Culture
Winter hardy to USDA Zones 8-10. Invasive self-seeder in tropical areas (it has naturalized as a pasture weed in Hawaii), but not in St. Louis where it is grown as an annual. Best in well-drained soils in full sun. Plants are drought tolerant. Seed may be started indoors in pots 6-8 weeks before last spring frost date.
Noteworthy Characteristics
Gomphocarpus physocarpus, commonly called balloon plant, is native to southeast Africa. It is an upright shrubby perennial that typically grows to 4-6' tall on stems clad with lanceolate green leaves (to 4" long). This milkweed family member is perhaps best noted for its soft, spherical, balloon-like, spiny, lime-green seed pods. Pods ripen to tan before splitting open in fall to release large numbers of silky-haired seeds to the wind. White flowers in drooping clusters are not particularly showy. This plant is commonly sold in commerce by its original name of Asclepias physocarpus.
Genus name comes from the Greek words gomphos meaning bolt or nail and karpos meaning fruit.
Specific epithet from Greek means bladder (physo) and fruit (karpos).
Problems
No serious insect or disease problems.
Uses
Unique seed pods add interest to garden areas. Stems with seed pods make excellent additions to dried flower arrangements.