BLUE AGERATUM CONFUSION
When is an ageratum not an ageratum? When it’s a eupatorium. If these words mean absolutely nothing to you, you’re not alone. Even though ageratum are stalwarts of public plantings from gas stations to parks, the name doesn’t trip off the tongue like “zinnia” or “sunflower.” But if you want sturdy garden plants with true blue or blue-purple flowers, you should try both annual ageratum and Eupatorium coelestinum. The latter can confuse people, as it is often called “hardy ageratum.”
Annual garden ageratum is also known by the more poetic name, “floss flower,” with the “floss” descriptor referring to the fluffy flowerheads. Most of the popular varieties are a stunning shade of medium blue, though you can also find purple, pink and even white ageratum. In the spring, low-growing, hybrid ageratum shows up at every garden center, big box store and nursery in America. Shortly thereafter, millions of these plants go into beds, borders and pots all over the country. Placed in sunny spots, they bloom reliably until frost, amply justifying the genus name, which comes from the Greek word “ageras”, meaning non-aging. Ageratum cover themselves with so many blossoms that it’s sometimes hard to see the oval-shaped leaves.
The best thing about annual ageratum is that it plays well with others. It looks wonderful combined with anything yellow, hence the frequent marigold/ageratum combination. You can also combine it with yellow cosmos or sunny-hued petunias. Older varieties needed deadheading, but most of the currently-popular types simply cover the spent flowerheads with new ones.
Every fall, as frost closes in, ageratum shares the fate of impatiens, coleus and all the other popular garden annuals. It dies. This is because its native habitat is Florida, Mexico, South America and parts of the West Indies. Cold weather pushes it towards the compost bin rather than the dormancy that overtakes perennials.
If you don’t want to replant ageratum each year, there is an alternative–Eupatorium coelestinum, sometimes called hardy ageratum, mist flower or blue boneset. At this time of year you see its pesky relative, Eupatorium perfoliatum all over the place. It’s the tall plant with the fluffy white flowers that pops up at random in home gardens, untenanted spaces and just about anywhere else it pleases. I weed it out of my beds every year and the following year it returns undaunted. Eupatorium is tough.
Eupatorium coelestinum seems better-mannered than some of its eupatorium relatives. It has the same blue flowers as annual ageratum, but, when installed in a congenial situation, it returns reliably every year. At about fifteen inches tall, it is a little more statuesque than the most popular of the annual varieties. It also begins blooming later in the spring. This is not a bad thing. If your garden doesn’t already contain enough plants to make a splash in the early spring; something is very wrong. The beautiful blue of Eupatorium coelestinum makes a much more important statement later in the season. I saw one not long ago, still going strong in late September, growing alongside some tall white cosmos. The effect was lovely in the soft light of an autumn afternoon.
Like Joe Pye-weed, another popular eupatorium, hardy ageratum is perfect for native plant garden. It would be equally at home in an herb garden. Blue bonset and its white-flowered relatives were used by Native Americans and early settlers as an antipyretic or fever reducing agent. When leaves and/or flowers were brewed into teas, the liquid helped combat dengue fever, which is also sometimes called “bone-break fever” due to the severe joint pain that is one of the symptoms.
Eupatorium coelestinum is a sun lover that also flourishes best in damp soil. Mulching will help keep the roots cool and moist, but you may have to add supplemental water during dry periods. The blue or bluish purple flowers are good mixers, combining especially well with yellows, oranges, pinks and whites. Next year I may combine vivid orange Mexican sunflower or tithonia with blue ageratum to attract both butterflies and compliments from the neighbors.
Annual ageratum is easy to get from just about any garden center. However, if you want to try growing it from seed next spring, you can obtain those seeds from W. Atlee Burpee & Co., 300 Park Avenue. Warminster, PA 18974; (800) 333-5808; www.burpee.com. The catalog is free. Eupatorium coelestinum is available from Niche Gardens, 1111 Dawson Road, Chapel Hill, NC 27516, (919)-967-0078; www.nichegardens.com. Free catalog.