Hardy Ageratum, Blue Mistflower
Conoclinium coelestinum (L.) DC. is the accepted scientific name for the Hardy Ageratum. It was named and described as Conoclinium coelestinum by Augustin Pyramus de Candolle in Prodromus Systematis Naturalis Regni Vegetabilis in 1836. It was FIRST described as Eupatorium coelestinum by Carl von Linnaeus in Species Plantarum in 1753.
Version 1.1 of The Plant List updated in 2013 lists only four accepted species of Conoclinum. The new Plants of the World Online by Kew lists it as an accepted genus but lists no accepted species. They were new in 2017 and are still uploading data. I checked the genus Eupatorium just in case and they say it is accepted but also list no accepted species for the genus. I checked both names with the World Checklist of Selected Plant Families (also by Kew) and both times came up empty.
I went to Tropicos to see if they had an opinion as to which name was accepted. Both names have a “!” in front which means it is the legitimate name. BUT, the synonym listed for Eupatorium coelestinum is Conoclinium coelestinum. How can both names be legitimate? The Missouri Botanical Garden is using the name Conoclinium coelestinum so that is good enough for me. Tropicos is maintained by the Missouri Botanical Garden.
Over the years many plants have gone by several scientific names depending on where you look.
The Missouri Botanical Garden and Royal Botanic Garden-Kew were working in cooperation to build and maintain The Plant List. The Plant List hasn’t been maintained since 2013 and Kew started Plants of the World Online in 2017. They are still uploading data and hope to be finished in 2020. Of course, it will always be a work in progress.
I think probably, as with many genera, the botanists may be in a little disagreement about what species go where and what genus to use. Perhaps they will put it back in the Eupatorium genus since that genera was described in 1753 and the Conoclinum genus wasn’t named until 1836. Maybe they will do testing to find out eactly what is what.
There are many Ageratum cultivars, both annual and perennial, that are available. My dad happened to get his Hardy Ageratum start from Aunt Inez, his mother’s sister, who lived in Holden, Kansas many years ago. Good thing they still come up and spread a little every spring.
Sometimes I name plants after where they came. So, I call this plant Conoclinium coelestinum ‘Aunt Inez’ after my aunt.
2013 was my first experience with this plant after moving back to the family farm in February 2013. They do pretty good here and return every spring. They came up better on the east side (left side) of the steps so I always have to transplant a few to the right side. They came up pretty good in the spring of 2013, even under the steps.
I didn’t take many photos in 2014 and none of the Conoclinum coelestinum.
They aren’t the first perennials to start coming up so you may have to be patient. The plants that grow from seed take even take a little longer. They mostly come up from seed unless we have a very mild winter.
One thing is for sure, though, they will grow and put on an AWESOME show!
ORIGIN: Central and southwestern United States and the West Indies
ZONES: USDA Zones 5-10
SIZE: 18 to 36” x 18-36”
FLOWERS: Produces blue flowers from July through October
LIGHT: Full sun to part shade
WATER: Average water needs. Drought tolerant once established. They will grow in wet areas.
MAINTENANCE: As the plants get tall they have a tendency to flop and may need support. SO, they can be
USES: Beds, borders, attracts butterflies and other pollinating insects.
PROPAGATION: These plants spread by rhizomes, sometimes aggressively. They can easily be transplanted by digging the rhizomes in the spring. They also self-sow.
Once they start coming up pretty good, I always space them out a little more. Sometimes A LOT come up and sometimes not. Like I mentioned earlier, more come up on the east side of the steps and I always transplant some on the west side.
In July they will start to flower and will soon be covered!
Butterflies and other pollinating insects love the flowers. The butterfly in this photo is a Pearl Crescent (Phyciodes tharos).
The winter was pretty mild, so A LOT of the Conoclinium coelestinum came up in the spring of 2017. We always have a few Knotweed or Smartweed (whatever you choose to call them) that come up here, too. They are easily removed.
They seemed to grow taller in 2017.
They were just beginning to bud and flower when the above photo was taken on August 7, 2017.
Sometimes we take the beauty of flowers for granted and fail to take a closer look.
January 2018 was very cold and as of May 20 I had only seen one of these plants come up. It was a dry spring which may also be one of the problems. Normally I cut the dead stems off and lay them over the area they grow in which allows their seeds to fall off there. But, last fall, I didn’t do that and didn’t cut them off until April. They had grown tall and flopped over in 2017, so maybe their seeds fell off in the grass during the winter.
If only one plant comes up, it will be difficult to get this plant to come back well. It may take some time.
Several Conoclinum coelestinum finally came up on both sides of the steps.
It was strange not having a mass of these plants on both sides of the steps in 2018 like there usually are.
The Conoclinum coelestinum looked really good with other plants like the Gomphrena globosa ‘Gnome White’.
I will have to do things a little different this fall when I cut the some of the perennials back. I will cut the Conoclinum coelestinum and lay the dead stems where I hope more will come up next spring.
Overall, the Blue Mist Flower is a very good perennial to grow in a sunny area when it can get plenty of moisture when needed. I haven’t noticed any insect problems which is a plus. The grasshoppers don’t bother them even though we have plenty. This year, 2017, we had a terrible Japanese Beetle population that seemed to be everywhere. They ate the flowers of the roses but did not bother these plants.
There are two problems I have noticed, though. One is that if they are allowed to grow freely, they get tall then flop over and sprawl. This can be a problem if you have other plants in front of them. You can cut them back which will probably help, although I have not done this yet. Maybe next year. The second problem is sometimes they have an issue with powdery mildew. It doesn’t seem to harm the plants, but it just looks bad.
The other thing you have to consider is that they not only spread by rhizomes, they also self-sow. SO, they don’t necessarily stay where you want them. The good thing is that the seeds don’t seem to go far. They come up under the steps and deck a little but not that bad. Just keep in mind, if they like where they are growing, they could become invasive. Just give them ample space to do as they please, and you will be pleased with them
I hope you enjoyed this page and maybe found it useful. If you have any comments, questions or suggestions, I would like to hear from you. Please click on “like” if you visited this page. It helps us bloggers stay motivated. 🙂 You can check out the links below for further reading. The links take you directly to the genus and species of this plant.