Mid- to late-June is when the endangered purple milkweed (Asclepias purpurascens) is in full flower. This savanna indicator has responded well to restoration work at Pleasant Valley Conservancy and has become one of our signature species.
Last Thursday, Kathie, Susan, and I did our annual monitoring. All plants are permanently marked and have been under study for a number of years. We now have 20 sites where purples have arisen spontaneously and 14 sites where greenhouse-raised transplants are established. Each site has one or more stems, in some cases more than a dozen. This year 85% of the stems had flowering umbels, which is typical.
Last year we had similar success, but the great drought started in mid June and all the purples collapsed. We did not get a single successful seed pod. Happily, this year's observations show that there was no permanent damage. Hopefully the good rains now occurring will be beneficial and we will get excellent pollination and some seed pods.
Although I have seen purple milkweeds at other preserves in open prairies, at PVC all of our sites are in areas with partially closed canopies (average about 50% canopy cover). We have good populations in both white oak, bur oak and Hill's oak savannas.
We saw our first purple milkweed flowers in 1999, in a small savanna area that had just been cleared and burned. Purples are still flourishing at this site today.
Although purples are not common in Wisconsin, they are surprisingly easy to raise from seeds. Seed germination is very high (in our hands >90%), and seedlings can be easily raised in either a greenhouse or under lights. Details of purple milkweed culture can be found in the paper I published in Ecological Restoration. Download this paper (PDF) published in 2009.
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