How to Grow Oxypetalum Plants

Guide to Growing Southern Star, Tweedia and Blue Flowered Milkweed

Oxypetalum plants are a genus of climbing plants that may reach about 90 cm (3 feet) in height.

Although they are half hardy perennials, Oxypetalum are often grown as half hardy annuals in the garden.

Oxypetalum caeruleum
Oxypetalum caeruleum by H G M; Creative Commons.

They carry deep green foliage and bloom in the summer through to autumn with pale blue stellar flowers.

Some common names for Oxypetalum include Southern Star and Star of the Argentine.

Blue Flowered Milkweed
Oxypetalum coerulea - Blue Flowered Milkweed by Hankyhelper. Photographs under creative commons licence.

How to Grow Oxypetalum Plants

The seeds of Southern star and other Oxypetalum plants should be sown at a depth of 6 mm (1/4 inch) following the last frost of spring.

Southern Star likes to grow in a sunny part of the garden that has good drainage. Ideally the soil should be rich and loamy, but this is not essential.

You can start to grow Southern Star indoors first. Do this about six weeks in advance. The seeds will take about two weeks to germinate at 21 degrees Centigrade (70°F).

Once growing, transplant the young Southern Star seedlings outdoors in mid spring, after the last chance of a frost. They should be spaced from about 15 to 20 cm (6 to 8 inches) apart.

Caring for Southern star and other Oxypetalum Plants in the Garden

It is easy to look after Southern Star and other Oxypetalum species. The young plants should be pinched back to encourage branching.

They are a climbing plant, so supply Oxypetalum with a support to grow upon.

If you require more Oxypetalum plants, then they can be propagated by taking cuttings in the spring time.

Oxypetalum Plant Growing and Care Guide

Common Names: Southern Star, Blue Flowered Milkweed, Star of the Argentine, Tweedia.
Life Cycle: Half hardy perennial commonly grown as a half hardy annual by gardeners.
Height: 40 inches (100 cm).
Native: South America.
Growing Region: Zones 2 to 10. As a perennial in zones 9 and 10.
Flowers: Summer and autumn.
Flower Details: White, blue. Speckled. Star-shaped.
Foliage: Grey-green, green. Downy. Cordate.
Sow Outside: 1/4 inch (6 mm). Following the last frost or in autumn. Spacing 8 inches (20 cm).
Sow Inside: Germination time: one to two weeks. Temperature 70°F (21°C). Seven or eight weeks in advance. Transplant outdoors a few weeks after the last frost; temperatures should not drop below 41°F (5°C).
Requirements: Full sunlight. Rich soil. Sandy soil. Can survive in dry soils. Pinch tips. Propagate: cuttings in the spring.
Family: Apocynaceae.
Miscellaneous: Tweedia is synonymous with Oxypetalum.

Common Questions

How many members does the Oxypetalum genus contain?

The Oxypetalum genus is small, with about 15 species. These plants are native to South America.

Do Oxypetalum members make a good garden or landscaping plant?

Members of the Oxypetalum genus are not commonly seen in gardens, but they can make intriguing additions to a diverse collection due to their unique floral structures.

Which Oxypetalum species are most frequently grown by gardeners?

The most frequently grown species is likely the Southern Star (Oxypetalum coeruleum), appreciated for its star-shaped blue flowers.

Are Oxypetalum plants fragrant?

There is no widespread documentation of Oxypetalum plants being notably fragrant.

What is the perfect location to grow Oxypetalum?

Generally, Oxypetalum prefers a sunny location with well-drained soil. As a less common genus, specific cultivation practices may vary depending on the species.

Is Oxypetalum invasive in the USA, if so in which states?

Presently, Oxypetalum is not listed as an invasive genus in the USA.

How do I remove Oxypetalum plants from my garden?

If you need to remove Oxypetalum, dig up the plant, ensuring the entire root system is removed to prevent regrowth.


The Oxypetalum plant genus is part of the Apocynaceae family and comprises perennial and annual plants. They are commonly known as milkweeds. Known for their star-shaped flowers, they offer an attractive floral display.

Generally, Oxypetalum prefers full sun and well-drained soil. Planting can be carried out in spring. These plants can add interest to borders, rockeries, or container gardens, especially due to their unique flower form and often intense flower color.

I hope that you enjoyed this guide on how to grow Oxypetalum plants. You may also enjoy the following Gardener's HQ growing guides: How to grow Allamanda cathartica, Ficus benjamina, and Vinca minor plants.