I'm happy to see more and more gardeners putting videos of their gardens on youtube. There was a time when searching "Liatris" on there only resulted in bad songs, each one worse than the last! Here though we have several people sharing their experience with one plant in particular. Liatris ligulistylis.
When viewing this video one gets the idea that Monarch butterflies are abundant. In truth the plants they're frolicking about are one of their favorite nectar plants, Liatris ligulistylis. This plant likes growing in modest to slightly wet conditions but not to wet. They bloom around August just before the Monarchs start their migration southward. Of the four generations this is probably the largest generation of Monarch to be born so it's all the more likely a Monarch will be fluttering around the plant.
Monarchs are somewhat in danger as this past year was said to be the smallest population of them yet. Illegal logging, particularly cold winters, among other things have limited their over wintering forests from 20 acres to 4.5 acres. (The New York Times article that reported this has since expired sadly.) To help them out it's best to include their host plant, Milkweed in the garden.
Asclepias species combined with this Liatris is an excellent combination. I planted a try of 20 or so plants last year however, the nursery I bought them from kept them in green house conditions a little to long. So they didn't come up at all. Presumable they will come up this year though.