I appreciate that people are trying to plant native milkweed to help the struggling monarch population. Unfortunately, native milkweed species are difficult to find and even more difficult to grow. The only commercially available species are Asclepias fascicularis and Asclepias speciosa, both of which the Botanic Garden tries to have for their fall sale. The remaining species require specific growing conditions to thrive and can only be purchased as seed.
Here at Terra Sol Garden Center, we organically grow tropical milkweed (Asclepias curassavica) from seed. We only have it available during the spring and summer, and we encourage customers to cut it down to the ground in winter. Tropical milkweed is not a threat to monarchs so long as the people growing it are responsible and well informed.