Ageratum Plant Care

WOW, look at the color of those flowers. Don’t you agree it will brighten up any bedding plants or flower beds in your garden, right?

Yes, it will, as those fluffy blue flowers make rock gardens look fabulous. So, where can you find this bedding plant, and under which name can you find it?

If you stay awhile longer, we promise we will give you all the inside detail to find this outdoor plant.

What is the Ageratum Plant?


The Ageratum flower is part of the Aster family and is more of an annual than a perennial plant. You find it native to Mexico and grown in many North American gardens. When grown in Central America, the people refer to it as the Mexican paintbrush, floss flower, and pussyfoot. But it also goes by the name Ageratum houstonianum.

You can also find the annual plant with different shades of color in bloom time with purplish-blue flowers while others have white flowers. Ageratum blooms in late spring to the first frost. Many gardeners use them as edging plants.

You can grow them in rocks or even in outdoor containers. The floss flower grows up to 30 inches tall.

Ageratum Bedding Plants Care

Ageratum Plant Care

The Ageratum is a prize plant as it grows in the USDA hardiness zones two to eleven. It is annual and only lasts a season needing rich, well-draining soil. You can grow your lavenderblue flowers from seed indoors to sow in the ground after the last frost.

Or, you can buy one available in a container and treat them as an indoor plant near a sunny window or you can place it on the patio.

Potting Mix for Floss Flowers in Flower Beds

Ageratum potting mix

With the profuse blooming of the Ageratum houstonianum, it needs well-drained soil rich in organic matter. We recommend that the acidity level should not be too high, over 7.0 pH, as it will result in seedlings dying.

It helps to avoid using sandy soil as it can make your plant chlorotic. Still growing them outside, they are generally hardy. If grown indoors to transplant outdoors, we recommend a space between them up to ten inches apart.

The hole needs to be big enough for the root ball to spread its roots. You can also apply a two-inch layer of mulch to keep the soil moist and protect the root system.

Lighting Needs of Ageratum Plants

Ageratum plant lighting requirement

The floss flower needs good air circulation and can grow in partial shade when it comes to the floss flower. But your Blue Ageratum grows best in full sun. Keeping them in too much shade reduces the blooms and legginess while the flower color fades. What your small mounding plants are sensitive to is frost.

Watering Needs for Your Plants

Okay, to prevent root rot leading to an unhealthy plant, your Ageratum houstonianum needs moderate watering. The reason is that the plant habit is to grow shallow roots. Therefore, regular watering helps boost growth and can prevent wilting in warmer regions.

Your floss flower does not do well in dry places, and soil moisture is essential to prevent them from wilting fast. Still, your Ageratum floss prefers warmth, and you can water them with warmer water instead of cold grown indoors.

Doing this is vital for young plants as the warm water helps to speed up their growth. It helps to keep the soil moist throughout spring and summer but never overwaters them.

Fertilizing Floss Flower

fertilizing Ageratum

Okay, compared to other plants, the Ageratum floss needs regular feeding. We recommend a slow-release granular fertilizer applied when planted and in the mid-season. Or, you can feed your flowers every two weeks with a water-soluble liquid fertilizer.

Temperature and Humidity

As the floss flower thrives in the soil conditions of Mexico, they prefer warm climates. We recommend avoiding the temptation to plant them too early in the growing season. Furthermore, humid climates make the plant susceptible to different fungal problems, and air circulation is essential.

Grooming Ageratum Houstonianum

Okay, now you may think this fast-spreading ornamental plant means it has low maintenance. Wrong, as it needs more caring than your other garden plants. Your taller varieties need support, and the spent blooms need removing.

So, you can deadhead spent flowers by removing them with your fingers. But a note of warning is to be extra careful with the seeds during the bloom time as they can spread fast, taking over your garden.

Your plant does not need much pruning, but you can trim them back when wearing out or spreading too fast. These plants can thrive in full sun with afternoon shade but die off at the first frost.

Propagating Ageratum Plant

Before the last frost date, you can sow the seeds indoors in containers, and the germination takes up to 21 days. Then, you can spread the seeds over a tray filled with a seed starter and cover them by sprinkling the soil over them.

Your seeds will need light to germinate, and a warm sunny location will do with frequent misting of water. Once they sprout, you can thin them out to once per cell in the tray. After all dangers of frost have passed, you can transplant your young plants outdoors, but the bloom time will be shorter.

Ageratum Varieties

You can find many varieties of Ageratum to grow in the garden or containers. With the bi-colored flowers, you can mix and match them, and they look great in flower arrangements.

Artist Purple Ageratum

Artist Purple Ageratum

The flowers have a rich purple shade and are a small mounding plant that can tolerate heat well.

‘Blue Danube’ Ageratum

'Blue Danube' Ageratum

The Ageratum flower has lavender-blue blooms and only grows up to eight inches tall.

‘Hawaii White’ Ageratum

'Hawaii White' Ageratum

Compared to the other dwarf varieties with their vibrant colors, this one blooms white flowers with a height up to eight inches tall.

Ageratum Diseases & Pests

Ageratum plant disease

Generally, the floss flower is hardy, but you still need to look for pests and diseases. But the good news is that both are treatable. If you notice powdery mildew, it can be from root rotting or Botrytis as it attacks the soil moisture

Pests that can bother your plant Ageratum are fungus gnats, plant lice, aphids, spider mites, whiteflies, and thrips. To lure away whiteflies you can use the old-fashioned fly trap.

Frequently Asked Questions

The Ageratum growth varies as some can grow up to six inches while others grow ten inches tall. Hence, it all depends on the species you have.

The floss flower can bloom from spring throughout summer to fall, depending on where you live.

Your plant might be infected by spider mites resulting from warm, dry weather. In most cases, the older flowers turn brown and remain on the plant, while other varieties are self-cleaning.

The good news is that you can buy the floss flower at a local garden center or find them online. But we are so happy to let you know that you can purchase the seeds right here at Plantly.

Whether you want to buy, sell or simply reach out to other plant enthusiasts, Plantly is the right place to be!

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