The milkweeds—swamp milkweed, common milkweed and butterfly weed—are excellent additions to the native plant garden. But in my opinion, swamp milkweed is the star of the milkweed show. Swamp milkweed (Asclepias incarnata) is a favorite nectar plant of many bees and butterflies. It’s a perfect choice for borders, stream or pond banks, moist areas, and butterfly gardens.
How It Grows
Swamp milkweed is an easy to grow perennial in USDA zones 3 to 7 in medium to wet soils. Although native to swamps and wet meadows, swamp milkweed is also happy in average clay soils as long as it doesn’t dry out completely. Like all milkweeds it prefers full sun, but will grow in part sun.
Swamp milkweed forms clumps, has branching stems, and grows 3-5′ tall. Plants have deep taproots, so don’t try to move it after it’s established. Don’t worry if foliage is slow to emerge in spring—that’s normal.
Swamp Milkweed Flowers and Seeds
I think Swamp milkweed flowers are more attractive than common milkweed flowers, but you can be the judge of that.
Tiny, fragrant, pink to mauve flower clusters bloom in July and August. Five nectar cups on each tiny flower in the umbrel form a crown that results in an intricate pollination process. Within each small cup is an upward curving horn. An insect’s legs go into a slit between the cups and pick up pollen. Sometimes insects are not strong enough to pull their feet out of the slits and become trapped.
Flowers last about a month and are followed within four to six weeks by brown seedpods three to four inches long. The seeds are attached to silky white down. When the pods dry in autumn, they split open to release seeds that float away in the wind on their white parachutes.
Swamp milkweed is not as aggressive as common milkweed, but it can spread. If you don’t want too much swamp milkweed in your garden, rejoice when you see the red milkweed beetle on your plants. The beetles keep the plants from spreading too much by eating some of the flowers and seeds. If the beetles become too prolific, you can knock some into a jar of soapy water.
It’s a good idea to refrain from cutting stems back in fall, because insect larvae overwinter in the stalk. And never use pesticides (not that you would) on your plants.
More About Milkweeds
Here’s wonderful news for gardeners–milkweeds have no serious insect or disease problems and are deer and rabbit resistant! What more could you ask of a plant? But most importantly, all milkweeds are a host plant for the endangered Monarch butterfly.
A host plant provides for every stage of a butterfly’s life cycle—nectar for the butterfly, a place to lay eggs, and leaves for the newly hatched caterpillars to eat. The milkweeds are the only plants Monarchs can use for their lifecycles. Without milkweeds, there would be no Monarchs. Milkweed stems secrete a toxic milky sap when cut, which is why Monarchs chose this as a host plant. Nothing can eat a monarch butterfly or caterpillar without being poisoned!
By the way, fall is the perfect time to plant, so go buy some swamp milkweed and then spend the winter dreaming of the moment when your new plants emerge from the soil in Spring. You will be rewarded when you see those beautiful flower clusters and Monarchs enjoying your plants.