Ageratum is a classic garden annual and one of the best annuals for cutting. Sometimes called a floss flower, it has playful, small blooms that resemble tiny pom-poms covered with floss-like filaments. It also offers a rare color in the flower world: blue, perfect for patriotic plantings. Ageratum can also be found in several shades of pink, purple, and white.

No matter the color, these blooms are very popular with pollinators. Butterflies enjoy visiting these plants and drinking their sweet nectar. The plants begin to bloom in late spring and keep the show going until the first frost. These rugged plants can withstand poor soil conditions and aren't a favorite for deer.

Where to Plant Ageratum

Ageratum can be planted in any spot with fertile, well-draining soil with a pH on the acidic side (5.0 to 6.0), where they get full sun for at least part of the day. If you live where summers get hot, a location in partial shade and sheltered from the afternoon sun is acceptable. However, ageratum should be planted in full sun in more northern locations. 

The pompom-shaped flowers are eye-catchers in flower beds, borders, and rock gardens, as well as in pots, mixed containers with other plants, and hanging baskets. The effect of the blue color is even more stunning in mass plantings, but they are also wonderful companion plants to annuals in other complementary colors, such as salvia.

How and When to Plant Ageratum

 Plant ageratum after the last frost date. The young plants should be hardened off before planting them outside.

Ageratum roots are shallow, so you don’t need to dig a hole much deeper than the pot the seedling comes in. Space them 9 to 12 inches apart. Planting them too close together will lead to poor air circulation and can encourage the spread of disease.

Ageratum Care Tips 

Light

Ageratum can be grown in full sun or part shade, but keep in mind that with less sun exposure, the bloom might be less prolific, and the plant might become less compact and leggier.

Soil and Water

Ageratum should be planted in fertile soil with good drainage. Water the plants regularly until they are established. The plants need about 1 inch of water per week, so if it does not rain, you will need to water them. Container plants require more frequent watering—daily in hot summer weather. 

Temperature and Humidity

Ageratums are warm-season annuals; cold is their enemy. If they are planted too early in the spring and a cold spell hits, they can be easily wiped out. However, if you get early frosts at the end of the summer, you can extend their lifespan by covering the plants. 

Fertilizer

Their extended bloom makes ageratums heavy feeders. Fertilize in-ground or potted plants with a general-purpose fertilizer about once a month throughout the growing season. The plants will usually let you know when they need more food—they are quick to develop yellow leaves when they lack nutrients.

Pruning

Ageratums are so floriferous and fast-growing that there is no need to deadhead spent blooms. The plant will quickly overgrow them, which is one of the reasons it is considered a low-maintenance annual.

Potting and Repotting Ageratum

With their compact size, the plants also make excellent container plants. Use a well-draining potting soil and feed them with a slow-release fertilizer. 

Pests and Problems 

When grown in a shady spot, plants may 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 is primarily unsightly. The best course of action is to keep plants dry and water at the base while ensuring they have proper air circulation.

How to Propagate Ageratum

Garden centers sell these tough little plants in multi-packs in the spring, but you can also grow them from seed.

• Start argeratum indoors 4 to 6 weeks before the first frost-free day.
• Do not cover the seeds with soil, as they need light to germinate.
• When the seedlings are large enough to remove, plant them in individual seed pots.
• Harden off sturdy plants with several sets of true leaves before transplanting them to the soil.
• As soon as the last frost date has passed, plant them outside.

Types of Ageratum

Artist Purple Ageratum

Rich purple blooms cover these small mounding plants with good heat tolerance.

'Blue Danube' Ageratum

Ageratum 'Blue Danube' bears lavender-blue flowers and grows only 8 inches tall.

'Hawaii White' Ageratum

Ageratum 'Hawaii White' grows 6-8 inches tall and has white flowers.

Ageratum Companion Plants

Salvia, Sage

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.

French Marigold

Just as you'd expect from something called French, these marigolds are the fancy ones. French marigolds are frilly; 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, returning year after year in spots where they're happy.

Annual Vinca

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. This plant tends to be "self-cleaning" and needs little deadheading.

Garden Plans for Ageratum

Blue-Theme Garden Plan

Create a soothing, all-blue garden in a partly shaded spot with this garden plan.

English-Style Front-Yard Garden Plan

Give your home a welcoming feel with an exuberant cottage garden in the front yard.