We have grown to love monarch butterflies, with their striking orange and black markings and their fascinating annual migration from southern Canada 3,000 miles south to Mexico. To help them, we have increasingly planted milkweed, the only plant on which their caterpillars will feed. In northwest Florida, the milkweed species most planted has been tropical milkweed, Asclepias curassavica, as it is lush, showy and easy to grow.
Tropical milkweed, unlike our native milkweeds that die back in late fall, will continue to grow through the winter unless killed by a hard freeze. Even if the cold kills the stems, it may regrow quickly from the roots. This seems like an advantage, but maybe not. The availability of a host plant for the caterpillars may be prompting adult females to stay and lay eggs rather than migrate south and be protected from deadly freezes.
Experts are also exploring links between the longer persistence of the tropical milkweed into winter and a build-up on those plants of a serious parasite Ophryocystis elektroscirrha, commonly referred to as OE.
So, what is the answer?
- Cut back any tropical milkweed to the ground at Thanksgiving. That may encourage female monarchs to migrate and prevent a deadly build-up of OE spores on the plants.
- Consider adding some native milkweed species to your butterfly garden. Here are some recommended species from Dr. Jaret Daniels:
- Aquatic Milkweed (Asclepias perennis)
- Swamp Milkweed (Asclepias incarnata)
- Pinewoods Milkweed (Asclepias humistrata)
- Redring Milkweed (Asclepias variegata)
For more information: