Hot Box Compost: Modular Composting System that Heats, Waters, and Fertilizes Grow Bed for Off-Season Production

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2021: $13,747.00
Projected End Date: 12/31/2023
Grant Recipient: Low Technology Institute
Region: North Central
State: Wisconsin
Project Coordinator:
Scott Johnson
Low Technology Institute

Information Products


Not commodity specific


  • Crop Production: season extension
  • Soil Management: composting

    Proposal summary:

    Imagine a cube measuring 4 ft on each side. On top of the cube is a rich bed in which edible greens are growing. The soil is watered and fertilized from below, plus carbon dioxide seeps up from the soil. The soil is warm, even though this box is in an uninsulated greenhouse. Inside the box is a cubic yard of compost, waiting for use in the spring. This is the central idea of hot box composting.

    Although compost-heated greenhouses are nothing new, they require dedicated infrastructure and space in a greenhouse. This project seeks to test a scalable, modular, and mobile composting box that any market gardener could build to grow greens during the shoulder and off seasons, when these products fetch a higher price.

    The project will run a series of controlled tests to determine the best practices with this system, including determining the optimum aeration of the compost; ideal carbon-to-nitrogen ratio, moisture content, and free air space in compost inputs; measuring nitrite and nitrate outputs; how to best control moisture, heat, and carbon dioxide output; and best crops to use based on available resources.

    Project objectives from proposal:

    1. Build twelve hot box composting units and evaluate the optimum configuration of variables of over the spring and summer of 2021.

    2. Test six units each at two hoop-house locations over the winter of 2021–22 and evaluate performance through qualitative and quantitative recording.

    3. Disseminate findings through field days, presentations to industry groups, write-ups in popular and technical publications, and digital podcasts and videos.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.