Seeds from this butterfly plant Silky Scarlet Asclepias Curassavicai. They blossom in zones 4 to 11 throughout the season and will bring more butterflies than you can imagine. These plants are perennials and grow in full sun and sandy soil is best for them. Quite a drought tolerant plants and is a real attraction to the garden with its bright golden blossoms, We recommend that tropical milkweed, which can be generally called Asclepias curassavica, should be cut back in the winter and fall months in the southern U.S. and California.