Floss Flower (Ageratum houstonianum)

Floss Flower (Ageratum houstonianum) is cultivated for the beauty of its pompom-shaped flowers that occur mainly in shades of blue. In this article we will cover in detail how to plant Floss Flower (Ageratum houstonianum).

These plants are very popular for flower beds but can also be grown in pots.

Blue is a highly appreciated color in gardening because of its rarity. There are also floss flower varieties that produce white, pink and purple flowers.

They are usually purchased as seedlings in trays or small pots. Still, the most economical way is to grow them from seed as we’ll see in this guide.

Plant profile

Common name: Floss Flower, Bluemink, Blueweed, Pussy foot, Mexican paintbrush
Scientific name: Ageratum houstonianum
Plant type: Annual / Biennial
Height: 10cm - 50cm
Spread: 10cm - 50cm
Foliage: Deciduous
Flower color: Blue, Pink, Purple, White
Season of interest: Autumn, Summer
Sunlight: Full Sun
Soil: Chalk, Clay, Loam, Sand
Moisture: Moist but well drained
Garden type: City & Courtyard Gardens, Informal Garden, Patio & Container Garden
Planting type: Containers & Pots, Cut Flowers, Flower borders and bedding, Hedging & Screens

Ageratum belongs to the Aster family and includes about 40 species of annuals, perennials and shrubs. They are native to the tropical and subtropical regions of North and South America.

Ornamental varieties used in gardening are grown as annuals and attract hummingbirds, butterflies and other pollinating insects.

Characteristics

Floss flowers are tiny in the shape of fluffy little pompoms. They are produced in dense agglomerates in blue, purple, white or pink. The leaves are green and oval in shape.

The growth habit of these plants varies from short and compact to erect and disperse, depending on the growing conditions.

Flowering season

Ageratums flower for a long time, from late spring until the first frosts.

When to sow

Sowing should be done indoors in trays about 8 to 10 weeks before the expected date of the last frost.

Seeds can also be sown directly outdoors after frosts, but there will be no flowers until late summer or autumn.

How to sow Floss flower (Ageratum)

I bought a small packet of Ageratum seeds. First time I tried these annual flowers. I was fascinated by the combination of these flowers in a flowerbed in a public garden and put it on my list for the following year.

When you buy seeds, always confirm that the package is properly sealed or that inside the larger package with the commercial image, it contains an airtight package to properly protect the seeds. Also check the seed collection date and expiration date on the package.

Ageratum seeds are very small and difficult to handle individually. You can mix them with sand to make sowing easier.

Prepare the tray with proper sowing compost and press lightly so that the surface is leveled.

Distribute the seeds evenly (here already imperceptible) on the tray. They don’t need to be covered, the seeds are very small and will germinate quickly.

Slowly place the tray in a tank or container with water so that the moisture is absorbed from the bottom to the top. This way we do not disturb the seeds, unlike what would happen if we watered with a watering can.

Label the tray to identify the seeds.

Cover the seeds in such a way as to maintain moisture in the tray but at the same time allow light to enter.

Germination takes place 8 to 10 days after sowing, with ideal temperature conditions.

Remove cover at this stage depending on weather conditions. Keep the tray sheltered from direct sun and rain.

 

After 6 weeks the small ageratums will be ready to be handled and planted individually. In this case, you can clearly see that I sowed them in excess, the germination rate of these seeds is high.

With the help of a spatula, lift the small plants, loosening the roots and bringing in some soil. This facilitates their adaptation and growth.

Always hold small plants by the leaves. They are very delicate at this stage. We plant in small pots and also individually in trays to develop a little more before planting outside.

When to plant

The planting outdoors can be done as long as the danger of frost has passed, from late spring to early summer.

During tray growth it is important to cut the central shoot when it elongates. In this way the plants will be forced to launch lateral shoots which will form stronger and more compact plants. When frosts have passed and with the small plants already quite robust, they should be planted outside.

Where to plant

Floss flowers are used in front of flower beds, or as small hedges to limit garden paths. They can also be planted in pots.

How to plant ageratum

Gently remove the plant from the tray so as not to disturb the roots too much.

Dig a hole and place it so that the top of the root is level with the surface of the soil.

Gently squeeze the soil around the base and water well.

Soil

Plant floss flower in well-drained soil, rich in organic matter.

Soil pH

Ageratum is very tolerant of soil pH.

Does ageratum need full sun?

Ageratum prefers to be planted in full sun, although it tolerates partial shade.

Plants bloom best in full sun. Too much shade can result in fewer flowers and less compact plants.

Although they appreciate heat, in really hot regions, plants benefit if they get some shade in the afternoon.

How far apart do you plant ageratum?

Taller varieties should be planted 30 centimeters apart. Smaller varieties should be planted 15 centimeters apart.

How long does it take ageratum to bloom?

In late spring or early summer you should start to see the first flowers. Ageratum begins to bloom abundantly from mid-summer. I decided to plant them in front of a flower bed, together with French marigolds (Tagetes).

How do you care for a ageratum plant?

Fertilizers

Ageratum plants are greedy and benefit if they are regularly fed.

Mix a granular slow-release fertilizer into the soil at planting time and reapply mid-season, or use a water-soluble fertilizer twice a month, according to package instructions.

Yellow leaves can be a sign that plants don’t have enough food.

Ageratum also benefits from mulching, as the mulch of organic material conserves soil moisture and releases nutrients as it breaks down.

Do you have to deadhead ageratum?

Removing dead flowers causes the plants to flower again, although this is not entirely necessary in ageratum.

Prune plants in their early growth stages so that they grow compact and produce more flowers.

How much water does a ageratum need?

Ageratum develops shallow roots which make them quickly dry and wither.

Water consistently as needed in your region, especially during hot periods.

To prevent foliar diseases, do not wet the leaves, water in the morning and only the soil at the base of the plants.

Diseases and pests

When planted in ideal conditions, ageratums are resistant to most pests and diseases.

Too much shade, lack of air circulation or excessive humidity can cause fungal diseases such as powdery mildew.

Poor drainage or excessive watering can result in root rot.

Possible problems with insects include aphids and whiteflies.

How to choose the right variety

With different shapes to choose from, here are some tips to consider when choosing the Ageratum variety:

For flowerbeds and borders

Shorter, more compact varieties can be planted in front of a bed or border.

Taller varieties can also be planted in the middle combining with other taller annuals and perennials.

For hedges

More compact varieties are suitable for limiting paths.

For pots

Combine small varieties with other annuals with similar needs such as petunias or pelargoniums.

For bouquets and floral arrangements

Taller varieties with long stems are best suited for use as cut flowers.