Ageratum

( aj - err - AH - tum )

At-A-Glance Information

Commonly referred to as Floss Flower, Whiteweed, Mexican Painbrush, Pussy Foot, Blueweed or Bluemink, this annual enjoys full sun in cooler climates, partial shade to shade in warm ones. These flowers need regular water and are native to Central America and the West Indies. They are easy to grow and dependable additions to the garden. Leaves are soft green and round, and dense flower clusters resemble powder puffs, attracting butterflies and other pollinators to the garden. Use Ageratum in mixed beds and borders, in containers, or in cut flowering gardens. They can also make great plants for hanging baskets. Take care when planting Ageratum in the landscape, as plant parts are toxic to cattle, pets and humans if ingested. Certain species are also considered invasive in some areas.

Ageratum Species and Varietals

The genus Ageratum includes 40-60 distinct species and is a member of the plant family Asteraceae. Floss Flower grows in USDA hardiness zones 2-11 or Sunset growing zones 1-24, and the genus is named for the Scottish physician who first collected and documented the plants, William Houston. The genus Ageratum gets its namesake from the Greek word 'ageras' which means non-aging, referring to the long-lasting blooms. There are many sub-species that vary in size, flower color, and habit. See the descriptions below for more information. To find your zone, click here: Zone Map.

Ageratum conyzoides (Ageratum microcarpum) (Billygoat-Weed, Chick Weed, Goatweed, Whiteweed, Mentrasto, Cut Lon)
This species is native to tropical areas of South America, mainly Brazil, and is considered an invasive weed in many places around the world, including Africa, Australia, Southeast Asia, Hawaii, and mainland United States. These flowers grow well in USDA hardiness zones 8-11 as a perennial, but can be grown in any zone as an annual.

Ageratum houstonianum (Floss Flower, Bluemink, Goatweed, Blueweed, Pussy Foot, Mexican Paintbrush)
This species is commonly used as a garden ornamental, and forms an annual herbaceous plant that blooms from spring through fall. They reach 1-3 feet tall when mature and in bloom, and are native to Central America (mainly Guatemala and Belize). These plants are considered invasive in the United States, Australia, Europe, Africa, China, Japan, New Zealand, and the Philippines. Cultivars are listed below:

'Blue Blazer'
4-6 inches tall.

'Blue Danube'
4-6 inches tall.

'Blue Surf'
4-6 inches tall.

'Royal Delft'
4-6 inches tall.

'Blue Mink'
9-12 inches tall.

'North Sea'
9-12 inches tall.

'Capri'
12 inches tall.

'Southern Cross'
12 inches tall.

'Blue Horizon'
2.5 feet tall, great as a mid-border plant and for cutting for arrangements.

'Swing Pink'
Bright pink flowers, grows 6-8 inches tall.

'Red Top'
Deep pink flowers, grows to 2.5 feet tall.

'Summer Snow'
White blooms on a 9-inch tall plant.

Caring for Ageratum

Take care when planting Ageratum in the landscape, as plant parts are toxic to cattle, pets and humans if ingested. Ageratum plants are typically purchased as starts from a reputable nursery, but they can also be grown from seed. Make sure to wait until the last frost of the year has passed by before planting, as cool temperatures can take out young or recently installed plants. Choose a space in the landscape that receives full sun to partial shade. Ideally, they should get between 6 and 8 hours of sun each day but they do appreciate some shade in warmer climates. Plants should be spaced 6-8 inches apart for best coverage and airflow. Ensure that soil is well-draining, rich in nutrients, and has a pH of between 6.0 and 7.5 (slightly acidic to neutral). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water new plantings regularly as they establish a strong root system in their new home.

As long as soil is fertile before planting, these flowers will not need any additional fertilizers during the growing season. If these flowers seem to be struggling and are not blooming or growing well, fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. Prune during the growing season to remove dead, damaged or diseased foliage or stems and to deadhead spent flowers. If you will be collecting seeds for propagation, make sure to leave some flowering heads on plants to mature. Ageratums are typically grown as annuals, and at the end of the growing season once cooler temperatures set in, they can be removed. New plants can be installed the next spring after the danger of frost has passed.

Harvesting Ageratum
Ageratum, or Floss Flower, is widely used as a cut flower to add whimsy, mass, texture and color to mixed bouquets. Foliage is also used to add greenery to bouquets and fresh arrangements. To harvest cut flowers, make sure to cultivate a variety that has longer stems than the normal, short garden ornamentals. Good varieties that grow to be at least 24 inches tall include 'Timeless Mix', 'Tall Blue Planet', and 'White Bouquet'. For the largest harvest, make sure to succession sow seeds every 2-3 weeks for 6 weeks once temperatures warm in spring, and thin to space plants between 9 and 12 inches apart for best airflow. Harvest when flowers are 3/4 of the way open, making cuts at the base of stems with sharp, clean garden shears or snips. The best time to harvest Ageratum flowers is in the morning, after the dew dries from leaves but before the heat of the day sets in. Drop cut stems in cool water immediately. Ageratum flowers have a vase life of between 5 and 10 days.

Propagation

Before trying this method, keep in mind that propagation of Ageratum by seed does not ensure that you will end up with the exact same plant as you harvested the seed from. If you are looking for an exact clone, it is best to simply purchase another of the same species from a reputable nursery. To complete this propagation method, you will need to allow your flowers to stay on the plant long enough to come to seed, so do not completely deadhead all of your blooms. Seeds will be mature and ready to harvest in late summer or early fall, when the flowers have dried and turn brownish. Cut the flower heads off of your plant at this time, and take the seeds out of their pods. For pictures of the dried flowers and seeds, see the images below. To grow Ageratum from seed, follow these directions:

Gather your materials. You will need a pot or seed tray, potting soil that is well-draining, and a spray bottle filled with water.
Seeds can be sown in place or started indoors in the late wintertime (6-10 weeks before the last frost date) and then transplanted outside. Prepare your pot or growing tray by filling it with potting medium.
Place your seeds on top of the potting mix, spaced about 4- 6 inches apart. Sprinkle potting medium over the top until the seeds are covered. As the seeds are starting out, it is best to use a spray bottle to add moisture to avoid uncovering their soil topping or dislodging them; they are very small. Keep the soil moist as the seeds develop, using a seed tray cover or plastic to cover your pot to keep moisture in and humidity high.
Continue to monitor for moisture and adequate soil covering until the seeds start to sprout, which should take between 7-21 days. Once the chance of frost has passed by, seedlings can be transplanted to a sunny area of the garden. Keep the soil moist as the plant develops.

Ageratum seed pods dry out and turn brown when seeds are mature.

Ageratum seeds are very small, and look like this.

Problems and Pests

Some species of Ageratum, including Ageratum houstonianum and Ageratum conyzoides, are considered environmental weeds when grown outside of their native range. Check with local authorities before planting. Ageratum flowers have few issues in the landscape, but can sometimes be susceptible to developing problems with the following pests and diseases: