Growing On and Under Asphalt

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2010: $3,835.30
Projected End Date: 12/31/2013
Region: North Central
State: Missouri
Project Coordinator:
Robert Wright
Conception Community Farm

Annual Reports


  • Animals: poultry
  • Animal Products: eggs


  • Crop Production: municipal wastes
  • Education and Training: demonstration, display, on-farm/ranch research
  • Farm Business Management: feasibility study
  • Production Systems: organic agriculture
  • Soil Management: organic matter
  • Sustainable Communities: urban agriculture

    Proposal summary:

    The problem that we have is that half of the soil that we have to grow in is currently covered by three inches of asphalt and five inches of gravel. Below that, the soil is extremely compacted and lacking in organic matter. So how do we restore this space to a beautiful productive farm? And how do we do it affordably and sustainably?

    A lot of urban farms and gardens promote building raised beds right on top of the parking lots. Some use containers; some just spread 18 inches of soil and plant right into that. Both of these methods are very quick to construct, and if you are bringing in organically enriched soil, the methods can produce good yields in the first couple of years. The problem with this is that these methods are extremely expensive and unsustainable.

    We recently looked into a local organization in our city that builds beds like the ones described above. We found that to build 40 growing beds at 100 sq ft apiece, with a soil depth of 18 inches will cost $19,200. And that is just for the materials. Our farm would like to eventually max out at 100 100-sq-ft beds. If we were to develop all of those beds at once we would be spending close to $48,000. And with the additional cost of land, water, seed stock, inputs, and food storage, the possibility of urban agriculture being a viable way to make a living becomes bleak.

    In addition to the cost in monetary resources we believe that building beds on top of the asphalt is also environmentally unsustainable. When raised beds are constructed out of timber, the borders rot over time and have to be replaced. This process often occurs faster than the process of producing new trees to replace the lumber. Furthermore how hard is it to keep 18 inches of soil from washing off of asphalt? It's a battle not worth fighting, so every year new material has to be brought in from off the farm to replace the soil lost from erosion. What the above methods are teaching is that soil can be constantly brought in from off the farm to replace soil loss. What we need to be teaching and learning is how to restore damaged soil and how to build new soil.

    Conception Community Farm wants to teach and demonstrate to our community and region that soil can be maintained and created on site through sustainable agricultural practices. We also want to demonstrate that starting an urban farm can be affordable for everyone. Our farm would use this grant money to experiment with four different ways of transforming our urban parking lot into a healthy productive farm. Two of the methods involve removing the asphalt completely. The asphalt will be cut into two-foot by one-foot pieces and along with the gravel, will be used to build experimental retaining walls and fences. We believe this is important because if we can discover new uses on the farm for this valuable material we can save a lot of the money that would otherwise be wasted on disposal. After the asphalt is removed we will double dig 40 100-sq-ft beds. The double digging method will ease compaction and add organic matter to the soil, by incorporating six inches of compost, into the soil, at a depth of two feet.

    Furthermore we will compare the advantages and disadvantages of bordered beds by constructing 20 of the 40 beds with borders made out of old tires. The tire board method is something we came across online when we were researching permanent raised beds. This method consists of cutting out the treads of old tires and screwing multiple treads together to form a tire board. The screws hold the tires together because of the wire mesh under the tread. As the screws are driven in, the wire wraps around the threads, locking the screw down tight. The tire boards are then stretched out and held into place with rebar. We want to experiment with this method because we believe it is an excellent alternative to building permanent bordered beds out of wood. The construction of these tires beds can be half the cost of wood beds and the tire beds have the potential of lasting indefinitely. Furthermore by repurposing these tires we will be keeping them out the landfill.

    The other two methods were described in the problems portion of this paper. Those methods consist of leaving the asphalt in place and building beds on top of the asphalts surface. We will build one 100-sq-ft bed using lumber and one 100-sq-ft bed without lumber. These two beds will be built so we can compare the cost, sustainability, labor inputs, and yields of these two beds with the beds built in the soil below the asphalt. By building and comparing these four methods we will be able to determine the most efficient way to restore an asphalt parking lot to a productive growing space.

    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.