Plants that bloom in September in Zone 4 with blue flowers

Anise Hyssop

Lavender-blue spikes with licorice-scented foliage. A pollinator powerhouse that blooms for months.

Aster

The grand finale of the garden season. Essential for fall pollinators.

Big Bluestem

The signature grass of the tallgrass prairie, turning copper-bronze in fall with distinctive turkey-foot seed heads.

Borage

Star-shaped electric blue flowers that bees go absolutely wild for. Self-sows freely.

Cat's Meow Catmint

Tidy, dome-shaped habit that never flops open. Stays compact without shearing.

Catmint

Billowy lavender-blue haze that blooms all season if you shear it back.

Clematis

The queen of flowering vines. Over 300 species, something for every spot.

Endless Summer Hydrangea

Reblooms on old and new wood, so you get flowers even after a harsh winter. Color shifts with soil pH.

Great Blue Lobelia

Intense blue flower spikes that hummingbirds and bumblebees fight over in late summer. The bolder, taller cousin of cardinal flower.

Monkshood

Deep indigo-blue hooded flowers on tall spikes in late summer. One of the few genuinely blue flowers that grows in shade.

Morning Glory

Fast-climbing vine with trumpets that open fresh every morning.

Pickerelweed

Spikes of violet-blue flowers above glossy arrow-shaped leaves. Native pond and stream bank staple.

Prairie Sky Switchgrass

The bluest foliage of any switchgrass, with airy pink seed clouds drifting above in late summer.

Russian Sage

Airy lavender clouds on silver stems. Thrives in heat and poor soil.

Salvia

Vertical flower spikes that hummingbirds and bees cannot resist.

Sea Holly

Metallic blue bracts and cones turn the whole plant a vivid silvery-blue. Otherworldly and completely drought-proof.

The President Clematis

Big, rich violet-blue flowers with silvery reverse petals rebloom through the season on a vigorous, reliable plant.

Walker's Low Catmint

Perennial Plant of the Year. Billowy lavender-blue spikes that rebloom hard after a shear.