Plant milkweed in the spring and summer. The best time to plant is when seedlings emerge from their dormant state. If you wait until mid-summer, the seeds might not have matured yet and won’t be able to survive winter dormancy. Most people start out by planting an entire gallon or pail of fresh seeds—usually purchased at a local garden center. Seedlings will sprout within two weeks of germination and can be transplanted into your yard for several months before they develop roots deep enough to withstand cold winters.