Unfinshed Horse compost

Asked May 3, 2020, 12:00 PM EDT

My son brought me a yard of what was advertised as horse compost. It would be considered aged manure as it was spread on the ground last summer, and then scooped up in a heap over the winter in a 30 ft pile. He said it was steaming as they loaded it. IHowever I think it maybe described as unfinished compost as there is a faint manure smell. and it does not look dark like soil. I am concerned about weed seeds. Does it sound sufficient to sterilize the seeds? Should I put it in a compost bed to allow it to finish composting? I have raised beds that normally require little weeding. Would mulching over it with bark chips work to keep seeds from sprouting if there are some? Thank you.

Kent County Michigan

1 Response

Hello and thank you for using eXtension for your ask an expert question. Manures make great compost additives to your gardens. You are correct in that it looks to be unfinished compost. Heaping manure into a pile is not composting. Its heaping. Composting involves actively turning the materials to get a uniform decomposed product. This did not occur. It especially true if the materials still smell of their original source.

Fully composted materials including manures should smell like loam or soil - not manure. I recommend piling or binning your load to make a minimum size of 3x3x3 to get hot compost conditions. Hot compost will kill pathogens and most weed seeds. Turn your compost every week for 4-6 weeks. If you don’t have a compost thermometer, I suggest putting your hand into the center of the pile every week to feel if it is heating. Let it rest for two more weeks. It should be smaller and not hot in the center and smell of loam or soil.

Then, because it is manure based mix it with soil before applying or apply very thinly leaving space around your plants so it won’t burn them. Composted manures should be applied at about a 1:8 ratio of manure to soil to avoid plant burn. Here are some websites for more information about composting at home. http://cwmi.css.cornell.edu/smallscale.htm and https://www.epa.gov/recycle/composting-home