Native Amsonia for the Home Garden

These herbaceous perennials provide reliable ornamental interest for months. Amsonia's foliage is attractively textural and matures to a late-season color change. Common leaf shapes are either "willow or lance" or "thread."  Thread-like leaf species display a soft, fine texture with a billowy or airy look, while willow and lance forms appear coarse in texture. In fall, the foliage offers varying yellow to gold color changes. Thread-like species have the showiest golden foliage of all. Commonly called bluestar, this versatile plant works well in a garden in front of a border, as a specimen planting, in drifts, or mixed with naturalistic wildflowers and ornamental grasses.

In November, a stunning show of golden-yellow foliage from a mass planting of threadleaf bluestar. Thomas J. Mrazik, Penn State Master Gardener

Amsonia spp. are clump-forming plants that develop from a semi-woody growing crown called a caudex. These produce upright, multiple leafy stems that grow into a shrub-like v-shaped form. Foliage is abundant, dense, medium green in color, and long-lasting. Bluestar is easy to care for and resists most diseases and pests.

Native bluestar supports pollinators, including native bees and hummingbirds. It is a host plant for caterpillars of several butterflies and moths. Routine maintenance in winter or early spring involves cutting back the stems, which are hollow. Be sure to leave 12 to 18 inches of stem as part of the cutback, providing habitat for native bees.

Most native species in the Amsonia genus do well in hardiness zones 4 to 9. They prefer a range of full sun to partial shade, but too much shade can cause them to become open and floppy. Moist soil conditions are best. Mature plants, however, can tolerate dry spells because of a deep taproot and dense fibrous roots. They reach heights of 3-4 feet and a similar, if not greater, width. Cultivars of shorter height are available.

Though it is long-lived, bluestar requires time to develop its fullest features. Routine division is not usually needed unless a plant outgrows its space or impedes nearby plantings. Be aware that the taproot system of a mature plant makes it difficult to extract from the ground. Dig deep and wide if the intention is to transplant or divide. A division must include the long taproot with attached eye buds, the dense fibrous roots, and the surrounding soil. On the other hand, small seedlings are easy to transplant. 

Amsonia's extensive below-ground root structure is comprised of eye buds, thick taproots,  and dense fibrous side roots. Thomas J. Mrazik, Penn State Master Gardener

Grow amsonia from seed by direct sowing. Pollinated flowers make clusters of elongated cylindrical follicles, which release seeds when they split open. They readily germinate, but plants don't flower until the second or third year.

Bluestar flowers are small but abundant. The blue is deepest as buds emerge and lightens as the flower ages. A flower is ½ to ¾ inch across, consisting of five spreading petals fused into a tubular corolla with a calyx at its base. The corolla houses its reproductive parts, pollen, and nectar. There is no noticeable floral fragrance.

A sea of breathtaking flowering clusters from a mass planting of lance-leaf Amsonia. Thomas J. Mrazik, Penn State Master Gardener

After flowering, careful pruning promotes bushier foliage and shorter, sturdier stems, if desired. Wear gloves when pruning because stems and leaves have a white latex-like sap, which irritates sensitive skin.

The plant blooms from mid-April to early June, with flowers lasting about 2-4 weeks. Its inflorescence is branching with dense clusters on terminal compound cymes. While an individual plant's flower display varies across some species, mass or drifts of multiple plants can be breathtaking, not just in flower but throughout much of the year.