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Floss Flower: Grow & Care for Ageratum Houstonianum

Written by Iris

Jul 31 2021

Floss Flower: Grow & Care for Ageratum Houstonianum
Floss Flower (Ageratum Houstonianum) is an annual herb with no obvious taproot, upright stems, no branches, and propagates by seeds. Flamingo Flower (Anthurium) is native to Mexico and adjacent areas. There are many cultivated horticultural varieties. Currently, it is widely distributed in Africa, Asia (India, Laos, Cambodia, Vietnam, etc.), and Europe. The herb prefers a warm and sunny environment and flowers and fruits all year round.

How to Grow Floss Flower (Ageratum Houstonianum)

Steps for Floss Flower (Ageratum Houstonianum) Propagation with Seeds

Start floss flower seeds indoors about 6 to 8 weeks before the last frost. Germination takes 7 to 21 days on average.
Take your young plants outside after all the danger of frost passes. Transplant after last frost.
After the risk of frost is over, you can plant directly outdoors although the bloom time will be shorter. Aim for a pH of 6.0 to 7.0 during germination.
Plant these annuals under 12″ inches in a sunny to light shaded area of the garden in moist, well-drained soil. Ageratum is not choosy about soil conditions but does not do well in soggy conditions.
For improved health and growth of Ageratum, add 4″ to 6″ inches of organic compost to the planting location. Using a garden tiller incorporate the compost into the soil. The compost helps improve the soil fertility.
Floss Flower

How to Care for Floss Flower (Ageratum Houstonianum)

Light

Ageratum can be grown in full sun or part shade, but keep in mind that if you grow your plant in the shade, you might miss out on a few extra blooms and the plant habit may become a little looser. Without full sun, plants may also have more issues with foliar diseases, such as powdery mildew. Powdery mildew is most common during wet, humid weather.

Soil

Plant ageratum in well-drained but moist soil that has been amended with compost. It is not fussy about soil pH, which increases this annual's versatility.

Water

New plantings should be watered daily for a couple of weeks. After that, depending on the weather and soil type, watering can be adjusted to every two or three days. Clay soils hold moisture longer than sandy soils, so expect to water more frequently in sandy settings.
Different plants have different water needs. Some plants prefer staying on the dry side, others like to be consistently moist. Refer to the plant label to check a plant’s specific requirements.
Ideally water should only be applied to the root zone - an area roughly 6-12” (15-30cm) from the base of the plant, not the entire plant. A soaker hose is a great investment for keeping plants healthy and reducing water lost through evaporation. Hand watering using a watering wand with a sprinkler head attached is also a good way to control watering. If the garden area is large, and a sprinkler is necessary, try to water in the morning so that plant foliage has time to dry through the day. Moist foliage encourages disease and mold that can weaken or damage plants.
To check for soil moisture use your finger or a small trowel to dig in and examine the soil. If the first 2-4” (5-10cm) of soil is dry, it is time to water.
Floss Flower

Temperature and Humidity

These plants are native to Mexico and Central America and will do best in warm conditions. Avoid the temptation to plant them too early in the season, as they may remain stunted for the entire growing season. Humid conditions may make ageratums susceptible to fungal problems; make sure the plants have good air circulation.

Fertilizer

Houseplants may be fertilized with:
  • water-soluble, quick release fertilizers
  • temperature controlled slow-release fertilizers
  • organic fertilizers such as fish emulsion.
Water soluble fertilizers are used every two weeks or per label instructions. Controlled, slow-release fertilizers are carefully worked into the soil usually only once during the growing season or per label directions. For organic fertilizers, such as fish emulsion, follow label directions. Allow houseplants to 'rest' during the winter months; stop fertilizing in late October and resume feeding in late February.

Pruning

While most will require deadheading to encourage new flowers, others like the Artist series will grow up over the spent blooms, covering them up, and may not need deadheading to look good. Cut back if plants start looking tired or are outgrowing the space; they should rebloom within a week or two.

Pests and Diseases

Ageratum is generally hardy when cared for properly. There are a few pests to look out for, though. The largest-sized pest for ageratum is deer. If your plant disappears overnight, a deer is probably the culprit.
Whiteflies may weaken your plant, causing the leaves to yellow. The flies can be lured away from your ageratum with an old- fashioned fly trap. Paint a post bright yellow and cover it with honey or some other sticky substance.
If you notice your ageratum leaves are severely yellowed, wilted, and dying, or if there are lesions on the stems, your plant has probably succumbed to a bacterial infection. The unhealthy plant should be removed to avoid spread of the disease to neighboring ageratums.
You may find brown spots on the leaves or mold on the stems and flowers of your ageratum. The plant will probably survive this problem through the season. However, you may try thinning your plants to allow more air flow around the plant. Sunlight will keep the leaves and flowers drier, too, which will help deter molds from further damaging your plant.
Floss Flower

Varieties of Floss Flower (Ageratum Houstonianum)

There are many varieties of ageratum, with new cultivars regularly introduced. Consider these favorites:
 'Blue Horizon' is a taller blue variety, growing to 2 feet.
'Hawaiian Royal' is a traditional compact series that is known for having genuine blue flowers.
'Red Top' is a tall-growing variety with burgundy flowers.
'Southern Cross' is a compact form of ageratum with bi-colored flowers.
'Blue Danube' is an early blooming, 6- to 7-inch plant with icy blue-purple flowers.
'Red Flint' is an unusual red variety that grows 24 inches tall.
'Dondo White' is a white-flowering variety that grows to 24 inches.
Floss Flower

Floss Flower (Ageratum Houstonianum) FAQ

Does floss flower spread?

The Floss Flower (Ageratum Houstonianum) originated in Mexico and much of Central America but has since spread worldwide. It is a warm-season annual hailing from the Asteraceae family that resembles regular asters but lack ray flowers.

Are Floss Flower (Ageratum Houstonianum) poisonous?

However, all parts of Floss Flower (Ageratum Houstonianum) are poisonous if ingested, so site ageratum carefully if you have small children and pets around.