Testing the Compost-Heated Greenhouse in an Urban Setting

Project Overview

Project Type: Farmer
Funds awarded in 2012: $5,042.00
Projected End Date: 12/31/2014
Region: Northeast
State: New York
Project Leader:
Jesica Clark
South Pine Street City Farm

Annual Reports


  • Vegetables: carrots, greens (leafy), radishes (culinary)


  • Crop Production: municipal wastes
  • Energy: energy conservation/efficiency
  • Soil Management: organic matter
  • Sustainable Communities: urban agriculture

    Proposal summary:

    The South Pine Street City Farm has established productive vegetable beds and a perennial garden to promote insect diversity. Our new greenhouse will be used to supply seedlings for the farm, other community garden efforts in the city and possibly produce greens in the winter for market.

    This project will convert the method of a compost-heated greenhouse to an urban setting by taking advantage of free materials produced in the waste stream of the city and using them as the basis of different compost mixtures to directly heat the planting substrate and the surrounding air in a small greenhouse. We will test three different mixtures over three time periods and for two greenhouse purposes: winter vegetable growing and seedling production. During the project we will test the heat production of the compost as well as the production of carbon dioxide (CO2) and ammonia. If the project is successful we will reduce the amount of waste produced by the city and provide new methods for increasing the efficiency and market diversity of urban farms. We will also provide a new way for urban farmers to collaborate and form partnerships with other businesses and with their municipality.

    The data that I will collect during our project will be presented to other farmers, especially urban farmers in other cities throughout the Northeast. If our project is successful, we will encourage other farms to install compost heated greenhouses and provide instruction and technical tips online. Because we are located in a city, we are in a highly accessible location for visits to see the process and we have willing educators that can explain the project and its outcomes to visitors.

    Project objectives from proposal:

    The practice of urban farming has increased dramatically as an offshoot of the growing local and organic movements. The success of these ventures depends upon the ability of the farms to be able to close loops in their production and use materials efficiently. A compost heated greenhouse may cut down fuel usage, remove waste from the city and create usable compost. We seek SARE funding to revise and add this technology to the toolbox of urban farmers by converting a greenhouse to hold several cubic yards of compost, creating three different mixes of coffee grounds and carbon rich yard waste and testing the ability of these mixes to heat seedling trays and soil while monitoring the production of metabolic gasses.

    Our situation provides an opportunity to translate and refine the idea of a compost heated greenhouse to an urban setting. In the past, the feasibility and efficacy of compost heated greenhouses were tested using animal manures and medium to large scale composting operations (AttraCT137). Although the results of these studies were mixed, the practice has continued and has had anecdotal success. In the city, access to animal manure is limited and pricey to have trucked in, but other organic materials such as used coffee grounds, dried leaves and chipped branches are in good supply and free to use. The advantage of these materials is that they are usually consistent in their make-up and can be mixed in a relatively precise ratio to maximize heat production and perhaps regulate carbon dioxide and ammonia production. Collecting the materials separately lets us mix them in different ways to also maximize their composting rate and heat production. They are also high in nutrients and should provide a quality finished compost, another product that is in high demand in urban agriculture. Lastly, these ingredients have the side benefit of being less offensive to the public than manure, an important factor in a crowded city.

    In the fall of 2012 we will begin by constructing compost bins out of cinder block to hold the compost over the winter and spring. We will consult with Cornell Cooperative Extension (CCE) on the design of these bins to maximize their efficiency and heat producing potential. Directly on top of the bins we will lay simple benches made of lumber and welded wire fencing to hold trays of seedlings. For winter production we will remove the tables, put down a layer of heavy duty landscape fabric and add an extra layer of block on the walls to hold soil and grow directly on top of the composting materials.

    Over the run of the project we will use three different mixtures of coffee grounds to yard waste to gauge their effectiveness in heating the greenhouse. The first mixture will be comprised of coffee grounds and dry leaves. The second mixture will be coffee grounds and chipped wood. The third mixture will be grounds, leaves and chipped wood altogether. We will consult with CCE on the proper ratio of these ingredients in the mixture.

    As the greenhouse and bins are worked on, we will begin collecting used grounds from local coffee businesses in our city. We must begin early so that we have enough collected by the time the construction is finished. The collected materials will be held at our farm until they are needed. The businesses will be given six to seven 5-gallon buckets each and three buckets will be collected every few days so they do not pile up at the businesses. Coffeehouses are willing to donate their used grounds because otherwise they would have to throw them out, which is a messy, heavy and sometimes expensive procedure. Yard waste in the form of leaves and chipped branches is freely given by the city to reduce waste buildup at the transfer station. We will collect these materials when we are filling the greenhouse bins.

    By late fall, we will fill one row of bins with our three mixtures, separated by the walls of the bins. As we fill, I will measure the weight of each type of material and also note how long it took to fill the bins and how hard the process was on the farmer and workers. In this first filled row we will grow our winter produce in soil fill on top of the compost, but separated by landscape cloth to maximize heat transfer while keeping the materials separate. Because we are in the northeast, I expect to be able to grow hardy produce such as arugula, lettuce and baby kale for our winter production, or perhaps extend the season of plants such as chard, fennel and artichokes.

    In the early winter before the ground freezes, the other row will be filled with the three mixtures in the same way as in the fall. We are filling this row later so that it will still be active as we begin to grow our seedlings. In the late winter, we will use this second row for seedling production, starting with brassicas, onions, etc.

    Sometime in the late winter or early spring, as our outdoor piles of yard waste and coffee grounds thaw, we will replace the filling in the winter production bins with new composting materials, in the same three mixtures, thus expanding our seedling production space to include warm weather crops such as tomatoes and cucumbers. In this way we will have tested the effectiveness of the three different mixtures over three different time periods. The partly finished compost from the first row’s winter production will be transferred to another area of the farm to complete the process and then be used by the farm as an addition to the beds, or as a component in the greenhouse soil medium. As this compost from the greenhouse bins is finished, we will test it using a soil lab and analyze it with the help of CCE. Throughout the project I will be monitoring temperatures and levels of CO2 and ammonia as outlined in Question 5.
    Finally, after we have collected for both the winter and spring production, I will conduct a survey with the participating businesses and municipal workers to observe their experience in participating in this project and to gauge their willingness to continue cooperating with our farm. In a city setting it is important to build these relationships, correct any negative feedback and reinforce any positive responses.

    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.