It is a bit unfortunate that one of the best native plants for Catskill gardeners, Asclepias incarnata, should have been given the name “swamp milkweed.” I just tried to give away a couple of seedlings of swamp milkweed, and I was greeted with suspicion. “Weed? Is the plant ugly?” “No, it’s quite pretty.” “Do I need to put it in a swamp?” “No, any garden spot that is not dry will do. I have mine growing in a raised bed, which is never watered, and it does very well.” “Are you sure this is not a weed?” “It’s nice, I promise.”
In the field the best way to determine if you are dealing with a milkweed is to detach part of a leaf, which will expose the milky sap. Milkweeds also have distinctive flowers, and among milkweeds Asclepias incarnata is generally easy to recognize: the strong, straight stems, sword-shaped leaves, and purple flowers held upright at the top of the plant.
There are several reasons why Asclepias incarnata is such a superb plant for the Catskills. First of all, its flowers: on mature (3-year-old) plants, fist-sized clusters of purple flowers are held near the top of the plant for five solid weeks from the end of June into August. This happens to be the time of year when most gardens have gone quite green: all the spring blooms are done, but none of the late-summer bloomers (asters/sunflowers/goldenrods/rudbeckias etc.) have begun. Swamp milkweed provides superb color at that time. And the flower color – a light purple – seems to mesh well with most other garden colors (there is a white cultivar called “Ice Princess,” also very nice).
The plant is also extremely well-behaved for garden purposes. Unlike most other Asclepias species, A. incarnata grows wells in containers and is available at good nurseries. It grows reliably in a clump and sends out no runners (unlike common milkweed, Asclepias syriaca, which is very difficult to control). I have found that it does seed in to my garden but only a few individuals come up every year – just enough to share with friends. Unwanted seedlings are easily removed. The plant is not difficult to grow and does not, I repeat, does not require swampy conditions. An average garden soil in the Catskills will suffice, and while it prefers sun, it will grow and flower in part sun or part shade as well.
Best and perhaps most important of all, Asclepias incarnata is in the dogbane family (Apocynaceae), which along with the iris family (Iridaceae) offers the best deer resistance of any of the herbaceous plant families. In a year when I was absent from my house for months at a time and deer destroyed many of my typically unpalatable plants (mints, Coreopsis, St. John’s wort), I found they did not even touch my irises, bluestars (dogbane family again), or milkweeds.
The final reason to grow Asclepias incarnata is that it is one of the best pollinator species available. Every day it is in bloom, a little army of bees, butterflies, and other small insects is found crawling over its fragrant, nectar-bearing flowers. At at time when deer and pesticides are destroying many of the flowering plants of the understory, a stand of swamp milkweed is a valuable food source for local pollinators. And like all Asclepias species, swamp milkweed is a host plant for the monarch butterfly (Danaus plexippus), a once-common species currently undergoing a population collapse. I have six nearly-adult monarch butterfly caterpillars on my milkweeds this year, and five of six of them are on my Asclepias incarnata (I also have A. tuberosa and A. syriaca on my property). These caterpillars, if they are lucky and can make it, will follow the goldenrod and aster blooms down south all the way to Mexico, where they will spend the winter and become the parents of the next year’s monarchs.
Asclepias incarnata is listed as occurring in all the Catskill counties, though I have never seen any in the wild. If anyone knows where some are, tell us, because it’d be nice to find and propagate the local genotype.
What we can do for the monarch. The health of the monarch population depends on many many factors, because their habitat is basically a chain stretched across all of North America, and any break anywhere in the chain is a threat. It is easy to be pessimistic about our ability to help the monarch, but the mere fact that my property has become a nursery for monarch caterpillars, when it was not five years ago, shows that individuals can make their own small contributions. If this is true even in the upper Catskills – not the most important flyway for monarchs – imagine what a difference a gardener can make further south. It appears that Asclepias populations are particularly low in the Mississippi Valley south of Memphis, so if you know any gardeners in that area, encourage them to plant milkweeds. On a recent bike trip, with the help of local Catskill butterfly guru Maraleen Manos-Jones (whose website is well worth visiting), I had Asclepias seeds with me and gave them to people and planted many myself, all through Louisiana and Mississippi and Tennessee and Arkansas. Monarchwatch.org has been giving out free milkweeds for people to plant, and Catskill Native Nursery has been selling milkweed plugs below cost in an effort to be part of the solution. Human transformation of the North American continent is almost certainly the reason why monarch populations are declining, and hence it stands to reason that human beings can be part of their regeneration as well. In fact there is some evidence that the monarchs are experiencing an uptick in population this year, perhaps as a result of human effort.