Tropical milkweed (Asclepias curassavica) is hard to miss at garden centers in spring. Bright red and yellow flowers, long blooming season, easy to find. People plant it specifically to help monarch butterflies, which is a good impulse. The problem is that this plant comes from Mexico and Central America, not North Carolina, and its year-round persistence in warm southern climates can work against the monarchs it is meant to help.
NC has four native milkweed species well-suited to coastal plain gardens. They are harder to find at big box stores, but they are the plants monarchs evolved with. Here is what you need to know.
The Problem with Tropical Milkweed
Native milkweed species in NC die back to the ground each winter. That die-back matters for monarchs. Ophryocystis elektroscirrha (OE) is a protozoan parasite that infects monarch butterflies. Caterpillars ingest OE spores while feeding on contaminated leaves. Heavily infected butterflies are physically smaller and have lower flight endurance than healthy individuals. Infection rates are higher in populations that are not migrating.
Tropical milkweed does not die back naturally in Zones 7b through 9b. It keeps growing through most of the winter in coastal NC, which allows OE spores to accumulate on the plant across multiple generations of butterflies. When monarchs breed on the same persistent plants season after season, OE load builds up. Research on monarch populations in California and along the Gulf Coast has documented this connection. The fix is manageable if you are already growing tropical milkweed: cut it to the ground in October and again in January to force dormancy and break the OE cycle. But native milkweed handles this automatically.
There is also evidence that abundant tropical milkweed in warm southern states may delay monarch migration. Monarchs use the die-back of native milkweed as a cue that it is time to move south. When milkweed is still green and flowering in November, some individuals may remain rather than migrate. The evidence here is less definitive than the OE research, but it adds another reason to prefer native species in your garden.
Native Milkweed Species for NC Coastal Plain Gardens
Four species, four different site requirements. At least one will fit your yard.
The most widely available native milkweed and one of the most useful for dry coastal plain gardens. Its deep taproot makes it extremely drought tolerant once established. Orange flowers in early summer. Needs full sun and well-drained to dry soil. Sandy soils are no problem.
Best for wet or consistently moist spots: rain gardens, low areas, pond edges. Pink to mauve flowers attract monarchs and native bees from midsummer into fall. Taller than butterfly weed, typically 3 to 4 feet. Full sun to part shade.
The only native milkweed that tolerates partial shade. White flowers with a purple-pink center appear in late spring. Good for woodland garden edges and spots that get afternoon shade. Prefers well-drained soil. Less commonly available commercially, but worth seeking from a native plant nursery.
Native to the longleaf pine sandhills of the Southeast, including the NC coastal plain. Adapted to extremely dry, sandy, nutrient-poor soils where little else survives. Pink and white flowers on a spreading plant. Difficult to find in nurseries, but the correct species for longleaf savanna restoration and sandhill garden projects.
Matching the Plant to Your Site
The most common mistake with native milkweed is planting the wrong species in the wrong spot. Butterfly weed (Asclepias tuberosa) will rot in heavy clay or consistently wet soil. Swamp milkweed (Asclepias incarnata) will struggle in the dry sandy conditions that butterfly weed thrives in. Site match matters more than species preference.
In Wilmington and across the NC coastal plain, most residential yards have sandy, well-drained soil with full sun exposure. That points to butterfly weed as the default choice. If you have a low area that holds water after rain, swamp milkweed belongs there. If you are working on a sandhill or longleaf savanna restoration site, sandhill milkweed is the ecologically correct species.
All four species die back to the ground by late fall in NC. That is not a problem. It is how they are supposed to work. The die-back breaks the OE cycle the same way it has for monarchs over thousands of years. A bare patch of soil in December means a healthy plant in May.