By Molly Redfield
Asphalt-strewn streets and blank-faced skyscrapers dominate city landscapes. But in recent years, cities have also become places where anything from rooftop pumpkin patches to herb-crowded windowsills flourish. With the right ingredients—healthy soil, enough sunlight, plenty of water, seeds, and, of course, the space to throw it all together—it seems as if urbanites can now grow a garden anywhere.
But cities are still unique growing environments. Tall buildings can shade out the sun and block or redirect wind. Heavy metals or other pollutants may contaminate the soil. And space in a densely populated city might be difficult to come by. These are some of the concerns, among others, that urban agriculturalists must keep in mind to grow healthy and productive gardens.
Today, Nourishing the Planet highlights five tips that are especially relevant to farmers, gardeners, and other agriculturalists growing gardens in cities around the world.
Soil:Because many cities have a past of rapid industrialization, or are currently industrializing, their soils can contain toxic heavy metal byproducts such as lead or cadmium. Plants uptake these heavy metals through their roots and then incorporate them into their vegetative tissue. When people consume fruits, vegetables, and other products grown in toxic soils they are, often unknowingly, exposed to these contaminants. Children are especially vulnerable to heavy metals and, according to the World Health Organization, a blood lead concentration in children exceeding 10 µg/dL (micrograms of lead per deciliter of blood) is associated with cognitive impairment.
Urban growers have several ways to avoid contaminated soil. One method consists of simply overlaying healthy soils, manure, and loam over contaminated city ground. Instead of completely replacing soils, though, another remedial effort includes mixing organic matter and limestone with city soils. By decreasing the acidity of soils and making lead bind more readily to non-living organic matter, this technique prevents heavy metal uptake in plants. In fact, treating and replacing a depth of only seven inches of city soils can effectively protect the root layer of most common garden plants from heavy metals like lead. Lastly, growing produce out of raised beds or containers with healthy soil is another way for farmers to be certain that their produce is safe.
Sunlight: Ensuring that plants get enough sunlight is one of the biggest concerns urban farmers face. Large cities are sometimes referred to as heat islands because their black asphalt absorbs the sun’s energy instead of reflecting it. Coupled with buildings that shade out sunlight, the minimal light exposure in some city gardens can make it difficult for plants to grow, much less bear fruit. In fact, for popular produce like tomatoes, a minimum of six hours of direct sunlight is suggested. Maintaining a productive garden, therefore, can be particularly difficult in some urban places that only have three hours of sunlight exposure.
An easy way for city growers to increase the amount of light exposure their plants receive is to increase the reflective surfaces near their gardens. Urban residents can paint nearby walls in light colors and place mirrors in locations that will reflect sunlight. Additionally, they can plan to grow smaller gardens in southern-facing patios or windows for maximum sun exposure. An urban agriculturalist may even avoid most of the city’s shading by growing on the rooftops of tall buildings. In the United States, some urban residents even receive tax substitutes and abatements for their rooftop gardens.
Water: Because many urban growers are connected to their city’s municipal supply, finding a source of water for their garden may not be a major concern. But since most of the city’s rainwater enters its sewer system or may be blocked from urban gardens because of other city infrastructure, reusing and saving water can prove beneficial, especially when the month’s utility bill comes in.
Grey water, which is wastewater from household activities like cleaning clothes and taking showers, can be used to water city gardens. Some sources for grey water, however, are more desirable than others. Shower and bath grey water is most preferable for gardens because it doesn’t contain detergents or food particles. For another water-saving technique, city growers can place empty containers at the edges of rooftops to collect runoff rainwater. Additionally, watering at certain times of day is better: watering in the early morning or at dusk increases the likelihood that the water will be used by the plants and will not immediately evaporate into the hot city air.
Plants: Many plants aren’t as well-suited to the particular conditions of urban spaces as others. In some city environments, plants that do well are especially resilient to low light conditions. Because of the limited light exposure and stagnant air, especially in the center of cities where tall buildings and other structures block wind movement, some urban gardeners find that their plants are also particularly vulnerable to mold.
Choosing plants that are appropriate for a city’s environment, such as plants that do not require long hours of direct sunlight, will help urban agriculturalists grow productive edible gardens. Plants that fruit, like peppers, tomatoes, cucumbers, and squash, need several hours of full sunlight, but leafy greens like kale or chard can grow well in the shade, and root vegetables like potatoes and carrots are partially shade-tolerant. Fruiting plants should not be altogether avoided, but being cognizant of their light requirements can help city growers position these plants in the parts of the garden that receive the most sun. In terms of avoiding mold, plants that do not have dense foliage can be less susceptible to mold as these plants promote better air circulation in the garden.
Space: Space is often at a premium in cities. Gardens should, therefore, be planned carefully. Some fruits and vegetables require lots of room to be able to fully mature and produce fruit. For example, smaller fruit trees generally reach full growth at a height of 2.4-3 meters. Therefore, avoiding plants that will not do well in the available space, and maximizing the space that is available, is important when designing an urban garden.
City growers can hang plants to make use of previously unoccupied space. Some produce can be grown upside-down—Topsy-turvy planters, which are available at home and garden stores or which are easily home-made, support the growth of tomatoes, cucumbers, and peppers out of their bottom ends and any right-side-up vegetables out their top ends. Furthermore, if no immediate space for growing is available, city residents can join in community garden efforts and rent out their own plots to grow on. It is important to note, however, that even though city growers want to make the most out of their available space, leaving small footpaths for people to walk through garden plots will help decrease soil compaction and plant damage.
These are just a few tips for city growers to keep in mind for their urban gardens. Why not share your experience with other city gardeners, perhaps even over a locally grown meal!
Do you have any advice or stories to share about your experiences growing in the city? Share them here!
Molly Redfield is a research intern with the Nourishing the Planet project.
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