Tharp's Blue Star Plant Care
Amsonia tharpii Woodson
Updated · Sources · How we source care data
Amsonia tharpii is a species of flowering plant in the family Apocynaceae, known by the common names Tharp's bluestar and feltleaf bluestar. It is native to New Mexico and Texas in the United States.
Every 7–10 days
Full sun to partial shade
50–85°F
40–70%
At a glance
How do you care for Tharp's Blue Star?
Water Tharp's Blue Star every 7–10 days, letting the top layer of soil dry out between waterings, and give it full sun to partial shade. It prefers temperatures of 50–85°F (10–29°C) and 40–70% humidity. Fertilize it every 6 months during the growing season.
Where Is the Tharp's Blue Star Native To?
What Is the Tharp's Blue Star?
Tharp's Blue Star (Amsonia tharpii) belongs to the Apocynaceae family within the Amsonia genus. Tharp's Blue Star is native to New Mexico and Texas in the United States. Tharp's Blue Star is also known as Blue Star.
Tharp's Blue Star displays a clump-forming perennial growth habit, reaching up to 2.5 ft tall with a spread of approximately 2 ft. Tharp's Blue Star produces clusters of small, star-shaped blue flowers.
Leaf size: approximately 4 inches.
How Often Should You Water a Tharp's Blue Star?
Amsonia tharpii requires watering every 7–10 days. Allow the top layer of soil to dry between waterings to prevent root rot. Reduce watering frequency during winter when growth slows.
Watering Frequency
Every 7–10 days
Let soil partially dry between waterings
What Light Does the Tharp's Blue Star Need?
Tharp's Blue Star thrives in full sun to partial shade.
Light Requirement
Full sun to partial shade
What Temperature and Humidity Does the Tharp's Blue Star Prefer?
Amsonia tharpii grows best at temperatures of 50–85°F. Tharp's Blue Star prefers humidity levels of 40–70%.
Temperature
50–85°F
Humidity
40–70%
What Soil Mix Works Best for a Tharp's Blue Star?
Well-draining, fertile soil with a mix of sand and organic matter. Good drainage is essential for Tharp's Blue Star to prevent waterlogging, which leads to root rot and fungal issues.
How Often Should You Fertilize a Tharp's Blue Star?
Feed Tharp's Blue Star every 6 months during the growing season (spring and summer) with a balanced fertilizer diluted to the strength on the label.
Pause feeding in autumn and winter, when growth slows, and never fertilize dry soil — water first.
Fertilizing
Every 6 months
During the growing season
The PlantoScan app can remind you when to water and when to fertilize each plant.
How Do You Repot a Tharp's Blue Star?
Repot every 2-3 years in early spring. Choose a pot one size larger than the current container, and ensure it has drainage holes to allow excess water to escape.
How Do You Propagate a Tharp's Blue Star?
Tharp's Blue Star can be propagated through division, stem cuttings, seeds. Similar propagation techniques also apply to fringeleaf blue star plant care, which shares the same genus.
Is the Tharp's Blue Star Toxic to Pets and Children?
Pet safety not verified
The ASPCA does not list Tharp's Blue Star, so we can't confirm whether it is safe for cats and dogs. Keep pets from chewing it as a precaution.
This is a general caution, not veterinary or medical advice. If your pet ate a plant, contact your vet or animal poison control.
See all plants toxic to cats and plants toxic to dogs.
What Pests and Diseases Affect the Tharp's Blue Star?
Tharp's Blue Star is susceptible to aphids, spider mites, whiteflies. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.
Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.
What USDA Hardiness Zone Does the Tharp's Blue Star Need?
Tharp's Blue Star grows outdoors in USDA Zone 12a. It survives winters down to planting zone 12a. Tharp's Blue Star is native to New Mexico and Texas in the United States. In cooler regions, grow Tharp's Blue Star as a houseplant or bring it indoors before the first frost.
Hardiness Zone
Zone 12a
Keep exploring plants
Tharp's Blue Star is one of many species covered in the complete plant care and identification guide, which groups plants by genus, attribute, and popularity.
It belongs to the Amsonia genus — compare its care with other Amsonia species on PlantoScan.
Amsonia is part of the Apocynaceae plant family — browse all Apocynaceae genera and species.
Tharp's Blue Star thrives in bright light and direct sun — see other bright-light plants.
Related Plant Care Guides
Closely related plants with similar care requirements:
Sources
- Scientific name & taxonomy: Amsonia tharpii Woodson, family Apocynaceae (first published in Ann. Missouri Bot. Gard. 35: 237 (1948)) — World Flora Online record, IPNI name record.
- Pet toxicity: Pet safety not verified: the ASPCA does not list Tharp's Blue Star, so we can't confirm whether it is safe for cats and dogs. Checked against the ASPCA plant list; any other toxicity note on this page comes from PlantoScan's plant database.
- Hardiness zone: USDA Zone 12a, calculated from the plant's minimum temperature.
- Care values(watering, light, temperature, humidity, soil, fertilizing): PlantoScan's plant database, filtered by automatic plausibility checks — values that fail them are hidden. How we source and check plant data.
Spotted a mistake? Email info@upvision.media with the page link — we check and correct reported errors.
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