Answer: I am pleased to provide you with information on reclaiming old abandoned asphalt parking lots and the use of soils in urban agriculture.
Farming over asphalt is not new to urban agriculture. The Red Hook Community Farm in Brooklyn, NY is farming on asphalt and the youth who work the farm sell the produce to neighborhood residents at markets in the Reed Hook district. The soil and nutrients for the farm has been constructed through applications of manure from the Brooklyn zoo. You can read a profile of the farm at: http://www.seasonalchef.com/farmredhook.htm
Soil is the most limiting factor in urban agriculture, as buildings, vacant lots, and other infrastructure within your community that can be used for food production may be contaminated. In fact, most urban soils should be assumed to be contaminated by heavy metals and other chemicals unless it has been determined to be safe. Soils used for food production should be held to higher standards of cleanliness than other land uses.
The following is an excerpt from Soil Contamination and Urban Agriculture – A practical guide to soil contamination issues for individuals and groups (see details in the Resources section at the end of this letter):
Ideally, garden soils should have no contaminants, besides the levels that are naturally present in the soil. However, particularly in urban settings, it is inevitable that soil contaminants will exceed natural levels. This raises the question – how much contamination is acceptable? There are standards for acceptable levels of soil contamination which exist at all levels of government. It is important to note that there are different standards– usually pertaining to the industrial, residential, or agricultural use of land. Of these three, agricultural is the most strict, as it is important to have relatively minimal levels of contaminants present in soils that will be used to grow food.
The publication Soil Contamination and Urban Agriculture – A practical guide to soil contamination issues for individuals and groups details methods in evaluating soil contamination, and some options for remediating contaminated soils.
Roof-top gardening can be an excellent option if soils are contaminated. Rooftop gardens are a unique way to use unused and sterile spaces for food production. There are many different types of rooftop garden systems that can include growing crops in containers, in raised beds, or even greenhouses. Rooftop gardens not only provide food, but also help cool buildings and can improve air quality.
Raised bed gardening is another method for dealing with contaminated soils in urban agriculture projects, and can be used over contaminated soils or asphalt. Raised beds can be constructed with non-treated wood or bricks and filled with soil to a depth greater than the rooting zone of the plants being grown. Wood chips can be used in the walk ways to prevent contaminated dust from soil from being kicked up and contaminating the food plots. An example of a raised bed is detailed in the Food Project’s raised bed manual, as referenced below.
If soil is a limiting factor, I would suggest starting a community composting project. This would help to develop a source of organic matter that the whole community could participate in, while reducing the waste stream in your community. The organization Community Compost has a lot of information on this topic and would be a good start. Note: they are a British organization, but many of the issues/considerations still apply.
Consider not only plant crops but animals as well. Vegetables are a very small proportion of most diets. Having chickens, other foul, and maybe some other forms of protein should be considered when growing more local foods, and the animals’ manure can be used to build soil fertility in the gardens.
There is a new movement in urban areas called SPIN farming—or Small Plot Intensive farming. This type of market gardening grows on small plots of land either private or community-based, focusing on succession planting and intensive cropping systems. Thy have several guides, and they are not free of charge unfortunately, but they are nominally priced. Below is a link to the official SPIN web site:
I have listed several resources on urban soils, contamination, and remediation below for your review.
Craul, Phillip J. 1999. Urban Soils: Applications and Practices. Wiley Publishing. See www.amazon.com.
The soil which is found in large cities offer distinctive challenges to the landscape architect or horticulturist responsible for maintaining these urban plantings. Often compacted, contaminated, or otherwise unsuitable for use in major landscape projects, these soils require practical methods which can insure a successful outcome of a landscape project. This applications-oriented, introductory reference addresses numerous topics in the field of urban soil science.
Flynn, Kathleen. 1999. An Overview of Public Health and Urban Agriculture: Water, Soil and Crop Contamination & Emerging Urban Zoonoses (Includes Institutional Directory and Annotated Bibliography). International Development Research Centre (IDRC) Intern.
This report provides an initial exploration into the potential health hazards associated with various practices in urban agriculture and highlights research which endeavours to protect producers and consumers from these hazards.
Food Project. The Food Project’s Urban Education and Outreach Raised Bed Building Manual.
Includes pictures of many of the steps and descriptions and prices for materials.
Guide to Setting Up Your Own Edible Rooftop Garden. Rooftop Garden Project, Montreal, QC.
This publication contains over 80 pages and is available to download from the website. If you are unable to download the publication, it can be obtained by contacting the organization Alternatives by telephone at (514) 982-6606 x2230.
Heinegg, Alexandra, Patricia Maragos, Edmund Mason, Jane Rabinowicz, Gloria Straccini, and Heather Walsh. 2002. Brownfield Remediation: Solutions for Urban Agriculture. Submitted in partial fulfillment of the requirements for ENVR 401 Environmental Research. McGill School of Environment, McGill University.
Due to the history of industrial and urban pollution, many sites that are potentially desirable for urban agriculture are simply too polluted to safely grow food. These contaminated sites are known as brownfields. As a solution to this problem, there are a number of soil remediation techniques available with varying cost, timeframe, accessibility and effectiveness. The goal of this project was to prepare a guide for community organizations addressing the topic of brownfield remediation as a solution for urban agriculture.
Heinegg, Alexandra, Patricia Maragos, Edmund Mason, Jane Rabinowicz, Gloria Straccini, and Heather Walsh. 2002. Soil Contamination and Urban Agriculture - A practical guide to soil contamination issues for individuals and groups. McGill School of Environment, McGill University.
This guide is written as a primer on soil contamination, as it relates to gardening in an urban setting. It seeks to provide individual gardeners or community groups with the necessary background information to address this issue. There are several important aspects of soil contamination which are addressed in this guide, including the dangers of gardening in contaminated soil, the potential sources of contamination, ways to evaluate the level of contamination present in the soil, and your options for addressing the problem. At the end of this document there are several appendices with information pertaining to the topics discussed here. Most of these are Montreal- and Canada–specific, but should provide some good starting points for similar resources in other cities and countries.
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