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PlantFiles: Southern Star
Oxypetalum caeruleum

Family: Asclepiadaceae (ass-kle-pee-ad-AY-see-ee) (Info)
Genus: Oxypetalum (oks-ee-PET-al-um) (Info)
Species: caeruleum (see-ROO-lee-um) (Info)

Synonym:Tweedia caerulea

30 members have or want this plant for trade.

Vines and Climbers

12-18 in. (30-45 cm)
18-24 in. (45-60 cm)
24-36 in. (60-90 cm)
36-48 in. (90-120 cm)

15-18 in. (38-45 cm)
18-24 in. (45-60 cm)

USDA Zone 8a: to -12.2 C (10 F)
USDA Zone 8b: to -9.4 C (15 F)
USDA Zone 9a: to -6.6 C (20 F)
USDA Zone 9b: to -3.8 C (25 F)
USDA Zone 10a: to -1.1 C (30 F)
USDA Zone 10b: to 1.7 C (35 F)

Sun Exposure:
Sun to Partial Shade

Unknown - Tell us

Bloom Color:
Light Blue

Bloom Time:
Late Spring/Early Summer
Mid Summer
Late Summer/Early Fall


Other details:
May be a noxious weed or invasive
Drought-tolerant; suitable for xeriscaping
Average Water Needs; Water regularly; do not overwater
Self-sows freely; deadhead if you do not want volunteer seedlings next season

Soil pH requirements:
6.1 to 6.5 (mildly acidic)
6.6 to 7.5 (neutral)
7.6 to 7.8 (mildly alkaline)

Patent Information:

Propagation Methods:
From softwood cuttings
From seed; direct sow outdoors in fall
From seed; sow indoors before last frost
From seed; direct sow after last frost

Seed Collecting:
Allow pods to dry on plant; break open to collect seeds
Properly cleaned, seed can be successfully stored

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7 positives
1 neutral
No negatives

Gardeners' Notes:

Positive Sandra13 On Apr 29, 2014, Sandra13 from Sacramento, CA wrote:

I have this plant in my garden here in Sacramento. This is the second year and it's doing well. We had a few consecutive nights in the 20's last Winter but it survived. I have no complaints about this plant except for the orange aphids that it attracts. It grows more like a small shrub for me. Love the color! I'm happy I planted it.

Positive RosinaBloom On Nov 24, 2013, RosinaBloom from Waihi
New Zealand (Zone 1) wrote:

Southern Star has perhaps more of an upright, trailing or twining habit.

Positive Domehomedee On Aug 8, 2013, Domehomedee from Arroyo Grande, CA (Zone 9a) wrote:

An Asclepia from South America. "Tweedia" is also called "blue milkweed". This was my first year growing this unusual diminutive plant, I say this because it remained under one foot tall. It did however bloom and seed, I have hopes it will survive the winter and get larger next year. I will be growing more of this as it has a true blue flower.

Positive zone10 On Apr 27, 2011, zone10 from San Diego, CA (Zone 10b) wrote:

This plant has one of the most true blue flowers I've seen. It is a tough plant and very showy in the springtime. In my frost free zone, this plant stays green year round and flowers repeatedly over several of the warm months. Flowers are followed by large seed pods that break open to reveal silky threads attached to flat, dark, round, seeds. They are carried by the breezes and germinate very easily. Seeds seem to remain in the ground until the following rainy season. Since they are all volunteers, I don't make an effort to water these plants and they have proven to be extremely tolerant of drought and heat. Oxypetalum coeruleum grows beside my cactus and succulents. A great plant for many reasons!

Positive LoriPo On Sep 6, 2008, LoriPo from Battle Creek, MI wrote:

This is one of my favorites because the flower is such a beautiful blue. It will grow as an annual in this area, but it is hard to find a source that sells it locally. This last spring I was fortunate to be at my favorite retail greenhouse when an employee brought out two flats of Tweedia. I was so excited! I may attempt to grow my own from the seeds I have just in case I can't find the plants next spring.

Positive pokerboy On Mar 19, 2005, pokerboy from Canberra
Australia (Zone 8b) wrote:

This plant gives beautiful blue flowers during summer and autumn in my climate. It is followed by bizzare, fluffy seedpods. They have a very soft texture. It is a strange blue you often do not find other plants giving. pokerboy.

Positive martina On Apr 29, 2004, martina from El Cajon, CA (Zone 10a) wrote:

Abundance of blooms of a very intersting lovely blue color and as a bonus somewhat bizarre seedpods afterwards. Fairly sturdy beautiful plant. My favorite.

Neutral Terry On Aug 30, 2001, Terry from Murfreesboro, TN (Zone 7a) wrote:

Dainty flowers start out as pink buds, opening to lavender or blue. Can be overwintered in a greenhouse, or grown as an annual in colder climates.


This plant has been said to grow in the following regions:

Arroyo Grande, California
El Cajon, California
Encinitas, California
Fremont, California
Long Beach, California
Los Angeles, California
Sacramento, California
San Diego, California
San Jose, California
Soledad, California
Vista, California
Deland, Florida
Navarre, Florida
Riverview, Florida
Snellville, Georgia
Battle Creek, Michigan
Elizabeth City, North Carolina
Trinity, North Carolina
Fair Play, South Carolina
Okatie, South Carolina
Austin, Texas
Garland, Texas

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