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.
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.
Watch for germination in two to three weeks. Turn off the propagation mat one week after the seeds sprout. Move the pots into a cold frame outdoors or against a south-facing wall with noonday shade.
Arrange the starter pots on a propagation mat near a source of bright, indirect light such as near a partly shaded south-facing window. Set the temperature on the propagation mat to 86 F during the day. Turn it off at night.
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.
You don’t need to worry about watering or caring for the seeds through the winter. The cold and moisture that naturally come from snow and rain will tell them when to start growing.
The straight species Asclepias tuberosa has brilliant orange blooms. However, there are a few cultivars that range from orange to yellow to red.
How to Grow Butterfly Weed
Whether you started your own seeds or bought transplants, the key to planting butterfly weed is to disturb the roots as little as possible.
The seeds need the cold period of winter in order to germinate in the spring. You can sow them directly into your garden in late fall (usually November).
Once seeds have germinated, you can thin them out to one per pot. Keep pots watered and under fluorescent lighting or somewhere with a good amount of sunlight. You can run a fan for 15 minutes twice a day to make sure they have good airflow.