Grow Perennial Milkweed to SAVE the Endangered Monarch Butterfly. Monarch numbers and milkweed plants are down 90% from what they were. Milkweed plants are the only source of food for the monarch caterpillar. Make a difference by planting milkweed! We offer four varieties including Milkweed, Butterfly (Tuberosa), Milkweed, Common (Syriaca), Milkweed, Swamp (Incarnata), Milkweed, Showy (Speciosa) so you can choose and grow the best milkweed for your region! Asclepias plants and sap may cause skin irritation in humans and animals. Do not ingest seed or plants.