Frost damage to plants from recent cold snap

Folks who have lived in Wisconsin a long time are aware that you can't plant tender plants before May 15. But how about the native plants that thrive in our prairies and savannas? One might think that evolution has made sure that they don't start growing too early.

Last Saturday night the temperature dropped below freezing at Pleasant Valley Conservancy. Many species seemed not to notice, including some that were flowering well, such as golden Alexanders, blue-eyed grass, Robin's fleabane, columbine, and shooting star.

However, tick trefoil (Desmodium glutinosum), which was in full leaf, suffered severe frost damage. This was surprising, as this plant was not growing in the bottom land, where frosts usually accumulate, but in our upland savannas. As the photo shows, its leaves really got zapped.

Since we have a lot more tick trefoil than we really need, we aren't concerned about losing some, although it seems likely that the plants themselves were not killed.

Another species that showed frost damage was smooth sumac (Rhus glabra). Most of the stems of this species had been top-killed by our recent controlled burns, but resprouts were just coming up and were damaged.

I haven't done a survey to see what other species might have been affected. Those mentioned were observed during a round of spraying of bramble resprouts.