Place the butterfly weed seeds in a plastic bag filled with 1 cup of moistened perlite. Store the bag inside the refrigerator for three months. Mist the perlite with water every few days to keep it from drying out completely.
Transplant the butterfly weed into a permanent bed in spring just after the last frost. If planting butterfly weed in clay soil, dig in 2 to 4 inches of compost to lighten the soil, or consider building raised beds to increase drainage.
Butterfly weed and milkweed seed pods may be harvested and planted to support Monarch butterfly caterpillars. Butterfly weed grows well from seeds, which must be harvested in late summer and either sown immediately in the garden, or started in spring after a lengthy chilling process. The seeds are viable and will germinate with little care, although they must be planted at the appropriate depth to ensure successful sprouting.
Snip off the pod using pruning shears. Slice lengthwise along the edge using a utility knife. Pry open the seed pods. Scoop out the seeds and fluffy matter inside and place it in a bucket.
Gather the butterfly weed seeds in late summer or autumn, once the pods dry to a light, rosy-beige color, but before they split open. Put on rubber gloves before handling the pods to protect your hands from the mildly toxic sap.
Harvest the seed pods of butterfly weed when the pods begin to split. Seeds can be sown directly outdoors in late fall or started indoors.
When sowing seeds outdoors, work up the soil in a protected location in early to mid-November. Scatter the seeds over the prepared seed bed and then cover the seeds with approximately 1/4 inch of soil. The cold, moist conditions over winter improve seed germination. Seedlings should emerge in spring. Carefully transplant the seedlings to their permanent locations when the seedlings are 3 to 4 inches tall.
To start seeds indoors, fill a flat with a commercial germination medium (such as Jiffy Mix). Moisten the medium. Scatter the seeds over the surface of the germination medium and lightly press the seeds into the material. Cover the seeds with an additional 1/4 inch of the germination mix. Carefully moisten the additional material. Slide the flat in a plastic bag and place the bagged flat in the refrigerator. Leave the flat in the refrigerator for 4 to 6 weeks. After 4 to 6 weeks, remove the flat from the refrigerator and place it in an area with a temperature of 70 to 75 degrees Fahrenheit. Seeds should begin to germinate in 3 to 4 weeks. (If no seedlings appear after 4 weeks, place the flat back in the refrigerator for another 4 to 6 weeks and repeat the process.) Take the flat out of the plastic bag as soon as seedlings appear and place the flat under fluorescent lights in a 60 to 65 degree Fahrenheit location. Transplant the seedlings into individual pots when the seedlings are 1 to 2 inches tall. Continue to grow the seedlings indoors under fluorescent lights for several more weeks. Prior to planting outdoors, place the seedlings outdoors in a shady, protected location and then gradually expose the seedlings to longer periods of direct sun. Plant the seedlings in their permanent locations after they have hardened outdoors for 10 to 14 days.