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PlantFiles: Swan Plant, Balloon Plant, Cotton-bush, Oscar, Hairy Balls, Giant Swan Milkweed
Gomphocarpus physocarpus

Family: Apocynaceae (a-pos-ih-NAY-see-ee) (Info)
Genus: Gomphocarpus (gom-fo-KAR-pus) (Info)
Species: physocarpus (fy-so-KAR-pus) (Info)

Synonym:Asclepias brasiliensis
Synonym:Asclepias physocarpa
Synonym:Gomphocarpus brasiliensis

4 vendors have this plant for sale.

36 members have or want this plant for trade.

Tropicals and Tender Perennials

36-48 in. (90-120 cm)
4-6 ft. (1.2-1.8 m)
6-8 ft. (1.8-2.4 m)

36-48 in. (90-120 cm)
4-6 ft. (1.2-1.8 m)

USDA Zone 6b: to -20.5 C (-5 F)
USDA Zone 7a: to -17.7 C (0 F)
USDA Zone 7b: to -14.9 C (5 F)
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)

Sun Exposure:
Full Sun
Sun to Partial Shade

All parts of plant are poisonous if ingested

Bloom Color:
White/Near White

Bloom Time:
Mid Summer
Late Summer/Early Fall


Other details:
Drought-tolerant; suitable for xeriscaping

Soil pH requirements:
5.6 to 6.0 (acidic)

Patent Information:

Propagation Methods:
By dividing the rootball
From leaf cuttings
From seed; direct sow outdoors in fall

Seed Collecting:
Bag seedheads to capture ripening seed
Allow pods to dry on plant; break open to collect seeds
Allow seedheads to dry on plants; remove and collect seeds
Properly cleaned, seed can be successfully stored

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10 positives
6 neutrals
1 negative

Gardeners' Notes:

Positive onebirdiema On Aug 28, 2014, onebirdiema from NoVa, VA (Zone 7a) wrote:

This plant 'volunteered' in my vegetable garden summer before last. It was The Mystery Plant until someone from local Coop Ext id'd it for me. By end of summer we counted five monarch caterpillars crawling all over it. After frost I moved it out of the vegetable garden, but we then had a hundred-year cold winter and it didn't come back. I do, however, have seed in the gomphos I saved, and will be trying various things to germinate some. Then I propose to entertain the drivers on my suburban subdivision street by planting them along the curb . . . if they'll grow there, they'll grow anywhere! THanks for all the comments previously -- they are a big help.

Neutral Domehomedee On Sep 27, 2013, Domehomedee from Arroyo Grande, CA (Zone 9a) wrote:

I'm not impressed with the flowers or the attracting ability of this milkweed. The seed pods are interesting but have taken quite a while to mature in my garden. I had someone comment that they look like oleander bushes, and they do when they aren't podding. I like other Asclepias much more, for attracting butterflies and for the fact that tall bushes with aphids are harder to dispose of at the end of the season than small bushes with aphids.

Positive AmandaEsq On Mar 17, 2013, AmandaEsq from Greensboro, NC (Zone 7b) wrote:

I purchased this seed from a reliable vendor who caters to monarch enthusiasts. My understanding is that it is an annual in my zone. The seed did not require pretreatment of any sort. I can't imagine why anyone here has identified difficulty in germinating the seed. If you have wild collected the seed it may be that the seeds weren't ready for harvest.

The plants grew to at least 6' tall and were alive well past frost here. I wondered myself if they really were going to be annual in my zone. We did have extended periods of sub-freezing temperatures this winter (unlike last) so I'll be watching the stalks with great interest. I collected a great amount of seed and will start more for this season.

If you grow this plant you should expect aphids. Milkweeds are synonymous with both aphids and Monarchs. I grow several kinds of MW, and while most caterpillars are found on the tropical milkweed (A. curassavica) the cats will also eat the foliage of this plant as a substitute if you are running low.

Asclepias physocarpa (aka: Gomphocarpus physocarpus)
Monarch butterfly host plant
White flowers
Native to South Africa
Frost sensitive perennial
60" - 72" tall
Blooms from May until first frost
Cold hardy in USDA zones 10 - 11
Summer annual in USDA zones 3 - 9

Growing Instructions: Start seeds outdoors in the spring after the danger of nighttime freezing has past. Pick a location with full sun and prepare soil for good drainage, if needed. Plant seeds 1/8" deep and 36 apart, using 3 seeds per hole. Keep the soil evenly moist until the seeds germinate in 10 - 20 days. Once the seedlings reach 1", thin out so you have individual plants spaced 36 apart. Water regularly allowing the soil to go nearly dry between each watering. Fertilize monthly in the summer with a general purpose fertilizer. To get a head start, seeds can be planted indoors in the late winter. Transplant outdoors after the danger of nighttime freezing has past.

Neutral Leafhead On Mar 7, 2013, Leafhead from Madison, WI wrote:

I'm just starting out c Asclepias physocarpus seeds for my first time. I'm a long time butterfly gardener and this Asclepiad intrigues me as a host plant/ nectar source.
I live in Zone 4b (WI) and am hoping this will reseed itself here in the Midwest.
If all else fails, I'll keep some seed back for next year...

Positive fwingsuk On Oct 5, 2012, fwingsuk from Warwick
United Kingdom wrote:

got these seeds in SA planted them in doors and everyone germinated six plants the rest are in the fridge the plants are in pots in the garden and have flowers on now but I think there will not be any seed heads as it is already 10c.
Can anyone tell me if I put these in a green house that they will survive till next year they are already 4 foot high with loads of buds on
many thanks

Neutral wyopaul On Aug 23, 2012, wyopaul from San Diego, CA wrote:

the most important function this plant provides; in addition
to it's fun name and appearance; is that it is a Monarch
Butterfly attractant. The lady who complained about
caterpillars all year probably had a lot of monarchs
munching and making a mess, but what a bonus!
People who grow this plant in monarch areas are providing
much needed egg laying spots, and food for future generations.
I live in San Diego, and am seeing far more monarch in the yard, and yes, the caterpillars are munching.

Positive silkroad On Mar 28, 2011, silkroad from Lady's Island, SC (Zone 9a) wrote:

I love this plant! I have found it easy to germinate, and the dried balloons look great with other dried flowers, or just piled into bowl on the coffee table. They always generate comment. The flowers, too, while not showy, are graceful and often the plant grows into a lovely candelabra shape. My friends always look forward to the seedlings I germinate for them.

Neutral murchik On Aug 12, 2010, murchik from Pedricktown, NJ wrote:

I have limited experience with this plant so far-started it from seeds this spring. Seeds were from 2 different sources. One pack from Chiltern Seeds, UK; using baggie method, half w and half w/o cold stratification none germinated. Another pack from Hardyplants; using baggie method, soaked seeds in 100 F and let sit overnight-7 out of 10 seeds germinated. One germinated during original overnight soak, the other 6 in a baggie within a week.
jxbrad14 I saw this plant in Longwood Gardens this year, too. Unfortunately, there was nobody around at the time to ask if it survives the winters or they grow it as an annual.
Maybe, the seeds you picked were immature or they might require a period of dormancy to become viable.
I have my seedlings planted out in two places in the garden. One is more sheltered than the other. I also have 2 plants potted up to take inside for winter.We'll see how they make it.
We are infested with Monarch butterflies this summer. I am constantly moving Monarch caterpillars from Oscars milkweed to the wild ones that grow around, but find new ones on mine all the time. My plants are still rather small and having all the leaves eaten off of them is not going to help them get bigger and stronger. I am glad Monarchs are making a comeback, though.

Negative jxbrad14 On Jun 10, 2010, jxbrad14 from Lansdowne, PA wrote:

Found seeds on a plant growing at Longwood Gardens, Kennett Sq. PA. and tried sowing them outdoors and indoors into peat moss pod. Out of 20 seeds none germinated.

Positive jlp222 On Feb 21, 2010, jlp222 from Hammond, LA (Zone 8b) wrote:

This is the first Milkweed I grew. I planted about 10 seeds directly in my garden and 2-3 grew (my fault not the seeds, I was a beginning gardner). This was 3 years ago. Last year, only 2 came back. One grew very bushy to about 4 feet. The other to a lanky 6 feet. They are a caterpillar beacon! They were covered all summer and into fall. Also, I had a problem with aphids. There had to be thousands of them.

The seed pods ("balls", hehe) are so very interesting that I would grow this plant for those alone. They are amazing cut and dried, and everyone who walks past had to ask about them.

So pretty much you have:

Strong grower
Give butterflies and caterpillars a home
Very cool seed spods

Also attract aphids (yuck!)

I will always have one of these in my garden. Jennifer

Positive Arline On Jan 25, 2010, Arline from Palo Alto, CA (Zone 9a) wrote:

I live in Palo Alto, CA and have grown this Asclepias for 2 years. The branches make a wonderful dried arrangement and it is a real attention getter at over 6 feet when the swollen seed pods sway in the breeze. No cats yet though.

Positive SusiS On Nov 8, 2009, SusiS from San Leandro, CA wrote:

I planted it from seed last fall, and now it is about 8 ft and growing. I am not sure if I should cut it back in the winter. It is growing above the roof!

Positive VGMKY On Nov 12, 2008, VGMKY from Louisville, KY wrote:

This was my first year growing Oscars Milkweed or asclepias (Gomphocarpus physocarpus) here in Louisville, Kentucky. It did outstanding growing to better than six feet tall. I volunteer at a local nursery and was able to germinate the seed there in late March. and transplanted them in early May. There is a 120/130 days needed for maturity. being late Summer/Early Fall with flowering and pods. With high heat and dry weather it was drought-tolerant.
Seed saving can be a challenge; I didnt want them to dry attached to the fluff so took the mature pods and separated the seed from the center of the pod and using my fingers rubbed the seed and they detached themselves into a container for drying. I found this method helpful to me rather than having the milkweed fluff escaping in the house of flying around my head.

Neutral kittysue On Nov 9, 2008, kittysue from Fairborn, OH wrote:

Seed are slow to germinate. The plant is a fast grower in ordinary potting soil, and relatively free of oleander aphids.

Positive flamingonut On Sep 6, 2007, flamingonut from New Milford, NJ wrote:

A beautiful tall milkweed. Earlier on, it had quite a few tiny monarch cats on it, and I believe the high amount of wasps & predators did them in. I've seen conflicting hardiness info on this, ranging from Z7 thru Z10 and Z9 thru Z10. Regardless, it's a must have annual for us northerners. Hopefully I'll be able to harvest seed so I can grow more next year. It just started blooming in NJ, late August, originally wintersown.

Neutral ineedacupoftea On Dec 25, 2006, ineedacupoftea from Denver, CO wrote:

Similar to Asclepias fruticosa, but a larger plant in general; also from South Africa.

Positive hedgwytch On Oct 8, 2006, hedgwytch from Tulsa, OK wrote:

This is a monarch magnet! I grew four other Asclepias in my garden this year, and this was the one that was consistently covered in cats all season long. The seed pods are a definite conversation starter! This plant gets a thick stalk and about 7 feet tall in Z7. The flowers are small, cream and pale lavender, and hang in clusters. I plan on adding several more to next year's garden. This is a must-have in a butterfly garden.


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

Tempe, Arizona
North Little Rock, Arkansas
Arroyo Grande, California
Calistoga, California
El Sobrante, California
Encinitas, California
Palo Alto, California
Rancho Palos Verdes, California
Richmond, California
San Diego, California
San Jose, California
San Leandro, California (2 reports)
San Marcos, California
Vista, California
Denver, Colorado
Brooksville, Florida
Deland, Florida
Homestead, Florida
Indialantic, Florida
Port Saint Lucie, Florida
Saint Petersburg, Florida
Buford, Georgia
Cordele, Georgia
Hilo, Hawaii
Barbourville, Kentucky
Louisville, Kentucky
Hammond, Louisiana
Dighton, Massachusetts
Dearborn Heights, Michigan
Minneapolis, Minnesota
New Milford, New Jersey
Elizabeth City, North Carolina
Greensboro, North Carolina
Middletown, Ohio
Oklahoma City, Oklahoma
Tulsa, Oklahoma
Portland, Oregon
Ladys Island, South Carolina
Ninety Six, South Carolina
North Augusta, South Carolina
Austin, Texas (2 reports)
Dallas, Texas
Los Fresnos, Texas
Richardson, Texas
Hampton, Virginia
Bellevue, Washington

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