Asclepias Physocarpa

Goose Plant for Monarch Caterpillars

Asclepias physocarpa: Gomphocarpus physocarpus, Goose plant, Giant swan milkweed, Hairy balls, Family jewels, Oscar, Cotton-bush, Balloon plant

Goose Plant Milkweed Seed Pods

Great Balls Of Milkweed!

Plant Specs:

  • Perennial for USDA hardiness zone 8 and above
  • Fast growing annual for colder zones
  • Full sun to part shade
  • Height: 4 to 6 feet (can grow taller)
  • Spacing: 2 to 3 ft
  • Flowers: white with purple accents
  • Blooms mid to late summer

Plant Propagation:

  • Start seeds indoors 2 months before final frost
  • Sow seeds directly after final frost (not recommended below zone USDA zone 8)
  • Soak seeds in warm water 24 hours before planting
  • Stem Cuttings in warm water
  • Leaf cuttings
  • In annual zones, balloon plants are better if you can find them locally or online

Asclepias physocarpa flowers in bloom

White Elegance with a Hint of Purple Passion


  • Fastest growing annual milkweed
  • Can sustain lots of monarch caterpillars late season
  • Long stems with pods make amazing table centerpiece
  • Use long cuttings to feed caterpillars indoors
  • Last viable milkweed species before fall takes over


  • Colder hardiness zones must start seeds indoors for hopes of a seed harvest
  • Flowers aren’t very showy, but still pretty
  • Up north, only pollinated by wasps (and one red admiral!)
  • Potentially difficult to overwinter? (I brought one in balloon plant that died. Perhaps it wasn’t getting enough light?)
WINTER 2014 UPDATE: I’m currently overwintering 3 balloon plants and they are all thriving under CFL light bulbs

Goose Growing Tips:

  • Start seeds indoors 1-2 months before avg last frost
  • Seeds germinate in less than one week with heat and moisture
  • Use a desk fan on seedlings to strengthen the stems to simulate an outdoor breeze…a must for strong stems!
  • Grow this as a back border so it doesn’t shade your other butterfly plants
  • Cut I- you can cut them back late spring for bushier growth
  • Staking may be required if not cut back in perennial zones
  • Cut II- Is fall setting in before seeds are ready to harvest? Take stem cuttings with the largest pods (leave seed pods attached) and place them in water. This should give them the time they need to finish developing.
  • Don’t force open seed pods…they will start to open when they are ready

Asclepias physocarpa milkweed pod starting to open up

Open Sesame!

Pollinator Plus:

Not much to report up north. The only pollinator I’ve noticed visiting this milkweed on a regular basis is the blue mud dauber (black wasp). If you have noticed other pollinators on the goose plant, please leave a comment below.

nature note: Though the mud daubers look ominous, they have never shown aggression. They’re also frequent visitors to our swamp and tropical milkweed plants.



One more time: starting seeds indoors early will give you a huge jump on the season. This milkweed species is a rare find in nurseries, so seeds are probably your only option.

Click here to Explore other Milkweed Options for your Butterfly Garden

Please post below if you have any questions or comments about growing Asclepias physocarpa in your garden:

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  1. By the way – they call G. physocarpus Bishop’s Balls in the UK and you can buy seeds and plants there. They sometimes get Danaus plexippus in the UK and a few people raise them.

    It grows so big here in NZ that I call it a “testicle tree”.

    • Hi Jacqui, thanks for the UK info and the scandalous new nickname. I tried to overwinter one so I could get a ‘tree-sized’ plant this season, but the plant died mid-winter. Maybe next year? I hope all is well in NZ!

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