(Editor's Note: This article was originally published on March 9, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
Plants of the genus Asclepias, the milkweeds, are well known to be attractive to many insects, and the monarch butterfly in particular can not survive without milkweed as its host. Accordingly, it is an essential in any butterfly garden where the monarch has its range. I do not have a butterfly garden, but when a few adventitious common milkweeds, Asclepias syriaca, sprouted along a fence, I did not hesitate to let them grow, for the sake of the butterflies.
This decision proved at first quite rewarding. The milkweed flowered abundantly, and its fragrance was extremely attractive.
I was delighted to see all the different species of bees that came to nectar on the milkweeds, as I am even more fond of bees than of butterflies. When some of the milkweed stalks reached six feet in height and began to topple, I secured them to the fence to keep them from falling over. At the end of the season, I cut the milkweeds back, but I was happy to see them coming up again the next spring. And the spring afterward, even more of them. And the spring after that. Until I reached the point of wondering, maybe the milkweeds have gotten a bit out of hand?
But they had only just gotten started. I started to see milkweeds sprouting in the lawn. The lawnmower cut them down, but only a few days later, they were coming back again. I started to pull up the sprouts, but still they kept returning. The next year, there were even more milkweeds coming up in the lawn, even farther away from the fence where they had originally sprouted. I spent another year cutting and pulling them, without reducing their numbers in the least. The year after that, there were even more milkweeds in the lawn. Reluctantly, I tried spritzing a few of them with herbicide, but the milkweeds scoffed at it.
A few years ago, the fence came down. Unperturbed by the loss of their support, the milkweeds continued to spread across the yard. They were coming up in the lawn all throughout last year, and I expect to see them there this year, too. Because now I know what I did not know at the time I first let it grow, that milkweed is not an annual, dying at the end of a season and coming back only as new seeds sprout. It is an aggressive, tenacious perennial that spreads by deep underground rhizomes. Attempts to dig up or plow under the roots only encourage it to spread even further. Calling this plant a weed was definitely appropriate.
But what about the butterflies, if no one will plant milkweed? There is a happy solution. Asclepias syriaca is only one over a hundred species in the milkweed family, native to the Americas, and they are all quite suitable hosts for butterflies, including the monarchs.
These Asclepias are not only very attractive - and plant breeders have introduced improved cultivars - most of them are smaller and less invasive than the common milkweed, less likely to escape your butterfly garden and march off in search of new lawns to conquer. The different species are also adapted to different habitats, so that you can select a variety that is well suited for conditions in your own garden, or native to your area. For example, while most milkweeds prefer drier conditions, the swamp milkweed, A. incarnata, is adapted to moist soils that may not be so well-drained.
All Asclepias can be propagated from seed and by rooting young shoots. The exact requirements for each species vary. Flowers can be many colors, from white to yellows, oranges and reds, as well as the pink of the common milkweed. But you and the butterflies and the bees will both have fewer regrets if you plant some of the other species.
Photo credits - Bees: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License
Milkweed flower close-up: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License