1. The most practical way to propagate Asclepias is from seed. Use dry, not fresh seed. Like many wind-distributed seeds, milkweed’s needs to dry before being sown.
2. The seed needs to undergo a period of cold, damp conditions before it can germinate. Sow seed in late fall or winter, and keep it cold and slightly moist for six to eight weeks before allowing it to warm up again. This is best accomplished by leaving the pots in a sheltered outdoor location, such as a cold frame. Failing that, the pots may be held in a refrigerator for their chilling period and then returned to room temperature. Extra heat is not recommended.
3. Seedlings may be pricked out when they have two to three sets of true leaves, then grown on in individual pots until they are sturdy enough to be set out in the garden. Avoid breaking the taproots; milkweeds do not recover easily from root damage.