I Want to Kill the Seeds of Russian Thistle and then Compost It
Question
September 10, 2024
I have been pulling up a lot of Russian Thistle from my yard and I want to compost it. Rather than just add it to my compost pile I want to “bake” it first to kill the seeds. I put down a black tarp and put the weeds on top of that and covered with a clear tarp. However, the temperature does not seem to be getting to the 130-150 F range. I have thought about creating a “solar oven” which is what the tarps are supposed to simulate. Maybe I need to create something more oven-like. Do you have recommendations on how to do this? Any publications you can point me to? FYI, I am a Santa Fe Master Gardener and plan to take the Composting class when it is available. Thanks for any information you can provide.
Answer(s)
Answer by JZ: Great idea to capture that organic material from thistle! Here are my thoughts: I think that you are following the temperature guidelines for hot process composting. You could continue to do what you are doing, just give it plenty of time, then the seeds will eventually liquify - be patient. Some composters put weeds in black plastic bag, tie it shut, then put in sun till the contents liquify - this would an anaerobic process. Your heat issue might be that your setup is horizontal rather than conical, so it is not “holding" in the generated heat from the breakdown of carbohydrates. If horizontal on the soil surface, then when ambient air temp drops at night, some of the generated heat will easily dissipate due to upward loss. And you might be creating a low oxygen environment with your current setup which may not benefit the dynamic hot process. If you were to make a conical pile with the thistle, then the core temp might be better kept within the pile. Would suggest that you add some coarse bulking material as you build the pile to allow for convective airflow. Then turn that pile every 2 weeks so that all the material is exposed to the high core temp then any seeds would be destroyed. Continue to cover the top of the pile with a tarp to preserve moisture. You might enjoy reading pp.5-7 of this brochure:
https://www.nmcomposters.org/_files/ugd/9ed432_2efaef3fb0404de2b74b646940ed51ac.pdf
Hope this helps. Get back if you have questions.