Plant Type
Sunlight Amount
ageratum blooms in purple container
Credit: Tom McWilliam
ageratum blooms in purple container

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.

genus name
  • Ageratum houstonianum
  • Part Sun
  • Sun
plant type
  • 6 to 12 inches
  • 1 to 3 feet
  • 6-18 inches wide, depending on variety
flower color
foliage color
season features
special features
  • 9
  • 10

Colorful Combinations

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.

More Varieties of Ageratum

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