Summary

This trial performed by Mt. Cuba Center’s horticultural research team evaluates the garden performance and ornamental qualities of Amsonia, a genus of beautiful, adaptable, and long-lived perennials. Commonly known as bluestars, Amsonia was named for 18th century Virginia physician and botanist John Amson. Most Amsonia are native to the United States and Mexico with two additional species found in Greece and Turkey (Amsonia orientalis) and Asia (Amsonia elliptica). In this trial, we included representatives of three native species, Amsonia ciliata, Amsonia hubrichtii, and Amsonia tabernaemontana, as well as numerous varieties, cultivars, and hybrids. The non-native A. orientalis was also included to allow for direct comparison to the native species.

Amsonia species and cultivars vary in their overall size and ornamental qualities such as foliage texture and bloom time, but all provide multiple seasons of ornamental interest. Spring brings sprays of blue flowers, followed by appealing summer foliage. Many bluestars wrap up the year with outstanding gold or orange fall color, particularly when grown in full sun. Bluestars support early-season pollinators including native bees and hummingbirds and are the host plant for several species of butterflies and moths. As with many members of the Apocynaceae family, including milkweed (Asclepias), Amsonia produce a milky sap that discourages browsing by deer and other mammals.

Amsonia grow well in a broad spectrum of soil types and sun exposure ranging from full sun to part shade. Bluestars are also exceptionally easy to care for in the landscape. A cutback and cleanup in late winter or early spring is all that is required in terms of yearly maintenance. Since Amsonia stems are hollow, leaving 12″–18″ of stem after the cutback has the added benefit of providing habitat for native bees. The key to growing Amsonia is patience. As with other long-lived perennials, bluestars take a few years to get established before they show their full potential for flowers, foliage, and fall color.

This trial evaluated 20 different Amsonia over a ten-year period and focused on their garden performance and ornamental qualities. Diseases were infrequently observed in this trial, and aside from minor chlorosis and rust, the plants were virtually pest and disease free. The Amsonia trial was grown in part-to-full sun in “average” soil, best described as clay-loam with a pH near 6.5. Throughout the trial, plants were given minimal care. Supplemental water was provided only during the first year after planting to encourage establishment. Mt. Cuba Center is located near Wilmington, Delaware and is within USDA hardiness zone 7a.

Click below to view and download the research report or scroll down for detailed descriptions about each plant in the trial (top performers plus all other plants tested) in alphabetical order.

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