How to Grow and Care For Ageratum (Floss Flower)

How to Grow and Care For Ageratum (Floss Flower)

How to Grow and Care For Ageratum (Floss Flower)

Image by Hans from Pixabay

Growing blue flowers in the garden can occasionally be challenging. There are few options, and the majority need a site with full sun. Even in partially shaded gardens, ageratum plants’ fluffy blue blossoms bring the desired blue tint. Ageratum maintenance is basic and straightforward, especially for novice gardeners. The ageratum flower that is most frequently seen in gardens is a hybrid, and it grows in a small, compact form. You will always have a blue flower alternative for the bed or border after you understand how to plant ageratum and nurture it properly.

This member of the Aster family, sometimes known as floss flower, is a group of 40 species of annuals, perennials, and shrubs that are indigenous to tropical and subtropical areas of North and South America. The ornamental varieties of billygoat weed (Ageratum conyzoides) that are available to home gardeners are grown as annuals and are attractive to butterflies, hummingbirds, and insect pollinators. Billygoat weed (Ageratum conyzoides), which has herbal and medicinal qualities, is highly invasive, mostly in Africa, but can also be found growing wild in parts of the Southern US.

Botanical Name Ageratum houstonianum
Common Name Ageratum, floss flower
Plant Type Annual
Season of Interest Spring (Late), Summer (Early,Mid,Late), Fall
Spacing 12″ (30cm)
Water Needs Average
Maintenance Low
Soil Drainage Moist but Well-Drained
Mature Size 6-30 inches tall, 6-18 inches wide at maturity
Sun Exposure Includes both full sun and partial shade.
Soil Type Moist, well-drained soil (Chalk, Clay, Loam, Sand)
Soil pH Ranges from 6.0 to 7.5. (slightly acidic to slightly alkaline)
Bloom Time June through first frost
Characteristics Showy, Cut Flowers, Plant of Merit
Tolerance Deer, Rabbit
Attracts Butterflies
Flower Color Purplish blue; pink and white cultivars also available
Hardiness Zones 2–11 (grown as a true annual)
Native Area Mexico

Ageratum Varieties

The following cultivars of ageratum flowers are common variants that come in a variety of blue hues: 

Hawaii” – This variety boasts royal blue blooms. One of the longest-lasting of the genus, it blooms early.

Blue Mink‘ – This cultivar grows to a height of 12 inches (30 cm) and has powder blue blooms. 

Blue Danube‘ – A selection with medium-blue blooms that only grows 6 to 8 inches (15–20 cm) tall.

Hawaiian Royal” is a classic compact series that is renowned for its indelible blue blossoms.

Red Top‘ is a tall-growing cultivar with crimson flowers.

Southern Cross‘ is a small ageratum with bi-colored flowers.

Red Flint‘ is a rare red cultivar that matures to a height of 24 inches.

Dondo White‘ is a white-flowered cultivar that matures to a height of 24 inches.

When to plant

Late spring to early summer, after all threat of frost has passed, is when plant nurseries begin operating outdoors. 8 to 10 weeks prior to your final average frost date, sow seeds inside. After your typical last frost date, you can put seeds outside, but plants won’t blossom until late summer or fall. Ageratums are heat-loving plants that cannot survive in extreme cold.

Where to plant

In a bed or container that has rich, permeable soil that will retain an even level of moisture.

How to plant

Tiny ageratum seeds should be carefully pressed into the surface of moist seed starting mix before being sown. Ageratum seedlings are typically purchased by gardeners, although only the dwarf types are frequently found as bedding plants. Allow 12 inches (30 cm) between very tall varieties and keep dwarf varieties 8 inches (20 cm) apart in all directions.

Potting and Repotting

Ageratum is a good plant to include in window boxes, hanging baskets, or mixed patio containers. It thrives in any commercial potting mix with good drainage.

Image by Jacques GAIMARD from Pixabay

Ageratum Care


Give ageratums full sun in cold climates. The plant can benefit from afternoon shade in the South.


Ageratum thrives in well-drained, moist soil that has been amended with compost. It is not picky about soil pH, which adds to its adaptability.


Ageratums can quickly dry out and wilt because of their shallow roots. Water should be provided consistently on a weekly basis, or more frequently during warm spells. Watering early in the day, when plants can dry out, or watering the plants’ bases rather than their tops will help prevent foliar diseases.

Temperature and Humidity

These plants, which are indigenous to Mexico and Central America, thrive in warm environments. To avoid them remaining stunted throughout the entire growing season, resist the urge to plant them too early in the year. Ageratums may be more susceptible to fungus issues in humid environments, so make sure the plants have good air circulation.


When grown in healthy, rich soil, ageratums don’t need much feeding, but if the leaves start to turn yellow, they need nutrients. The plants should regain their health and begin to bloom profusely when granular slow-release balanced fertiliser is incorporated into the soil surrounding them.

Diseases and pests

Ageratums are generally pest- and disease-resistant when grown in the right location. Fungal diseases like powdery mildew can be brought on by excessive shade, poor air circulation, or high humidity. Root rot may be caused by inadequate drainage or overwatering. Aphids, whiteflies, and spider mites are a few potential insect issues.


Pinching back the growing tips will encourage the plants to spread and fill out when they are young. Deadheading the spent flowers will encourage further growth and blooms, though it is not necessary. When the first sign of frost appears, these plants will begin to wither and should be removed from the garden.

How To Select The Appropriate Ageratum

Here are some ideas to take into account when selecting a form:

For borders and beds
Taller varieties can be arranged with other annuals and perennials in the middle of a border. The front of a bed or mixed border can be planted with shorter types.

For edging
Along paths, shorter varieties are best.

For containers
Low growers should be planted with other annuals that have similar requirements, like petunias, coleus, or pelargonium.

Regarding bouquets, floral designs, and cutting gardens
For cutting, choose plants with tall stems.