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Photo credits and licenses
Real photographs from naturalists and photographers worldwide, each used under its own license. Credit: Photo by Michelle W. （鍾偉瑋） / iNaturalist (CC BY), Photo by Michelle W. （鍾偉瑋） / iNaturalist (CC BY), Photo by Michelle W. （鍾偉瑋） / iNaturalist (CC BY) and Photo by Michelle W. （鍾偉瑋） / iNaturalist (CC BY). How photos are sourced →
Bluestar
Amsonia
Bluestar blooms from April through May.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Bluestar
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 4–9. Expect it to reach about 3 ft tall and 2.5 ft wide at maturity, in roughly 3 years (not yet checked).
What was checked
Mature height and spread, hardiness zones, sun and the trait tags were checked against named botanical sources for this plant. The bloom months and water need on this page were not, and each fact above says which. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Bluestar
Plant Bluestar in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 6, the middle of its hardy zones 4 to 9, spring means March to May and fall means August or September. Once settled, it blooms from April to May.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 6, the middle of this plant's hardy range, start with zone 6 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Bluestar get?
3 fttall5 ft 7 inan adult2.5 ftwideSee Bluestar in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Bluestar
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Bluestar about 2.5 ft apart, center to center, so each plant has room to reach its full width.
Add Bluestar to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Bluestar's height, spread, hardiness zones, sun and trait tags were checked against 11 published sources on July 30, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- NC State ExtensionPlant Toolboxheight, spread, hardiness zones, sun, years to mature size and trait tags
- bbg.orgBrooklyn Botanic Gardenheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones, sun and trait tags
- Missouri Botanical GardenPlant Finderheight, spread, hardiness zones, sun and trait tags
- NC State ExtensionPlant Toolboxheight, spread, hardiness zones, sun and trait tags
- NC State ExtensionPlant Toolboxheight, spread, hardiness zones, sun and trait tags
- Penn State Extensionheight, spread, hardiness zones, sun and trait tags
- University of Wisconsin HorticultureWisconsin Horticulture (University of Wisconsin-Madison Division of Ex...height, spread, hardiness zones, sun and trait tags
- Mt. Cuba CenterTrial Gardensun, years to mature size and trait tags
- Lady Bird Johnson Wildflower CenterNative Plant Databaseheight and sun
- Plant Addictshardiness zones and sun
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Bluestar
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note. A note reports what its source says; where that differs from a fact above, the fact above is this entry's stored value, and its mark says whether it has been checked.
Safety
When cut, stems and leaves ooze a milky white latex that is mildly toxic and can irritate sensitive skin. Wear gloves and keep the sap off skin and eyes. per NC State and Wisconsin
Worth knowing
Full sun does double duty: it produces the strongest gold fall color and the sturdiest, self-supporting habit. The shade that dulls color is what makes stems flop. per NC State and Penn State
When to cut back
Never cut before or during bloom. After flowering, either cut back by a third for a tidy mound, or leave the stems standing over winter for the bees. per NC State and Mt. Cuba
Zone range depends on species
Eastern bluestar is hardy in zones 3 to 9; threadleaf is cited narrower, 5 to 8 or 4 to 9. In zones 3 to 4, confirm your species first. per NC State and Penn State
Deer and rabbit resistant
Deer and rabbits leave it alone: the bitter, toxic milky sap makes the foliage unpalatable. A dependable pick where deer pressure is high. per NC State
Feeds early-season pollinators
Spring flowers draw native bees, hummingbirds, hummingbird moths, and butterflies. It is also a larval host, and hollow stems left standing shelter native bees. per Penn State
Essentially trouble-free
No serious insect or disease problems and no chemical inputs needed. Rust is an occasional, minor possibility. A tough, long-lived, low-maintenance perennial. per NC State
Deep taproot, drought tolerant
A deep taproot makes established plants drought tolerant, yet it also takes occasional wet feet and suits a rain garden. Slow to fill in. per Penn State
What pairs well with Bluestar
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
Sneezeweed
Shares full sun and moderate water; blooms in midsummer, extending the bed's season; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Perennial Sunflower
Shares full sun and moderate water; blooms in late summer, extending the bed's season; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Creeping Sedum
Shares full sun and low to moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter.
Lavender
Shares full sun and low to moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter.
Japanese Stewartia
Takes full sun to part sun and moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; taller at 16 ft, for the layer behind it.
Jasmine
Shares full sun and moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; climbs to 10 ft behind it, height without the footprint.
Feather Reed Grass
Shares full sun and moderate water; blooms in early summer as this one finishes; its seed heads stand through winter, for structure and the birds; taller at 5 ft, for the layer behind it.
Cleome
Shares full sun and moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; taller at 4 ft, for the layer behind it.
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Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.