Amsonia (bluestar)

About Amsonia (bluestar)

Bluestars are tidy, long-lived native perennials with clusters of small, pale-blue, star-shaped flowers in spring and willowy leaves that turn bright gold in fall, so they look good for three seasons (Iowa State, Mt. Cuba Center). Eastern bluestar is native from Maryland and southeast Virginia to southern Illinois and Kansas, south to Florida and east Texas, while threadleaf bluestar comes only from the Ouachita Mountains of Arkansas and Oklahoma (Wildflower Center, NC State) and was Perennial Plant of the Year in 2011. A milky sap makes deer leave them alone but can irritate skin.

Eastern bluestar is hardy in zones 3-9 and threadleaf bluestar in 5-8 (NC State, Wisconsin Extension); most other bluestars are hardy to zone 5 (Iowa State). Not listed as invasive; eastern bluestar has naturalized north to Massachusetts (Wildflower Center).

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Plant in spring or fall where it can stay: the dense crown and taproot make older plants hard to move or divide (Iowa State, Wisconsin Extension). Divide in early spring or fall if needed, with at least one bud per piece (NC State). Fresh seed sown outdoors right after collection sprouts quickly; stored seed needs 4-6 weeks of cold, moist treatment, and seedlings bloom in their second or third year (Wildflower Center, Wisconsin Extension). Plants take a few years to fill out (Mt. Cuba Center). No sourced day count to first bloom.

Soil

Average, well-drained loam is ideal, but it adapts to clay and, once settled, dry soil. Eastern bluestar likes more moisture; threadleaf and fringed bluestars prefer drier ground. Rich soil or shade makes plants flop (NC State, Iowa State, Wisconsin Extension).

Average, well-drained soil is enough; don't enrich it heavily, because rich soil makes bluestars open and floppy (NC State, Wisconsin Extension).

Feeding

Over-fertilizing gives open, floppy plants (Wisconsin Extension), so feed only if a soil test calls for it (Penn State). Too much shade also causes flopping. Wear gloves when cutting: the milky sap can irritate skin.

Harvest

Blooms for 2-4 weeks from mid-April into May or early June (Iowa State, Wisconsin Extension); gold fall color follows, best in full sun. Flowers last well when cut (Wisconsin Extension). After bloom, cut stems back by a third to a half for a rounder, sturdier plant and to stop seedlings (Wisconsin Extension, Iowa State). Wear gloves: the sap can irritate skin.

Varieties (14)

Wisconsin Extension, Iowa State, NC State and Mt. Cuba Center's 2013-2023 bluestar trial document these 14 bluestars; some are close relatives (fringed bluestar and hybrids) rather than selections of the two main species.

Good neighbors

Iris, Milkweed, Daylily, Sedum (stonecrop), Garden ferns (ostrich, Christmas, lady, Japanese painted), Sedges (Carex), Bleeding heart

Wisconsin Extension suggests Siberian iris, butterfly weed, daylilies, fall sedums, ferns, sedges and bleeding heart as good-looking garden partners; this is a design pairing, not a pest-control claim.

Diseases and problems

Rust

In the kitchen

Safety: Leaves and stems bleed a white latex sap that is considered toxic and can irritate sensitive skin, so wear gloves when cutting it back (Wisconsin Extension, NC State, Iowa State). Not a food plant; keep children from chewing it.

Pets: Not listed by the ASPCA (no amsonia or bluestar entry on its dog, cat or horse lists). Its milky sap is considered potentially toxic (Iowa State), so keep pets from chewing it.