What summer- and fall-blooming perennials have blue flowers?

Question:

What summer- and fall-blooming perennials have blue flowers?

Answer:

Several perennials have blue blooms that appear between early June and September.  They include: 

Summer and Fall Blooming Perennials with Blue Flowers (listed by approximate bloom time)

Common Name	Genus	Size	Light	Comments
Catmint	Nepeta x faassenii	12-24	Sun	Blue or white flowers in early summer; long blooming
Perennial geranium	Geranium hybrids	12-36	Sun-part shade	Blue flowering cultivars in early summer; long blooming
Spiderwort	Tradescantia species and hybrids	12-36	Sun – part shade	Some species native to US; blue, lavender, pink, white flowers
Perennial Sage	Salvia xsylvestris	12-48	Sun	Blue, violet, pink, or white flowers
Lupine	Lupinus hybrids	12-36	Sun	Some species native to US; hybrids with blue, white, red, pink, purple, and yellow flowers
Carpathian bellflower	Campanula carpatica	6-12	Sun	Blue, purple, white flowers
Clustered bellflower	Campanula glomerata	12-24	Sun	Clusters of blue, white, or purple flowers at stem tips
Peachleaf Bellflower	Campanula persicifolia	12-48	Sun	Bell-shaped flowers in blue, white, pink, and purple
Delphinium	Delphinium hybrids	36-50	Sun-Part sun	Large blue, white, purple, and pink flower clusters
Lobelia	Lobelia siphilitica	24-36	Part shade- shade	Native to US; blue flowers; short-lived; spreads
Pincushion flower	Scabiosa hybrids	10-18	Sun	‘Butterfly Blue’ is a popular cultivar with blue/lavender flowers
Spike Speedwell	Veronica spicata	12-36	Sun	Deep blue, white, or pink flowers
Globe thistle	Echinops ritro	24-48	Sun	Globe shaped flowers in blue, blue/gray, and white
Sea Holly	Eryngium amethystinum	24-36	Sun	Thistle-like flowers in blue, purple, or blue/gray
Balloon flower	Platycodon	12-36	Sun	Balloon like flower buds in blue/violet, white, and pink
Lavender	Lavendula angustifolia	12-36	Sun	Select cold hardy cultivars; well-drained soils essential
Bluebeard	Caryopteris	36-60	Sun	Blue, lavender, or white flowers; variegated foliage on some cultivars
Bottle gentian	Gentiana andrewsii	12-36	Sun-part shade	Native to US; blue or white flowers that never fully open; late summer
Russian Sage	Salvia yangii	36-60	Sun	Formerly Perovskia atriplicifolia
Stokes Aster	Stokesia laevis	12-24	Sun	Native to US; Lavender, blue, cream, or yellow flowers
Monkshood	Aconitum carmichaelii	36-60	Sun - shade	Blue, white, or bicolor flowers that are hooded; poisonous

Learn more in this article: Blue Blooms for the Midwestern Garden.