This classic passalong plant provides weeks of late color.

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Wild Ageratum Shrub
Credit: Steve Bender

Wild ageratum (Conoclinium coelestinum) is a great reminder that gardeners should always have lots of like-minded friends. That's because you will never find this Eastern native in a garden center. People typically acquire it from folks who generously share a piece. Don't fret, though, if you don't have any gardening friends. You really have one – me – and if you read on, I'll provide an alternate source.

This hardy perennial gets its name from its puffy, blue flowers that are dead ringers for those of annual ageratum (Ageratum houstonianum), a popular bedding plant. It grows into a multi-stemmed mound from 18 to 36 inches tall. ‘Wayside,' a more compact selection, tops out at 15 inches tall. Blue blossoms first appear from mid- to late summer and continue through the fall. Butterflies like them a lot.

Wild Ageratum Blooms
Credit: Steve Bender

In my first book, Passalong Plants, I wrote about wild ageratum in a chapter titled "The Ones That Get Away." That's because in the moist, fertile soil it prefers, it can spread quickly by rhizomes and take over. Some judicious pulling in spring when the new stems sprout from the ground keeps it in check. Plant it in full to part sun in USDA Zones 5 to 10. Deer seldom eat it.

Still no friends to share it with you? Order online from Bluestone Perennials.

Here's hoping for beautiful blue blooms next summer.