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Gomphocarpus physocarpus

Gomphocarpus physocarpus
pufferfish milkweed; balloon cottonbush
Gomphocarpus physocarpus

Synonym(s) Asclepias physocarpa
Common name pufferfish milkweed; balloon cottonbush
Family apocynaceae
Life cycle tender perennial (Z7-10)
Flowers white/pink (late summer)
Size 3-6'
Light sun-part shade
From seed germinate at room temperature
detailed seed-starting info below

The common names refer to the seedpods, shaped like hairy balloons. The individual flowers look much like those of their close relatives, the Asclepias species, but are borne in looser clusters. In my first attempt to grow them, I planted them out in late spring, in a partly shaded area. The plants took a long time to reach any size, and didn't bloom till the second half of October - too late to make their signature seedpods. The next year I gave them a position in full sun, and sure enough they bloomed much earlier - by late August. Which meant that by mid-September, I was admiring the cool immature seedpods, which indeed look like green pufferfish! In our garden the plants don't overwinter – so I have to grow them as annuals.

pufferfish milkweed; balloon cottonbush
Late October – puffering in their prime
Gomphocarpus physocarpus
The aftermath - this photo taken on Christmas day

This plant used to grow in our garden, but it slipped away...

One or more images of this plant are included in my stock photo catalog

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Seed-starting details for this plant

  1. Seed from HPS/MAG '08/'09 exchange. Baggy 70F (40%G, 5-12d)
  2. Same seed as above. Baggy 70F (65%G, 5-10d)
  3. Seed from '10 garden. Baggy 70F (no G, 17d)
  4. Seed from HPS/MAG '08/'09 exchange. Baggy 70F (72%G, 5-10d)

Seed is apparently long-lived, if it is viable in the first place. My own plants seem to not have set viable seed in 2010.

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