Illustration
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 2 years (a house reading).
Is Bluestar toxic to dogs or cats?
- Listed as toxic to dogs and cats by Royal Horticultural Society.
- Listed as poisonous to people by Royal Horticultural Society.
Lists differ and none is complete. If a pet eats a plant and seems unwell, call a veterinarian or a pet poison helpline.
What was checked
Nine facts were checked against named botanical sources, each recorded beside the sources that carried it: mature height and spread, hardiness zones, sun, water, bloom months and color, the trait tags, and years to mature size, which rests on a recorded house rule where no publisher states one and is marked so. Soil, diseases, pests, toxicity and the plant's own names have not yet been read for this plant, and its trait tags are the ones a feature uses rather than every word a page prints. Each fact above carries its own mark. 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, water, bloom months and color and trait tags were checked against 15 published sources on October 29, 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.
- Penn State Extensionheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- Plant Addictsheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- NC State ExtensionPlant Toolboxheight, spread, hardiness zones, sun, bloom months and color and trait tags
- 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
- University of Wisconsin HorticultureWisconsin Horticulture (University of Wisconsin-Madison Division of Ex...height, spread, hardiness zones, sun and trait tags
- Chicago Botanic Gardensun, water and bloom months and color
- Mt. Cuba CenterTrial Gardensun, water, years to mature size and trait tags
- RHSRoyal Horticultural Societysun and bloom months and color
- Lady Bird Johnson Wildflower CenterNative Plant Databaseheight and sun
- Missouri Botanical GardenPlant Finderbloom months and color
- Missouri Botanical GardenPlant Findertrait tags
How the checking works, and what each standard covers, is on the verified plants page.
Where it grows wild
Native to North America as a group
The 15 wild species sold under this name grow in 25 states.
United States: Alabama, Arizona, Arkansas, California, Colorado, Delaware, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Missouri, Nevada, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Utah, Virginia and 13 more
Range data from the World Checklist of Vascular Plants, Royal Botanic Gardens, Kew (CC BY 4.0, adapted) and USDA PLANTS. How the native range is credited.
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.
Common Black-Eyed Susan
Shares full sun and moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Decadence Deluxe Periwinkle Popsicle False Indigo
Shares full sun and moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Color Guard Yucca
Shares full sun and 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.
Feather Reed Grass
Shares full sun and moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Toyon
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.
Carnival Scotch Heather
Shares full sun and 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.
Buffalograss
Shares full sun and low to moderate water; blooms in early summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Sunflower
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.
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