The frothy purple blooms dot abandoned fields and pastures across the continent from summer into autumn. The unique color is easily recognized as the floss flower or ageratum. This former native of Central American and Mexico fields has made itself at home throughout most of North America and as far away as Scandinavia, Australia and South Africa (where it is considered an alien invasive.)
This mound-shaped annual is a member of the vast Asteraceae family and it thrives in sunny meadows, unkempt fencerows and the edges of forests and woods. The flowers start to appear in mid summer and continue on until frost. Wind disperses the seeds and a new generation appears each spring.
Plants dot the pastures and fields because grazing animals tend to have enough sense to avoid them, as it is toxic if they ingest it. Amazingly enough, insects avoid eating this plant as well. It produces compounds that trigger molting cycles and even renders some insects sterile that snack on it. Deer even tend to avoid it, however hungry deer are rarely picky if there are no other choices. Rabbits find the taste unpleasant as well. Do use ageratum in butterfly and pollinator gardens, floss flowers are a great nectar source for butterflies, wasps and bees and in late autumn, it is one of the last meals they can find before frost puts everything to bed for the season. This plant is an unexpected splash of an unusual color amid yellows, whites and pinks that makes them an excellent focal point in the garden.
Early peoples used the sap from the stems to treat cuts and wounds and the crushed leaves were rubbed on exposed skin as an early mosquito and biting insect repellent. Modern lab results confirm that the native peoples were on to something and that it is, indeed a good repellent. This knowledge could come in handy for campers and hikers. Essential oil has been shown to have antibacterial properties and modern medicine is even exploring the possibility of using it as a cancer treatment. However, it is important to use any wild plant with caution, as the compounds could interact with any medications you may be taking and there's no way to know about potential allergic reactions as well.
Many garden centers and nurseries offer hybrid selections in early spring. Most of these are more compact than their wild cousins and thrive in the garden border. Plant in a sunny, well-drained location and water regularly until the plants are established. They like regular moisture, but can't stand wet feet, so they are not a good choice for boggy or damp areas. Gardeners can keep the pretty blue or purple flowers producing all season by dead-heading spent blooms, just like any plant from the Asteraceae tribe. (this includes most plants that resemble daisies) There is a wide range of blue shades available in the garden centers, ranging from a royal blue to white or pink, although the paler colors tend to look ragged and worn quicker than the blues. Many of our participating PlantScout vendors offer a choice of either plants or seeds, so there's sure to be one that is right for your garden. The hybrids tend to be less weedy than their wild counterparts and are an excellent choice for smaller gardens. It is even happy as a container dweller and settles happily with grasses and foliage plants that share its preferred living conditions. I've mixed the hybrid cultivars in containers with pentas, Shasta daisies or lantana with good results. They are a bit prone to powdery mildew, so water early in the day so that the foliage has time to dry before evening. In the southern parts of the country a bit of afternoon shade is welcome, but ageratum blooms best with at least 8 hours of sun.
If you choose to start your plants from seed, prepare your flats about 6 weeks before the last frost is expected in the spring. Sow the tiny seeds in damp medium and just barely cover with a fine sprinkle of the potting mix. Place in a warm spot and the little plants should germinate in a week to 10 days. Place under lights, keeping the light source about 2 inches off the leaves. As the plants grow, thin to 1 or 2 per cell and gradually expose them to the outdoors. This is called hardening off. Once all danger of frost is passed, plant out in the garden.
Ageratum houstonianum produces a pop of unexpected interest that will light up your garden. The blue shade is an uncommon color and will instantly draw your visitor's eye to wherever you plant it. The soft texture of the flowers provide a good contrast to harder edged blossoms and garden decor as well. It is an easy plant to grow and there are a number of choices available through commercial sources.