Greensgrow Farm investigated the feasibility of constructing raised beds in this urban agriculture project. They had four specific objectives:
1. To develop the best design for a raised bed that is situated on an urban brownfield with poor drainage.
2.To determine the best methods of creating good agricultural soil that will support continuous and intensive cropping of a variety of produce.
3. To gauge the overall economic effectiveness of a raised bed as part of an urban farm.
4. To communicate their findings through the publication of a manual that documented design, construction techniques, methods of cultivation, and an analysis of the economic feasibility.
Greensgrow Farm built a 1500 square foot raised bed with a drainage system, drip irrigation, and weed control ground cover. The bed was designed with the drainage system acting as dividers/work paths down the length of the bed, resulting in three beds, each 3 feet wide, for the length of the bed. The drainage system was a critical component of the bed for the urban agriculture environment as the industrial site on which the farm is located is underlain with an impermeable concrete slab.
The bed was filled with large amounts of compost from the City of Philadelphia, large amounts of manure from local stables, and soil fill that was in the bed from the previous year. The materials were mixed and tilled under, analyzed, and amended with sulfur and fertilizer. A drip irrigation system was installed and the beds were covered with black woven weed barrier.
Crops that were grown and marketed to local restaurants included spinach, beets, chard, potatoes, mache, and arugula. The crops produced adequately for the initial season. Due to high pH, some of the potatoes were not as productive as hoped. In December of 2001, they installed a plastic covered hoophouse to extend the growing season in both the fall and spring.
The cost of the raised bed was approximately $2.50/square foot for materials and labor but excluding soil. The hoophouse cost approximately $800. Mat felt that the potential additional returns made the hoophouse addition a worthwhile investment.
Greensgrow Farm also developed two additional designs for constructing a raised bed. The designs for all three beds are included in a manual that has detailed design specifications and drawings, a review of construction techniques, and a discussion of the use of irrigation, mulching, hoophouse coverings, cropping schedules, and an economic feasibility analysis. This manual was written as part of a program to offer professional skills training for urban farmers.