Tom's Blog

Friday, June 15, 2012

Sweet clover time

Sweet clover (Melilotus) is the bane of many prairie restorations. Here are some reasons:
  • The seed bank lasts a long time (>75 years)
  • Fire stimulates seed germination
  • It will invade and overshadow native prairie plants
  • It is hard to spray without affecting native plants
  • It can be mowed but timing is critical. It has to be in flower so that the mowed stump won't resprout, but if mowing is delayed too long seed set may have already occurred.
  • Hand pulling is the method of choice, but this is laborous and time-consuming, and generally comes at the hottest time of the summer.
  • Pulled plants that have already flowered may go on to make seed and hence must be bagged, an awkward procedure.
A good rain makes hand pulling lots easier, but if the plants are already flowering you can't wait for rain. We seem to be in a drought right now and who knows when it will really rain?

Small plants can be hand pulled now (with difficulty) but for large plants, especially multi-stemmed ones, a shovel must be used. The ideal shovel is a Parsnip Predator, sold by the Prairie Enthusiasts. The photos here are of a home-made version. The shape of the blade is critical. The goal is to cut the root of the sweet clover plant far enough below ground so that the plant will not resprout. Once the plant is cut, the whole plant is removed (and bagged if there is danger of seed maturation). With the narrow profile of this shovel you can get the tip below ground where it will cut the root. At the same time, nearby native plants are not disturbed. Also, the wide top part of the shovel is needed for the foot.

Although we have sweet clover at Pleasant Valley Conservancy, it is minor in comparison to that of Black Earth Rettenmund Prairie. Therefore, our regular crew plus interns have been working there at least two days a week. Lots of stoop labor!

Once the major infestations have been dealt with, we will continue doing sweet clover at BE until early fall, since scattered plants keep coming up all summer, and there is also fall regrowth. Although these late-arriving plants are small (and hence difficult to find), they generally flower and make at least a few seeds. Our goal is to keep any new seed formation from occurring.


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