stilt grass composting

Asked September 23, 2020, 1:37 PM EDT

Several citizen groups have recently asked me if the Montgomery County and Prince George's County composting facilities get hot enough to kill Japanese Stilt grass seeds. I'm waiting for a response from those locations. Do you have any information on how hot composting must get to kill the seeds of stilt grass? Sincerely, Aubin

Montgomery County Maryland

1 Response

Hello Aubin,

We had a similar question recently from another municipal composting center. Here is what we could find regarding Stiltgrass seed survival in industrial-grade composting:

This is a very valid concern to have though of, though unfortunately we do not have scientific data on this to say if this degree of composting will be sufficient to kill Stiltgrass seeds; more research probably still needs to be done. One of our Extension weed specialists presumes that composting will work, but success will be dependent on time involved, and three days may not be enough. (We don't know exactly how long would be sufficient, but this article suggests it could take upwards of 30 days for hard-to-kill species:

The composter can perform a test if the logistics of this are attainable: put some viable Stiltgrass seeds in a fine mesh bag (so it breathes and maintains the temperature of its surroundings), and let this compost with the rest of the pile. (We realize the piles they are working with may be too large to make this practical, since finding the bag after the pile is turned repeatedly will be challenging.) Remove some seeds after various lengths of time and test if they germinate. A possible complicating factor is that the seeds might need vernalization (cold exposure, such as from weeks of winter) first in order respond, even if they are viable to begin with.

Another potential problem arises from storage of the finished compost. If it is kept in an open location (rather than stored bagged), seed from Stiltgrass and other weed species in adjacent wild areas may contaminate the pile, even if original seed in the pile was killed.