Grow native milkweed to support monarch butterflies

April 19, 2019

By Molly Jameson, UF/IFAS

With spring upon us, the mighty monarch butterflies have begun their long trek to the north from Mexico, looking to time their migration with growth of the milkweed plants in the southeastern United States. Mated monarch females lay hundreds of eggs along their journey, but only two percent of these eggs will survive to become mature caterpillars to carry on the next generation.

Monarch larvae rely exclusively on milkweed for nutrients, so it is of upmost importance that the plants are available to the offspring at the correct time. If the adult monarchs arrive too early, the milkweeds may not have had enough time to grow after late frosts. If they arrive too late, the milkweed vegetation may not support the nutrient needs of the caterpillars. In addition, the milkweeds contain a poisonous toxin, cardiac glycoside, that stays within the caterpillars’ bodies once consumed. This does not harm the larvae, but actually helps them, as it makes the young and adult butterflies taste terrible and makes them poisonous to potential predators.

Swamp milkweed (Asclepias incarnata). Photo courtesy David Cappaert

For these reasons, it is important that we all do our part to support the growth of native milkweed species. Locally, the Monarch Milkweed Initiate at the St. Marks National Wildlife Refuge educates the public about milkweed and monarchs and grows and transplants native milkweed to support the monarchs on their migration.

When planting milkweed, be aware that there is a popular commercialized non-native tropical milkweed species that is not appropriate for the monarchs in our area. This species, Asclepias curassavica, can flower year-round, luring the monarchs to stay and breed in the winter when they should be on their way back to Mexico to escape freezing temperatures. Staying and breeding too long can make the monarchs susceptible to a protozoan parasite, Ophryocystis elektroscirrha (OE for short), that infects the caterpillars when feeding, reducing their lifespan, body mass, mating success rate, and ability to migrate.

Butterflyweed (Asclepias tuberosa) is one the easiest milkweeds to grow. Photo courtesy UF/IFAS

Luckily, there are about 21 native milkweed species in Florida. Many native milkweeds in the Florida Panhandle require specialized care when grown for transplanting, as different species have adapted to a range of habitats. The Asclepias tuberosa, commonly referred to as butterflyweed, is considered easiest to grow as they transplant well and thrive in full sun. Others, such as Asclepias perennis, or aquatic milkweed, and Asclepias incarnata, swamp milkweed, must be grown using trays without drain holes, as their “feet” must be kept wet. The Asclepias humistrata, or sandhill milkweed, requires a drier, heavier soil.