Eupatorium coelestinum (Hardy Ageratum) ‘Wayside’

I have always loved Ageratum, but have been unable to keep it looking good for any period of time. By mid-summer, they are a mess, I cry and vow to never put myself through that ordeal again. Fool me once …

Lo and behold, one day I was googling “Ageratum” thinking I could unlock the secret to keeping this annual alive all summer and found a plant claiming to be a perennial Ageratum. What? Has someone been reading my diary?

Dreams do come true.

But it gets better. This plant prefers a wet site. And is deer resistant.

Hardy Ageratum? I’m like totally in.


  • 18” x 18”
  • Blooms in mid-summer, early August here in zone 6B
  • Requires full sun
  • Survives zone 5-8
  • Deer resistant
  • Very tolerant of a wet site
  • Very slow to emerge in spring, one of the last to show signs of life
  • Great winter interest with the spent flowers
  • U.S. native
  • Has recently been reclassified as Eutrochium

As mentioned above, this plant is slow to emerge in spring and I’ve actually forgotten about it until it finally emerged sometime in late April. Another reason to not cut down those perennials too soon people. The spent flowers/stems are a much needed reminder of what is what in my ever expanding jumble of a garden in spring.

I’ve noticed that my original five purchased have expanded a bit in year two as this plant appears to reseed some. It is too soon to say if it is TOC (Totally Out of Control, for those without young kids) or if the reseeding is a must because this perennial is short lived. That is what I’ll be keeping my eye on this year.

The blooms start to develop in July and are a welcome site and color, as we proceed through the dog days of summer.


Within a week or so, the blooms fully emerge and they are quite stunning in my humble opinion.


The blooms are so interesting up close that I’ve taken to capturing them on my camera phone, macro style.


But the interest in the blooms doesn’t end there. As the purple/blue flowers fade with the arrival of cooler weather, they remain interesting into the colder months.

Here in October, fluffy seed heads looking right in place with the gold and red hues of autumn.


And especially handsome when covered in frost.















10 thoughts on “Eupatorium coelestinum (Hardy Ageratum) ‘Wayside’

  1. Leslie Hyman

    It’s a beautiful plant, but does expand almost TOC, and should be used more like a groundcover. It does not co-exist with other plants very nicely.

    Also, it is not tolerant of occasional standing water wet areas, just fairly moist soil areas.

    1. jmarkowski Post author

      Thanks for the feedback Leslie! I’n very curious to see how this acts this upcoming season. I really do love it and I can afford some aggression, assuming it comes back all together. It is in a very wet area.

  2. Jeff Powell

    I’ve been concerned about it being a thug in the garden, and a bit invasive too.
    Glad to hear that it’s well-behaved so far.
    Keep us posted!

    1. jmarkowski Post author

      Thanks Jeff! I will be sure to keep you updated. A lot of “thug” comments here so I am a bit concerned.

  3. suz

    it gets TOC here, especially with the damp, and does not play well at all with others, as leslie said. so i really have to keep after it, but the late-summer bloom when nearly everything else is gone makes it worth my time. at least it’s the only labor-intensive thug i have. –suz in ohio

    1. jmarkowski Post author

      Thank you Suz! A lot of TOC feedback so I may have my work cut out for me this season.

  4. Linda o'Connell

    This sounds very appealing, John, and I doubt if it will be invasive here with our cooler summers. Fir that color, it’s worth a try.
    Linda on Whidbey

  5. Deborah

    I find the Hardy Ageratum/Blue Mistflower to get TOC as it does creep rapidly by rhizomes through my garden areas.
    Popping up more where I don’t want it during the summer. Though do welcome the blue/purple in late summer/early fall.

    1. jmarkowski Post author

      A very common theme in the comments Deb. Color me worried, even if the color is sweet.

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