Farm-Generated Fertility: Vermicomposting Horse Manure and Vegetable Wastes

2015 Annual Report for FNC15-988

Project Type: Farmer/Rancher
Funds awarded in 2015: $7,301.00
Projected End Date: 08/15/2017
Grant Recipient: Spirit of Walloon Market Garden
Region: North Central
State: Michigan
Project Coordinator:
Rachel Cross
Spirit of Walloon

Farm-Generated Fertility: Vermicomposting Horse Manure and Vegetable Wastes



This year, we worked to establish our worm houses and create strong colonies. The first week of May, we constructed two 13’x12’ instant garage-type shelters. With their dark-grey covers and large zipper doors, they worked perfectly for a shaded, easily ventilated worm home. We used woven landscape fabric to cover the ground, and built beds out of cinderblocks. Overhead sprinklers were set up and automated to provide moisture. One house hosted a batch-style bed, while the other was used for the wedge system. We added about 4 cubic yards of horse manure to each system.


The worms arrived on May 10th. After an overnight rest to avoid shock, we added them to the manure in the houses. To the batch system, we added 18 pounds of worms. To the wedge, we added 36 pounds, as this system is designed for more frequent feedings. On the 12th, we added about1 cubic yard aged manure to each system, topping off the bin of the batch system and adding a thin layer to the wedge. We also tried putting pea shoot production wastes through the chipper/shredder. However, this, and other vegetable wastes, did not perform as planned when placed in the shredder. We ended up with buckets of wet goop and a clogged machine, rather than spreadable material. In the future, rather than chipping, we simply spread whole vegetable wastes on top of the piles. At this point, a layer of thin straw was spread on both piles to conserve moisture and provide darkness.


We had planned on feeding the wedge worms weekly. However, they did not process material as quickly as we had anticipated, perhaps due to the amount and size of the material added. By mid-June, we were beginning to see results in the wedge pile, with generous amounts of castings on the surface. Both piles hosted eggs and baby worms, so our worms were happily multiplying. On June 16th, we added a fresh layer (about .5 cubic yards) of aged manure to the wedge pile. We also added coffee grounds from a local café, hoping that the extra nutrient boost would speed up material turn-over. On June 30th  we took samples from both piles to run an unplanned germination test with basil, rye, kale, and cucumber seeds.


At this point, we became slightly discouraged with our methods. The germination was excellent (averaging 92% in both samples), but our vegetable seeds were not the plants to emerge. Both of these samples, and all future samples, were contaminated with weed seeds, especially those of a plentiful and pernicious grass. Disheartened, we realized that we would need to first hot-compost the manure to kill the weed seeds, slowing our rate of feeding. Our vermicompost was also turning out to be very sandy, as when the stable owners cleared the manure from the paddocks, they scraped the tractor bucket across the earth. We were realizing that perhaps this manure was not the best feedstock for our worms.


On July 22nd, Dr. John Biernbaum of Michigan State University visited us and inspected our project. He suggested that we pre-compost our feedstocks to diminish our weed problems. Like us, he also noted the sandiness of our compost, and said there was little we could do for that, if we aren’t piling the manure ourselves. He suggested that we cut back on watering (our beds were becoming a little soggy at the bottom), and remove the worms from the batch system, as that pile was close to completion. At his advice, we added several crates filled with fresh material to the top of the batch pile to collect the worms.


On August 3rd, we added more aged manure to our wedge system. This was from a pile that had been hot-composting since spring. We added about 12” of fresh material, along with our batch pile worms. As we utilized less-frequent feedings, and had slow worm population growth, we decided to stretch the compost process for as long as possible. On October 7th, we added another 12” of fresh material. A long, warm fall kept the worms active into the beginning of December.  


On December 10th, we decided to close the project for the winter. We took finished samples from each system, batch and wedge, to submit for soil sampling. We then combined the two piles for the winter, and topped with a thick 2’+ layer of new material, followed by a 2’ layer of straw. In the spring, the worms will be in the new material, which we will remove and use to begin the process once more. The vermicompost we created this year will be utilized in our herb hoop house, after a period of further composting in an effort to destroy the weed seeds present.  



We have learned a lot from this project, as it did not meet our planned expectations. We are seriously reconsidering the use of horse manure as a feedstock for next year; it creates happy worms, but it’s difficult to ensure quality when using. The coffee grounds created really beautiful castings, and we are leaning towards focusing on pre-composted coffee and food wastes for the upcoming season. These materials will also be more appropriate in the wedge system, as horse manure does not lend itself well to being spread in a thin layer.


The houses themselves performed well. They stayed cool and shady all summer, and we did not see any run-off from the piles. The batch system yielded about 4 yards of compost with an input of 5 yards of material. The wedge system yielded about 5 yards with an input of 7.5 yards of material. Our results may be skewed, however, by the presence of sand. As we did not separate the worms completely from either pile, we cannot measure their population increase. However, we observed many worm eggs and small, young worms throughout the season.


The most exciting part of project (besides being the caretakers of thousands of worms) was the fact that the two systems yielded two unique composts. The batch system produced a high carbon, lower nutrient compost. The wedge system produced a compost with 50% more nutrients (N,P,K, Ca, Mg) than the batch system (when compared at equivalent moisture content.) Both composts had pHs in the 6.5-6.6 range; ideal for our soils.



Next year, we will resume the project with a focus on food wastes and the wedge system. We hope that the compost production will be more rapid in the upcoming season. We did not host our field day nor present at the Northern Michigan Small Conference this year, as we did not feel that we had enough solid, usable information to share. Sharing our results with others will be a large part of our plans for 2016. In 2015, we learned what not to do; in 2016, we hope to come full-circle in our project by applying what we learned to create high-value, non-contaminated vermicompost.



As above, we did not host our field day nor present at the Northern Michigan Small Conference this year, as we did not feel that we had enough solid, usable information to share.  However, we did host around 10 curious farmers and community members in informal tours. We also shared pictures and updates on the project in social media. Sharing our results with others will be a large part of our plans for 2016. We are aiming for a field day in July to share our advances in the project.