A classic annual for any garden, ageratum is a tough plant that can even handle a bit of shade. Not to mention, ageratum is one of the truest blue annuals you can find! Characterized by their powder-puff flowers, these plants begin to bloom in late spring and keep the show going until the first frost. These are some rugged plants that can withstand tough soil conditions and even deer! However, all parts of this plant are poisonous if ingested, so site ageratum carefully if you have small children and pets around.
Sometimes referred to as a floss flower, ageratum has playful, small blooms that look like tiny pom-poms covered with floss-like filaments. They are known as one of the best annuals for cutting. Ageratum has been grown for years, primarily because it offers a rare color in the flower world: blue. This makes the flower perfect for patriotic plantings. Ageratum can also be found in several shades of pink, purple, and white. No matter the color, all of these blooms are very popular with pollinators. Butterflies enjoy visiting these plants and drinking their sweet nectar. Ageratum "bury their dead," which means they are so floriferous and fast growing that there is no need to deadhead spent blooms—the plant will quickly grow past it and take care of itself. How convenient!
Ageratum Care Must-Knows
Very often, you can find these tough little plants at your local garden center in multi-packs around springtime. If you're the type that likes to DIY, you can also start these plants in your house before the first frost-free day (see our Spring Frost Garden Zone Map for more details). Generally, 4 to 6 weeks is plenty of time to establish plants before planting them out. As soon as the frost-free date has passed, plant ageratum outside in well-drained, evenly moist soil. Just don't get too hasty, ageratum are not fans of the cold and a late frost can wipe them out.
Ageratum can also perform well in containers—simply use a well-drained potting soil, preferably with a slow release fertilizer. These plants can be heavy feeders and will benefit from the extra food. You can also feed them regularly throughout the growing season with a general-purpose fertilizer, whether they are in ground or in pots. Ageratum will usually let you know when they need more food—they are quick to sport yellow leaves when they're hungry. Design a tall planter using ageratum.
Ageratum can be grown in full sun or part shade, but keep in mind that if you grow your plant in the shade, you might miss out on a few extra blooms and the plant habit may become a little looser. Without full sun, plants may also have more issues with foliar diseases, such as powdery mildew. Powdery mildew is most common during wet, humid weather. Luckily, this won't kill your plants—it's more unsightly than anything. The best course of action is to keep plants dry and to water at the base while making sure they have proper air circulation.
Related: Annual Care Guide
More Varieties of Ageratum
Artist Purple Ageratum
Rich purple blooms cover these small mounding plants, and have good heat tolerance.
'Blue Danube' Ageratum
Ageratum 'Blue Danube' bears lavender-blue flowers and grows only 8 inches tall.
Ageratum Companion Plants
There are few gardens that don't have at least one salvia growing in them. Whether you have sun or shade, a dry garden or lots of rainfall, there's an annual salvia that you'll find indispensable. All attract hummingbirds, especially the red ones, and are great picks for hot, dry sites where you want tons of color all season. Most salvias don't like cool weather, so plant them outdoors after all danger of frost has passed.
Just as you'd expect from something called French, these marigolds are the fancy ones. French marigolds tend to be frilly and some boast a distinctive "crested eye." They grow roughly 8–12 inches high with a chic, neat, little growth habit, and elegant dark green foliage. They do best in full sun with moist, well-drained soil and will flower all summer long. They may reseed, coming back year after year in spots where they're happy.
You've gotta love annual vinca—it really delivers. It will tolerate a wide variety of conditions and still keep blooming with almost unreal-looking, glossy green flowers and pretty pink, lavender, or red flowers that look like tiny parasols. Whether the summer is dry or wet, hot or cold, vinca plugs along unfazed. It makes a great container plant, or plant it in a bed or border, grouping at least eight or more together for best effect. Plant established seedlings in spring after all danger of frost has passed. Vinca withstands drought but does best with moderate moisture. Fertilize occasionally. Like impatiens, this plant tends to be "self-cleaning" and needs little deadheading.