Like all members of the milkweed family, balloon plant (Gomphocarpus physocarpus) is one of the best plants for attracting monarch butterflies. This unique shrub, which reaches heights of 4 to 6 feet (1-2 m.), is also known by a long list of alternate names including balloon cotton bush, family jewels, Oscar milkweed, goose plant, and swan plant to name just a few.
Let’s learn more about adding this plant to your garden.
Balloon Plants for Caterpillars
Balloon plant milkweed is a unique, vase-shaped shrub that produces light green, lance-shaped leaves and clusters of small, waxy flowers that show up in summer. The blooms are followed by round, balloon-like fruit covered with small bristles.
Balloon plant milkweed isn’t particularly showy, but butterflies love the nectar-rich blooms. In fact, the plant is definitely one of the best plants for attracting monarch butterflies. It is also beneficial because it’s viable later in the season than other milkweed varieties, providing a place for monarch butterflies to lay their eggs before fall.
Native to southern Africa, this milkweed species is suitable for growing in USDA plant hardiness zones 8 through 10. It is fast growing and often grown as an annual in cooler climates. It can become weedy in tropical climates.
How to Grow Balloon Plants
Balloon plant milkweed is most often grown from seed, which can be purchased online or from a nursery specializing in exotic plants or butterfly gardens. It’s also possible to purchase small plants. If you have access to an established plant, you can harvest the seeds in autumn. Let the seed pod dry, then just before the pods are ready to burst, break one open and collect the seeds.
If you’re concerned that the pods might burst, cut a few stems and place them in a jar of water until the pods dry. Allow the seeds to dry completely, then soak them overnight when you’re ready to plant.
In warm climates, the milkweed seeds can be planted directly in the garden, but gardeners in northern climates may want to get an earlier start by planting seeds indoors a couple of months before the last expected frost in your area.
You may need a heat mat, as balloon plant milkweed seeds germinate best in temperatures between 68-80 F. (20-27 C.). Be sure to plant at least two plants, as this plant isn’t self-pollinating. Allow 2 to 3 feet (61-91 cm.) between plants.
Care of balloon plants is minimal as long as you provide conditions they desire. Balloon plant grows best in full sunlight and moist, well-drained soil. It also grows well in large containers.