Gomphocarpus Growing Guide


Common Name Hairy Balls, Balloon Plant, Cottonbush
Genus  Gomphocarpus 
Species G. physocarpus 
Family Apocynaceae
Life Cycle  Tender Perennial in zones 8-10 (grown as an annual in cooler climates)
Tray Size  125
Plug Care Plant immediately after hardening off to avoid rootbound plugs. These are fast growing plants so don't hold them in their plug trays for more than a week after receiving them. Be gentle when handling roots to prevent damage, extreme root disturbance while transplanting can set the seedlings back (Milkweed, in general, do not like root disturbances). 
Netting / Staking These plants get very tall, but the stems and roots are strong and can generally grow unsupported. Space them properly to allow for healthy growth - if crowded they may grow weak and top-heavy which will put them at risk of toppling in the wind. 
Temperature Range Prefers warm temperatures (70-85°F). Not frost-tolerant; wait until all danger of frost has passed before planting outdoors in the spring. Plan to grow them as an annual in zones below USDA zone 8.
Spacing For pinched plants, 24 inches apart is ideal to allow room for branching. Unpinched plants can be spaced closely together (6-12 inches) and each plant will be harvested as a single stem. 
Soil Preference Gomphocarpus thrives in well-drained, nutrient-rich soil with a neutral pH. Avoid overly wet conditions, which can cause root rot. Irrigate and fertilize regularly through the growing season for the best quality cut stems late summer/early fall. 
Day Length Short-day plants; plants require 12 hour days to flower. They will stay vegetative until the days are short enough to initiate flower. Pods develop quickly after flowering. Plant in FULL SUN.
Pinching I prefer to pinch once, at the 5th or 6th set of leaves to encourage multiple side branches to grow. You can also choose to not pinch and plant your plugs more closely together. 
When to Plant Plant after the last frost date for your area. Warm soil temperatures are essential for optimal growth.
Harvesting Harvest when the seed pods are fully developed but still green and firm. Avoid waiting too long, as pods may burst and lose their visual appeal. They develop red coloration on the pod when they are close to bursting. 
Post Harvest Care Cut stems should be immediately placed into cool water. Be careful if you have a sensitivity to plant sap as these milkweed have the typical sap that the plants are named after. Allow them to condition in the cooler before using. 
Diseases / Insects These plants are quite pest and disease resistant. Avoid overwatering as this can cause root rot. Watch for typical milkweed pests, such as aphids. 
Bailey's Notes

These plants make quite the statement in the field and in arrangements. Although they might look odd in a mixed bouquet, they are incredible additions to installations and event arrangements. I prefer to remove all the leaves on the stem to allow the pods to really shine. Pair with emerald tassel amaranth for an out-of-this-world look. 

An interesting observation with this species is that it can act as a host plant for Monarch butterflies. Although it is out of the native range of Monarchs, you might find caterpillars nibbling away on the leaves, and the caterpillars can successfully grow to maturity on Gomphocarpus. 
Resources  Takii Culture Sheet