Floss flower: location, care & winter hardiness

Due to the persistent flowering floss flower is beautiful to look at for a very long time. Especially as a bedding, border and balcony plant, it is used with pleasure and often.

Floss flower (Ageratum houstonianum) offers a colourful variety of cultivars – but it scores rather less with its winter hardiness. In this article you will learn everything important about the ideal location and care of floss flower. Also about the winter hardiness and some varieties you can find detailed information below.

Floss flower: characteristics and origin

The name Bluemink is used as a synonym for the poisonous Compositae (Asteraceae). The plant originated in Central America and parts of the Caribbean islands. Meanwhile, due to its use in the garden, floss flower is also found feral in the subtropics, tropics, as well as rarely in temperate zones. Natural habitats of the plant include shrubberies, forest edges, pastures and clearings with fresh to moist soils. Actually, Bluemink would have the potential to grow into a woody perennial or semi-shrub at the base but in Central Europe it is mainly cultivated as an annual due to its lack of winter hardiness. Floss flower is still a suitable plant for pots and balcony boxes, and in this case, even frost-free wintering can be provided.

The growth habit of floss flower is compact, bushy and densely branched. It reaches heights between 15 cm and 60 cm. The plant bears heart-shaped leaves with notched edges and downy pubescence. The unusual flowers of floss flower appear in shades from light blue to violet-blue, purple and white. They sit in dense, umbellate flowerheads and consist of tubular as well as ray florets. The blooming period of Ageratum houstonianum can extend from late May into November.

Is floss flower bee friendly? The nectar and pollen supply of the plant is not high but because of the extremely long flowering period of floss flower, it is quite important for bees.

The most beautiful varieties

The many floss flower varieties differ mainly in growth height and flower colour. Below we have listed some of the most beautiful varieties:

• Ageratum houstonianum ˈBlue Horizonˈ: The growth habit of the cultivar ˈBlue Horizonˈ is compact. It grows between 40 and 60 cm high and bears violet-blue flowers.

• Ageratum houstonianum ˈBasso Purpleˈ: This variety is adorned by purple flowers and grows up to 45 cm high.
• Ageratum houstonianum ˈBlue Planet F1ˈ: This hybrid is a very good cut flower that reaches stem lengths of about 80 cm. It proves itself due to its productivity and excellent durability.
• Ageratum houstonianum ˈWhite cutˈ: This floss flower variety bears white flowers and grows up to circa 60 cm tall.

• Ageratum houstonianum ˈCapriˈ: The flowers of this variety are deep sky blue. The growth is compact, spherical and the height is between 20 and 30 cm.
• Ageratum houstonianum ˈPink Ballˈ: The varietyˈPink Ballˈ blooms in a beautiful old pink to intense pink and remains quite low with a height of 15 to 25 cm.

Tip: The tall varieties of floss flower are particularly suitable as cut flowers. For a long shelf life not yet fully opened flowers are cut off early in the morning.

Planting floss flower: location and method

Floss flower should be planted outdoors no earlier than mid-May as damage may otherwise occur due to late frosts. The ideal location for floss flower should be in a sunny position on permanently fresh to moist, sandy and humous-rich soil, which tends to be low in nitrogen to moderately nutritious. Semi-shaded places can also tolerate the composite but sufficient light is important for flowering. Floss flower forms many flowers especially with the onset of long days and at temperatures between 17 and 20 °C.
Since the plant is susceptible to mildew in the morning humidity, we recommend a location, which is already reached by the sun in the morning.

Tips for use: Floss flower is excellent in group plantings or as an accompaniment to taller flowering plants. Therefore, if arranging in small groups, a planting distance of 40 cm should be maintained.

To grow in balcony boxes or pots, use high-quality soil for filling that can retain water well. For this purpose, for example, our peat-free Plantura Organic All Purpose Compost is suitable, which, with the coconut fibres and quality compost it contains, has the water-holding capacity that the floss flower needs. It also fully covers the moderate nutrient needs of the plant for the time being. The pots or boxes should in any case provide a drainage for excess watering and ideally at the bottom is still filled with a layer of expanded clay about 3 cm high. If you want to grow your own floss flower from seed, you can simply follow our instructions below.

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Sowing of the floss flower:

• Pre-culture indoors in February/March.
• Sow directly outdoors from mid-May onwards.
• Fill a sowing tray with substrate.
• Place seeds in trays and press only lightly, as it is a light germinator.
• The substrate should always be kept moist.
• Germination temperature: approx. 20 – 22 °C.
• Germination period: 10 – 14 days.
• After 3 – 4 weeks, transplant 3 seedlings each into a pot.
• To harden, do not place outside in direct sunlight on warm days.
• Plant out after the last signs of frost.

Is floss flower eaten by snails? Unfortunately, floss flower is a favourite meal of snails. Therefore, it may also be useful to make the planting distance a little more generous, so that the snails are not offered a hiding place. You can discover how to combat snails in our dedicated article.

Care

Mainly because of its medium to high water requirements, floss flower is not necessarily the easiest plant to care for. Since it prefers sunny locations but needs fresh to moist soil, that means lots of extra watering in hot summers. Under drought floss flower vitality suffers significantly. Under such circumstances, the crop is also susceptible to spider mites (Tetranychidae). For planting in containers, this means more effort: on hot days, watering twice a day may be necessary – the substrate should always be at least fresh.

Since the composite plant likes to stand on rather nitrogen-poor to moderately nutritious soils, fertilisation should not be too generous. In addition, too much nitrogen supply can result in increased foliage growth and fewer flower starts. A floss flower in fresh potting soil such as our Plantura Organic All Purpose Compost does not require additional fertilisation.
When planting in the bed, a slow-release granulated fertiliser such as our Plantura Flower Food is ideal. After this has been superficially incorporated, it gently and slowly releases its nutrients over several months. When planting in the garden bed in mid-May, the fertiliser can be applied directly with it. From the end of May, there should be no fertilisation or only greatly reduced fertilisation, so as not to disturb the induction of flowering. In the case of perennial culture of floss flower, a single fertilisation annually in May is quite sufficient.

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If you want to stimulate your floss flower to bloom by additional measures, then you should always remove the parts of the plant that have bloomed off. Propagation of floss flower works most easily by sowing. It should be noted that some varieties in the market are F1 hybrids, which do not produce true variety seed.

Is floss flower hardy?

The floss flower is not hardy and is therefore mainly traded as an annual plant but it is quite possible to overwinter floss flower. This is especially convenient if the plants are cultivated in pots or balcony boxes. These then only need to be cut before the first frosts and put in a bright place, cool between 5 and 10 °C. In the winter quarters, the composite should not be fertilised and watered a little less but the soil should be kept fresh. From May, the tub can be placed outdoors again and fertilised once with a complete organic fertiliser. However, since floss flower is already naturalised in a few very mild areas of Germany, with a little luck you can still enjoy the plant in the next few years due to seeding or mild winters, without the need for costly overwintering.

Is floss flower toxic?

The floss flower is a poisonous plant that is harmful to humans and animals. If there are small children or pets in the garden, it is better not to use floss flower in the garden. Although Ageratum houstonianum is reported to have high potential for medicinal use, it has not yet been used in this field. A close relative of the plant was sometimes found to have liver-toxic effects in experiments with rats, which its German name rather does not suggest. Because floss flower disrupts hormonal control of insect development, it is being studied as a source of biological control agents – as such, it could be used against various pests and nuisances.