegia olympica?
This commonly referred to around here as the Old West Side Columbine. It seeds in, but not obnoxiously. The plants are easy to pull or move, although they move better when they are small, as they have taproots.
They start blooming in mid-May, and you can extend the bloom a little by removing the developing seedpods. If you leave them, they will shatter, and there will be plenty of baby columbines to follow.
These do much better than the native columbines, which tend to struggle in this yard. Too bad; I like both.