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Ageratum is a pretty plant in a pleasing palette

If you are looking for a short, blue plant to edge a flower bed (and probably, you're not), try ageratum.

Blue blooms in the garden are difficult to come by, especially on well-behaved plants that spread out a little, mound up nicely and bloom all summer. Ageratum does all that.

Ageratum, A. houstonianum, grows to about 6 inches tall. The blooms appear in clusters and are fluffy, completely covering the little heart-shaped leaves by summer's end. The flower clusters will eventually grow to more than 4 inches across and are self-cleaning.

This plant blooms better when planted in sun. Morning sun and afternoon shade are really best because hot afternoon sun scorches the flowers. It likes a little moisture, so plant it on the downhill side of your raised beds. It thrives in containers if not allowed to dry out for long periods.

Ageratum's only serious pest is whiteflies. They lurk on the undersides of the leaves. You'll notice leaf curl and little flies darting about when you shake the plant. Because spraying insecticidal soap under the leaves is not so easy, I pull infested plants out and put them in plastic bags in the trash can. There, take that!

Flossflower, as ageratum is sometimes called, comes in colors that hang around on the color wheel near blue - purple, pink, burgundy and white. The Victorians loved ageratum and planted it in masses to create garden designs. This is the same technique we see on ditch banks in the spring that have been planted with blue, white and pink phlox, P. subulata. (We call that plant "Thrift" for some reason.)

Ageratum is easier to grow than to photograph. Photographers complain that the blooms of the blue ageratum appear in all pictures to be pinkish-purple. They even have a name for the problem: the ageratum effect.

There is a tall selection called "Blue Horizon" that grows about 2 feet tall and would make a nice back-of-the-border plant. The blooms appear on long, sturdy stems, and they are reputed to dry well and have a very long vase life. My search through the wheelbarrow-load of catalogs I have has not produced a source.

Flossflower can be grown from seed, but the easiest thing to do is buy plants from the nursery in spring.

I've never seen a tray of them that wasn't root-bound - they have masses of fibrous roots - so cut an X across the roots and spread them out before you plant them.

Maybe I will plant some pink ones in a container next year, backed with sweet alyssum and purple petunias.

Winder resident Dora Fleming is a Georgia master gardener. E-mail her at dfleming1@earthlink.net.