University of Vermont Extension 
Department of Plant and Soil Science

News Article 

Perennial Plant Feature--Blue Stars

By Dr. Leonard Perry, Extension Professor
University of Vermont

 
Blue Stars. What a pretty name. And a very descriptive name, as the flowers resemble a mass of blue stars in early summer. They cover a perennial mound that is one to three feet tall and up to three feet across.

Named for Dr. Charles Amson, an 18th century scientific traveler in America, the plant is native to the south and central U.S. As such, it is good in native and naturalistic meadow plantings, massed in borders, or where you want a touch of blue. The long, narrow fruit pods (follicles) after bloom are also very attractive. It is one of the few perennials with very nice fall color, golden yellow in this case. A member of the Dogbane family, Blue Stars has a milky sap.

Being tolerant of many conditions, Blue Stars is low maintenance. It requires some cutting back in fall but that is about all that is needed, unless it is grown in part shade. Here, in the North, it can become leggy and may also need cutting back after flowering. It prefers full sun for best growth.

To propagate Blue Stars, cut stems in early summer for softwood cuttings. Rooting hormone will help. Plants may also be divided in spring or started from seeds. Soak seeds overnight in warm water, or hold in the moist cold (40 degrees F) for four to six weeks before sowing.

Too much fertility can make the plants leggy and cause them to fall over, so don't overfertilize Blue Stars. A well-drained, moist soil is best although soil preference will vary with individual species.

There are about 20 species, but only about six that are available at garden centers. Of these, the most common are Downy Amsonia (ciliata) and Willow Amsonia (tabernaemontana).

The first is native to the central U.S., hardy only in zones 6 through 9, and is found in dry, light woodland soils. It has dark green, lance-shaped leaves, which are hairy when young. Its flowers are sky blue.

The most common Blue Stars is probably the Willow Amsonia. The species (tabernaemontana) is named for German herbalist J.T. Tabernaemontanus. It is hardy in most areas, zones 3 through 9, and is found in moist woodlands. Its flowers are slate blue and the leaves wider than other species. Its fruit pods are held upright unlike some other species where the pods hang down.

A variety of this species, salicifolia, has leaves five to 10 times as long as wide, like willow leaves. The Willowleaf Blue Star has blue flowers with white centers.

For more details on Blue Stars, as well as on many other choice perennials, check out Perry's Perennial Pages (http://www.uvm.edu/~pass/perry/) on the Internet.


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