This is a love hate sort of plant. It provides wonderful blue color in the fall and looks so good at that time I would never want to be without it, but the rest of the summer I am hacking away at it so that it won’t gobble up the garden. The plant emerges late in the spring as small attractive green leaves and slowly grows to its full size of 3’, flopping and spreading all the time. The flowers that will appear in the fall are very welcome because few other blue flowers are blooming then and they go well with the mums and other fall flowers that you may have blooming. Cutting them back every few weeks to make them more tidy is well worth the effort and I am always glad that I have this plant in my garden.
Type: Herbaceous perennial.
Bloom: Numerous small azure blue flowers are borne in dense fuzzy-looking clusters on top of 3’ floppy stems in late August through fall.
Light: Full sun.
Soil: Moist, well drained soil.
Hardiness: Zones 6-10.
Care: Cut back once or twice during the summer to encourage bushier plants and less floppiness. Grow near plants that can provide some support in late summer/fall.
Pests and Diseases: None of importance.
Propagation: Hardy ageratum is rhizomatous and spreads quickly so divisions in spring are easy and successful. Cutting can be rooted.
Companion plants: Sedum ‘Autumn Joy’, Aster tartaricus, Aster novae-angliae ‘Alma Potschke’, Purple Muhly grass (Muhlenbergia filipes).