Urban gardening and farming has risen in the last decade with increasing support from city officials, community leaders, university faculty and students, the farming industry, and governmental organizations. However, increasing green spaces and food production in urban environments is not without its challenges and risks. The two leading obstacles for city residents to safely grow their own food are: (1) availability of space, and (2) soil free from toxic substances. Industry over the last century has dominated urban land, which has led to a rise in soil contaminated with a variety of substances such as heavy metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs).
Challenges and risks associated with urban gardening and farming
• Space availability
• Lack of resources (building materials, soil, water seeds or transplants)
• Adequate sunlight for plant production
• Extreme heat during summer months
• Clean soil free of toxic substances
Recent interests in food production in urban environments have prompted a re-evaluation of soil safety, economic incentives, and the best practices for urban gardening and agriculture. Urban gardening and recreational areas are constrained by space and resources. In locations where there is limited room for raised beds or box plots, vertical gardening becomes an attractive alternative. The Rodale Institute has designed a number of prototypes for vertical gardening called “Growing Towers” and has installed them in the cities of Allentown and Philadelphia, PA.
Growing Towers – Rodale Institute Vertical Gardening Structures
The growing towers are simple structures where the space available for plant production is built vertically in a column or rectangular wall. The structure is held in place using weld-wire, carpenter’s mesh or chain-linked fencing. The height and diameter can vary depending on space availability and plant production needs. A material such as gardening cloth, straw, light-weight fabric or thin cardboard is placed on the inner periphery of the tower to minimize soil loss. The tower is then backfilled with clean compost-amended topsoil. Fruits, vegetables, herbs and flowers can be transplanted into the sides of the tower while transplanting or direct-seeding can occur in the top of the tower after the structure is built and ready for production. Maintenance and other common gardening practices would apply after the column is established and production is underway.
Advantages of Using a Growing Tower
• Creates space vertically for plant production
• Minimizes the risks associated with soil contamination by reducing contact and exposure
• Provides an additional option for urban gardening
• Increases natural beauty in a concrete environment
Tips for Building and Using Growing Towers
The Rodale Institute has been growing fruits, vegetables, herbs and flowers in towers since 2014 and has experienced a number of successes and failures while enhancing growing tower prototypes. Since then, the project managers and collaborators have identified a number of tips that will assist practitioners when building and maintaining growing towers.'
Choosing cost-effective materials: There are several different types of materials that can be used to create the rigid, cylindrical or rectangular structure for growing towers. Each material will vary in cost and availability. Welded-wire for instance, which is used widely by the Rodale Institute, comes in all shapes and sizes. The most cost effective option for welded-wire is one that has a cell size of 2x4 inches. The height of the wire ranges from 3-6 feet and the price adjusts according as the height increases. Other pliable wire such as chicken wire can also be used but this material is less rigid and may buckle under the weight of the soil. Chain-linked fencing is common in city areas and could be adapted into a growing tower with permission from the owner. When building your tower, creativity could be your best tool.
Choosing which plants to grow: The towers presented here offer a unique growing environment for fruits, vegetables, herbs and flowers. After two years of using the towers, the Rodale Institute has noticed that some plants grow better than others. A few of the top performers that had been planted on the side of the tower are kale, Swiss chard, parsley, cilantro, dill, and basil. Several other plants did well such as tomatoes, lettuce and peppers, but required greater attention with watering or training. Most plants had grown very well when planted on the top of the tower. When planting on the sides keep in mind the maximum size of the plant and expect larger plants to hang lower on the tower so be sure not to transplant larger plants on top of smaller plants (e.g., tomatoes planted above dill).
Watering: The vertical growing towers have a greater amount of surface area compared to standard box plots or raised beds and consequently are exposed to more wind. This exposure can cause the towers to dry-out more quickly compared to areas in direct contact with soil. Frequent watering from the top of the tower will aid in maintaining adequate moisture within the tower. Additional irrigation such as perforated PVC tubing inserted into the sides or a large container with holes on the bottom sunken into the soil from the top can be installed to provide water lower in the tower (see image).
Nutrient management: One advantage of the growing tower is that the soil is minimally disturbed between growing seasons; however, due to its design, amending the soil with compost or other soil amendments for nutrient management can be challenging, but there is a solution. Similar to watering, liquid soil amendments such as compost tea and fish emulsion or other liquid organic fertilizers can be applied throughout the tower using the water irrigation system previously mentioned.
Soil compaction: The growing towers can be constructed as tall as six feet with a soil column weighing up to one ton. Even a three-foot tower could contain a cubic yard of soil with a weight of nearly one ton. The vertical design of the tower will cause issues with soil compaction that will make transplanting difficult within a growing season or between seasons. The Rodale Institute is examining solutions for overcoming this obstacle and are finding that amending topsoil with compost, perlite and vermiculite can minimize compaction. Yearly additions of compost-amended soil between growing seasons onto the top of the tower is required. Other options are available but require greater skill when building the tower. For example, creating a column of straw or wood chips down the middle of the tower with 4-6 inches of compost-amended soil on the periphery will greatly reduce weight and compaction.