Puzzle pieces laying over a city building.
Updated: March 17, 2021
By Neith Little

Chapter 1: Urban production systems

In agricultural contexts, the word production is used as short-hand to refer to all the activities involved in physically growing, raising, or making the products (vegetables, flowers, meat, eggs, hot sauce, an agritourism experience, etc.) that will eventually be sold. Important non-production agricultural activities include financial planning, marketing, complying with legal responsibilities, and managing human resources (see the other chapters of this guidebook)

This chapter will describe the types of production systems used in urban agriculture and introduce important topics that an urban farmer will need to consider to successfully produce a product for sale and manage production risks.

As described in the introduction, urban agriculture is diverse and includes a wide variety of production systems and business models. This chapter will focus on the scale and challenges most relevant to urban farmers and urban agriculture entrepreneurs who sell what they produce (whether for-profit or not-for-profit).

Production systems

Figure 1: Outdoor urban agriculture can be done in raised beds or containers, in-ground in native or imported soil, and in high tunnels or hoop houses. Picture taken at Whitelock Community Farm, Baltimore, MD by Neith Little, UMD Extension.
Figure 1: Outdoor urban agriculture can be done in raised beds or containers, in-ground in native or imported soil, and in high tunnels or hoop houses. Picture taken at Whitelock Community Farm, Baltimore, MD by Neith Little, UMD Extension.
 

Although any one individual urban farm might use multiple methods to grow crops and raise livestock, urban agriculture production systems can be broadly categorized as

  • Ground-based outdoor urban farming
  • Hydroponic or aquaponic indoor production
  • Rooftop farming
  • Landscaping and nursery businesses
  • Urban livestock production
  • Mushroom production (fungiculture)

A recent survey of urban farmers in Maryland found that the majority grew vegetables, fruits, and cut flowers in land-based production systems using raised-beds, in-ground growing, and high tunnels (Little et al. 2018).

Across all production systems, the types of crops and livestock that fit most easily into an urban agriculture business are ones that are physically small, thrive in small spaces and challenging growing conditions, and have fast life cycles. The last point is important to maximize the amount of income or food produced per square foot. Slower growing crops (like fruit trees) or livestock (like oysters) can be important parts of an urban agriculture system, but their slow life cycles mean that they consume more space and time per unit of food produced than faster-growing crops and livestock.

Ground-based outdoor urban farming:

Figure 2: Lettuce being grown in a high tunnel at Strength to Love 2, in Baltimore, MD. Photo by Neith Little, UMD Extension.
Figure 2: Lettuce being grown in a high tunnel at Strength to Love 2, in Baltimore, MD. Photo by Neith Little, UMD Extension.

Ground-based outdoor urban agriculture is particularly common in cities with large amounts of vacant land, such as Baltimore and Detroit. Production practices include growing in-ground in the native soil, on the ground (or even on pavement!) in imported soil or growing media, in raised beds or containers, and in high tunnels or hoop houses which are used to extend the growing season and protect the crops from extreme rain events (Figure 1 and 2). Most ground-based urban agriculture is used for diversified vegetable production, but some urban farms grow perennial fruits, and a subset of urban farms specialize in cut flower production.

 

 

 

A note about specialty ethnic vegetables: Urban growers may be particularly interested in growing specialty vegetable varieties featured in the cuisines of the ethnicities and cultures of the community around the urban farm. Learn more about specialty and ethnic crops here https://go.umd.edu/specialtyveg and in the references at the end of this chapter (Tubene and Myers 2008; Afantchao 2010; Mangan 2002).

Hydroponic or aquaponic urban farms:

Figure 3: Basil grown hydroponically in a plug floated in a foam mat on top of a tank of water, at Envista Farms at Southern Friendship Missionary Baptist Church, in Temple Hills, MD. Photo by Neith Little, UMD Extension.
Figure 3: Basil grown hydroponically in a plug floated in a foam mat on top of a tank of water, at Envista Farms at Southern Friendship Missionary Baptist Church, in Temple Hills, MD. Photo by Neith Little, UMD Extension.
 

Hydroponics means growing plants using water as the primary method of delivering nutrients. Hydroponic plants may be rooted in a small amount of non-soil growth medium, like a plug (Figure 3) or mat, or they may grow directly in the water.

Aquaculture is the practice of raising seafood in a defined space, for example raising fish in tanks or ponds or raising shellfish in cages in a bay.  

Aquaponics is a growing practice that combines hydroponics and aquaculture, where seafood is raised in tanks and filtered waste nutrients from the seafood are used to fertilize the plants.

Hydroponic or aquaponic urban farming is done in a wide variety of ways which differ in how much natural versus artificial light is used, and how the plants are suspended in the water.

Figure 4: Greens and fish grown aquaponically in a high tunnel using natural light, at University of the District of Columbia Food Hub, in Washington, DC. Photo by Neith Little, UMD Extension.
Figure 4: Greens and fish grown aquaponically in a high tunnel using natural light, at University of the District of Columbia Food Hub, in Washington, DC. Photo by Neith Little, UMD Extension.
 

Plants may be grown in high tunnels using natural light (Figure 4), in greenhouses using both natural and supplemental artificial light (Figure 5), or indoors in buildings or shipping containers using solely artificial light (Figure 6).

Common crops are microgreens, herbs, and leafy greens. A helpful analysis of the potential and limitations of artificial light is provided by a recent article by Pattison and colleagues (2018).

Greenhouse and indoor production is considered Controlled Environment Agriculture. Zero-acreage farming or vertical farming includes both production inside buildings and rooftop farming.

Figure 5: Collard greens grown hydroponically using both natural and supplemental artificial light at Envista Farms at Southern Friendship Missionary Baptist Church, in Temple Hills, MD. Photo by Neith Little, UMD Extension.
Figure 5: Collard greens grown hydroponically using both natural and supplemental artificial light at Envista Farms at Southern Friendship Missionary Baptist Church, in Temple Hills, MD. Photo by Neith Little, UMD Extension.
 
Figure 6: Basil grown hydroponically in a modified shipping container at Urban Pastoral, in Baltimore, MD. Photo by Neith Little, UMD Extension.
Figure 6: Basil grown hydroponically in a modified shipping container at Urban Pastoral, in Baltimore, MD. Photo by Neith Little, UMD Extension.
 

 

Rooftop:

Rooftop farms are most common in cities with high land and real estate costs, like Washington, DC and New York City.

Some rooftop farmers build growing containers from scratch, but this may be limited to the edges of roofs where the existing architecture is strongest. Other rooftop farmers retrofit existing green roofs to produce crops for sale. Common crops are strawberries (Figure 7), vegetables (Figure 8), and cut flowers (Figure 9).

Figure 7: Strawberries grown in a container on a rooftop at University of District of Columbia, Washington, DC. Photo by Neith Little, UMD Extension.
Figure 7: Strawberries grown in a container on a rooftop at University of District of Columbia, Washington, DC. Photo by Neith Little, UMD Extension.
 
Figure 8: Okra growing on a retro-fitted green roof at Up Top Acres, in Washington, DC (note the Washington Monument in the background). Photo by Neith Little, UMD Extension.
Figure 8: Okra growing on a retro-fitted green roof at Up Top Acres, in Washington, DC (note the Washington Monument in the background). Photo by Neith Little, UMD Extension.
 
Figure 9: Flowers growing on a retro-fitted green roof at Up Top Acres in Washington, DC. Photo by Neith Little, UMD Extension.
Figure 9: Flowers growing on a retro-fitted green roof at Up Top Acres in Washington, DC. Photo by Neith Little, UMD Extension.
 

 

 

Landscaping and nurseries:

Figure 10: Plant nurseries and landscaping businesses located in cities are part of the urban agriculture. Photo by Edwin Remsberg, © University of Maryland—AGNR Image Library.
Figure 3: Basil grown hydroponically in a plug floated in a foam mat on top of a tank of water, at Envista Farms at Southern Friendship Missionary Baptist Church, in Temple Hills, MD. Photo by Neith Little, UMD Extension.
 

Landscaping companies, arborists, and plant nurseries located in cities are also considered a kind of urban agriculture (Figure 10). These types of businesses sometimes refer to themselves as part of “the green industry.”

In addition to traditional landscaping companies, edible landscaping is a growing trend (Figure 11). Edible landscaping companies can be hired to build or maintain vegetable gardens and fruit plantings for private homeowners and for corporate or municipal buildings, the same way landscapers have traditionally planted and maintained ornamental plantings.

Figure 11: Converting lawns to vegetable gardens is a popular trend, which edible landscaping companies are turning into a business model. Photo by Josh Rosenstein, Edible Eden, Baltimore, MD.
Figure 11: Converting lawns to vegetable gardens is a popular trend, which edible landscaping companies are turning into a business model. Photo by Josh Rosenstein, Edible Eden, Baltimore, MD

Urban livestock:

Figure 12: Urban agriculture can successfully integrate small livestock, such as rabbits or miniature goats. Photo by Edwin Remsberg, © University of Maryland—AGNR Image Library
Figure 12: Urban agriculture can successfully integrate small livestock, such as rabbits or miniature goats. Photo by Edwin Remsberg, © University of Maryland—AGNR Image Library

The types of livestock raised in urban areas are constrained by both space and local regulations. Some municipalities allow the keeping of some kinds of poultry (chickens, turkeys, quail, etc.), miniature goats, bees, or rabbits. More unusual, innovative “livestock” like fish, shellfish, earthworms (red wigglers, specifically), mealworms, snails, black soldier flies, and crickets are also raised by some urban farms. Be sure to check with your local zoning office and also find out what permits are required to keep animals in your area. For example, in Baltimore City, miniature goats are allowed with a permit, but other breeds of goats and sheep are not allowed. Please also note that local municipalities may regulate slaughter within city limits.

Poultry, goats, rabbits, bees, and composting earthworms are often integrated into outdoor urban production systems. For example, chickens might be allowed to forage for pests and vegetable scraps in a vegetable bed after harvest, and their droppings might become part of the nutrient input into the soil, whether by “direct deposition” or after composting the litter from the hen house. Aquatic livestock are sometimes grown alone (aquaculture) or integrated into hydroponic crop production (aquaponics).

Learn more about raising the kinds of livestock suited to urban agriculture: https://go.umd.edu/morelivestock

Integrating livestock and crop production systems has a lot of potential value for environmental and economic sustainability. However, when integrating livestock with crop systems food safety planning and nutrient management planning become more important.

Mushroom production (fungiculture):

Figure 13: Mushrooms can be cultivated outdoors or indoors. The photo on the left shows mushrooms grown outdoors at Real Food Farm, Baltimore, MD and on the right is a display of mushrooms grown indoors by Sharondale Farms. Photos taken by Neith Little, UMD Extension
Figure 13: Mushrooms can be cultivated outdoors or indoors. The photo on the left shows mushrooms grown outdoors at Real Food Farm, Baltimore, MD and on the right is a display of mushrooms grown indoors by Sharondale Farms. Photos taken by Neith Little, UMD Extension
 

Edible mushrooms can be cultivated outdoors on inoculated logs, or indoors on a substrate such as sawdust, grain, or compost. Outdoor production is popular with hobbyists and farmers who have small woodlots. Indoor production is more common among mushroom producers who specialize in growing mushrooms for sale and is particularly well-suited for urban agriculture that attempts to produce food indoors in underutilized buildings. For all mushroom production methods, success depends on careful attention to sterile procedures and inoculation methods.

Learn more about fungiculture: https://go.umd.edu/moremushroom


           

Production topics to learn more about

Across production systems, there are several important urban production topics a grower will need to learn about and consider in their risk management planning:

  • Urban soils and growing media
  • Soil contamination assessment and risk management
  • Nutrient management
  • Crop rotations and crop planning
  • Water management
  • Pest management: weeds, diseases, insects, and more!
  • Season extension
  • Harvest, post-harvest storage, and food safety

There’s a lot to learn. This section will give you a brief introduction to key concepts within each topic, to help you identify what you need to learn more about next.

Urban soils and growing media:

One of the common denominators I’ve observed among farmers who grow plants is that they will talk for hours about what they grow their plants in. Rural farmers? They complain about how many rocks they have in their soil and brag about their organic matter content. Ground-based urban farmers? They swap tips and tricks for building up healthy soil from construction rubble, reducing compaction, and avoiding contamination. Hydroponic urban farmers? They argue passionately about whether coconut coir plugs are better than peat moss plugs, or whether it’s best to put the roots directly in the water (nutrient film technique) or in air with misted water and nutrients (aeroponics).

Whatever you grow your crops in, how well you understand it and manage it will have a huge impact on how well your plants grow.

What is soil? What is a growing medium?

Soil is the result of a mind-bogglingly long process wherein the rocks of the earth’s crust are gradually broken down into very small particles by the environment and living organisms. Soil is made of tiny particles of rock (sand, silt, and clay are size classes of tiny rock particles), dead biological material (organic matter), and living organisms (from “macroinvertebrates” like worms down to microbes, fungi, and viruses).

In some places, growers are blessed with soil that is well suited to growing plants. In other cases, the native soil requires amendment with other materials to improve its ability to support life. Many outdoor urban growers have added so much organic matter in the form of compost or wood chips, that the "soil" they grow in might more accurately be called a growing medium. In some cases, growers start from scratch by importing soil from elsewhere or using a "soilless growing medium:" a mix of materials like peat, coconut coir, vermiculite, perlite, wood chips, course sand, or compost. Hydroponic or rooftop growers might use specialized growing media such as rockwool or clay pebbles (hydroton).

Historically, rural farmers grew in soil and plant nurseries grew in pots of soilless growing media. But, as in many other areas, urban farmers are trying new things and blurring the lines between what used to be distinct categories. Applied researchers are working hard to expand our scientific understanding of the growing media urban farmers use, and what best practices we can recommend.

If you are growing outdoors in soil, you’ll probably need to learn about soil science: what size your soil particles are and how they affect how well your soil holds water and air, how your soil’s chemical properties (pH, fertility, cation exchange capacity, organic matter) affect your crops, which organisms that live in soil are beneficial and which cause problems, and how you can work to improve some of these things. Various soil tests can tell you a lot about these soil properties.

If you are growing primarily in something other than soil, whether outdoors, in a high tunnel, or using hydroponics, you may be able to learn from the experience and research of the plant nursery industry. You’ll still need to understand your growing medium’s chemical properties, but you’ll need to use tests designed for growing media, not soil. You’ll also need to pay particular attention to your growing medium’s salinity (electro conductivity) and the quality of the water you use. And when deciding what growing medium to use remember that, as in many parts of life, a  mix is usually better than too much of one thing. For more information on growth media, go to https://go.umd.edu/growingmedia

 

Soil contamination assessment and risk management:

This topic brings up a lot of fear and strong emotions, which makes it extra important to make decisions using good information about how soil contamination works and about your specific situation.


What are soil contaminants?

Most contaminants of soil that might pose a risk to human health fall into one of two categories: the so-called “heavy metals” (lead, arsenic, cadmium, chromium, copper, mercury, selenium, zinc) and complex organic compounds (solvents, pesticides, creosote, petroleum). Heavy metals are naturally occurring elements and are relatively easy to test for—many soil labs offer a test that will measure all of these metals for $40 to $100. Labs that offer tests for organic compounds are more rare, and the tests are more expensive and are specific to different types of organic contaminants.


Organic compounds eventually break down over time into smaller molecules, but metals are elements—they’re as small as they’re going to get in a human time-scale—so once they’re in a soil you’re pretty much stuck with them. On the other hand, some organic compounds can be taken up by plants’ roots into the parts of plants that people and animals eat. But at normal soil pH most metal contaminants bind so tightly to the soil that plant roots cannot take them up. This means that if your soil has heavy metals in it, the most important risk management tactic is to keep the soil itself out of people’s bodies: avoid growing crops who’s edible portions contact the soil, and minimize dust that could be inhaled.


Knowledge is power

The good news is that soil contamination is very site-specific, and many sites are relatively fine. Surveys of lead in soils across Baltimore, MD have found that only a small percentage of sites surveyed have lead levels higher than the EPA’s threshold of 400 ppm (Mielke et al. 1983; Yesilonis et al. 2008). This is likely because after the fire of 1904, Baltimore required most buildings to be made of brick, which is less likely to have exterior lead paint (interior lead paint is another story). Thus atmospheric deposition from leaded gasoline was probably the largest source of lead outdoors. Johns Hopkins University’s Center for a Liveable Future is in the middle of an ambitious Safe Urban Harvests study in Baltimore, so keep an eye out for updated data soon.


So does this mean you don’t need to worry? No, this means that it’s worth spending the money to test your soil for heavy metals so that you will know what you are dealing with. If you are early in the process of finding a place to grow, getting the soil tested for heavy metals will help you find a site to grow that has less metal contaminants. And if you already have a growing site, testing will give you information you need to decide whether you need to take steps to reduce your risk.

 

Even if you are farming in a rural area, depending on your site history it might be worth testing for heavy metals. Many old fruit orchards have high lead and arsenic contamination, because from 1890 to 1947 lead arsenate was commonly used as a pesticide in fruit orchards across the US (Schooley et al. 2008).


How much is too much?

This is the tough question, and unfortunately the answer is not cut and dry.


Legally, there are no federal standards for acceptable levels of contaminants in agricultural soil. The EPA sets thresholds for contaminants in brownfield sites that must be cleaned up before being returned to public use (EPA 2001, EPA 2002), but they will be the first to admit that those thresholds were never intended to be used for agricultural decision-making (EPA 2011).


States and local municipalities sometimes set their own standards for soil contaminations. The Maryland Department of the Environment (MDE 2008) and the New York State Department of Environmental Conservation have set local Soil Cleanup standards (NYSDEC & NYSDH 2006). Baltimore City has a draft Soil Safety Policy for Food Production which requires growers who want to make food production the official zoned use of their site to first test for soil contamination and have a plan to reduce risks based on the results of those tests (Baltimore Office of Sustainability 2014).


When weighing the risk posed by soil contaminants at your specific site, consider federal and local standards, expected local background levels in uncontaminated soils, and whether children will be gardening at your site.

Risk mitigation

At the pH that is best for crop growth, metals bind tightly to soil particles (Brennan and Lindsay 1996; Elliot et al. 1986) and are unlikely to be taken up into the edible part of a crop (Brown et al. 2016; Chaney et al. 1984). Rice is an important exception to this rule, because it is prone to taking up arsenic into the rice grains (Wang et al. 2003).


This means that on sites with metal contaminants, the most important mitigation goal is to keep the soil out of people’s bodies. Tactics that minimize how much farmers and gardeners are exposed to contaminated soil will also reduce the risk to customers. Relatively easy risk management strategies are to

  • avoid growing crops where the edible portion contacts the soil (root crops, lettuce),
  • keep bare soil covered with mulch, cover crops, or grass (under crops, in walkways, adjacent to growing areas),
  • minimize how much you disturb the soil (low-till or no-till),
  • avoid tracking soil into vehicles and living areas (wear gloves, use designated clothes and shoes for farming/gardening, wash dirty boots before leaving the growing area),
  • in high risk situations (very high contaminant levels, children gardening, growing root crops or lettuce) grow in raised beds filled with a soil or growing medium that is known to be uncontaminated.

 

What about phytoremediation?


Over recent decades, many growers and researchers have been excited by the prospect of using plants, particularly sunflowers, to selectively take up contaminants from the soil and remove them (phytoextraction).


The bad news is that lead is usually so tightly bound to the soil that trying to extract it with plants would take centuries, and you'd still need to figure out what to do with all that contaminated plant matter.


The good news is that because lead binds so tightly to the soil, it is much more practical to phytostabilize, by adding organic matter and other materials to make the lead even less bioavailable and more dilute in the soil. For a good summary of the research, see Blaustein (2017).

 

Soil maps:

If you grow outdoors, a map may already be available showing your soil’s texture and other characteristics. This information can be a valuable resource to help you learn about and better manage your soil. The United States Department of Agriculture Natural Resources Conservation Service (USDA-NRCS) offers a searchable online map of soils called the Web Soil Survey: https://go.umd.edu/websoilsurvey

Unfortunately, in urban areas it is common for construction to have changed the soil at a site since the mapping was done. This means that the Web Soil Survey is a good place to start, but you will need to determine whether the information it provides is still accurate for your site. Additionally, the Web Soil Survey was not designed to be accurate at very small scales. Fortunately, the USDA-NRCS is aware of this issue and has been working to conduct revised soil surveying specific to urban areas: https://go.umd.edu/NRCSurbansoils

 

Nutrient management:

Figure14: Plants take nutrients up through their roots and use them to build their bodies, including the parts we and animals eat.
Figure 14: Plants take nutrients up through their roots and use them to build their bodies, including the parts we and animals eat.

Plants need nutrients, like nitrogen (N), phosphorus (P), and potassium (K), to build their bodies. Different soil amendments add different amounts and forms of nutrients to the soil.

Soil fertility amendments could be fertilizers, composts, manures, or other materials that contain plant nutrients. Fertility amendments for sale should come with a label that reports their nitrogen (N), phosphorus (P), and potassium (K) concentration, by weight. These three nutrients are needed by crops in large amounts and are sometimes referred to as NPK.

Usually the label will report the NPK concentration as three numbers. The first number is the nitrogen concentration, the second is the phosphorus concentration, and the third is the potassium concentration. Nutrients in commercial fertilizers tend to be concentrated and quickly available. Nutrients in compost and manures tend to be less concentrated, and in bigger molecules that become available over a longer period of time. Compost and manure also supply other nutrients and organic matter.

More accurately, in the US most fertilizer labels and recommendations are calculated as available nitrogen (N), phosphate(PO), and potash (KO) instead of elemental nitrogen (N), phosphorus (P), and potassium (K). But for pronounceability’s sake the N-PO-KO ratio is often referred to as the N-P-K ratio. Because we pretty much all use the same system, you should not have to convert between available phosphate (PO) and elemental phosphorus (P), so you don’t really need to worry about it. N-PO-KO and N-P-K should mean the same thing in most situations where you will encounter them. Unless you go to Europe, or into a research lab. Then all bets are off.

A fertility test can tell you what nutrients are already in your soil, and what nutrients you need more of. Soil and growing media use different test methods to measure fertility. Different tests should be used to measure the fertility of soils and growing media.

In Maryland, if you farm and sell at least $2,500 worth of crops per year, you are legally required to have an official nutrient management plan. To learn more about this rule, and how to get a nutrient management plan, go to http://extension.umd.edu/anmp

Learning more about how nutrients cycle through the soil, atmosphere, plants, and animals can help you improve your crops’ growth and use purchased inputs most efficiently. To start with, know that nitrogen is particularly mobile in the soil, water and air, and that it exists in many different forms. This means that in places that get a lot of rain during the growing season (like the eastern United States), measuring soil nitrogen at any one moment will not tell you much about how much nitrogen will be available a month from then. So many soil tests will not report nitrogen measurements and will instead recommend adding nitrogen based on book values for how much nitrogen specific crops need.

Nitrogen is also often the nutrient that limits plant growth and is particularly expensive to purchase using organic amendments. So if growing using organic methods is important to you, you will need to learn about cover crops. Leguminous cover crops (beans and peas) fix nitrogen from the air and put it into the soil. Other cover crops can “catch” nitrogen left over in the soil at the end of the growing season, and help hold it until the next spring. To learn more about cover crops, a good book to start with is Managing Cover Crops Profitably by Andy Clark. A free digital version is available online from Sustainable Agriculture Research and Education: https://www.sare.org

Nutrient management can be an intimidating topic, because it involves chemistry and math. But if you keep learning more every year, you’ll find that understanding your crops’ nutrient needs, what your soil provides, and what you add to it will help you grow better crops and spend your money more wisely.

Crop rotations and crop planning:

What is crop rotation and why would someone do it?

Figure 15: Start thinking about crop rotation by imagining you have three beds (A, B, and C), and you plant the same crop in each bed every year.
Figure 15: Start thinking about crop rotation by imagining you have three beds (A, B, and C), and you plant the same crop in each bed every year.

Imagine a simplified urban farm with three beds: A, B, and C. In bed A, you plant tomatoes, in bed B you plant collard greens, and in bed C you plant peas (Figure 15).

Next year, out of habit, you do the same thing. And the same thing the year after that.

If you keep doing this year after year, eventually you run the risk of having diseases specific to each crop build up in the soil. But because each of these crops come from different plant families, many diseases that infect tomatoes do not infect collard greens, and vice versa. So a good strategy to prevent disease is to rotate your crops from bed to bed every year (Figure 16). This means that tomato disease agents left in the soil after year 1 will have no suitable host in years 2 and 3, and will be more likely to die off before tomatoes are planted again in year 4. This is crop rotation.

Figure 16: An example of a simple crop rotation design. Every year you shift which crop you plant in which bed. This helps break up disease and pest life-cycles, and helps replenish the nutrients in the soil.
Figure 16: An example of a simple crop rotation design. Every year you shift which crop you plant in which bed. This helps break up disease and pest life-cycles, and helps replenish the nutrients in the soil.

By rotating your crops like this, you not only reduce the risk of disease, you also take advantage of the fact that your peas are a nitrogen-fixing legume. Every year they pull some nitrogen out of the air and leave it in the soil. If you grow a crop that needs a lot of nitrogen, like collard greens, in a bed that had peas the previous year, the collard greens will benefit from the nitrogen that the peas left in the soil.

An advanced crop rotation plan will balance many factors like diseases and nutrient needs. To learn more, a good book to start with is Crop Rotation on Organic Farms, by Charles L. Mohler and Sue Ellen Johnson. A free digital version is available online from Sustainable Agriculture Research and Education: https://www.sare.org

Less information is available about how to apply the principles of crop rotation to indoor production, but understanding what pests and diseases affect which families of crops is still valuable. The next topic, crop planning, is crucial for both outdoor and indoor farms.

 

Community Supported Agriculture (CSA):

A type of direct-marketing where customers pay the farmer for a weekly box of produce throughout the growing season. Most CSA "shares" are paid up-front in the winter or early spring, but some farmers accept multiple smaller payments. Some urban growers use other terms like "produce subscription" or "Netflix for vegetables" to market a CSA share to customers who are unfamiliar with the concept.

What is crop planning and why would someone do it?

In the Marketing chapter, you’ll hear from Ginger and Kim that they encourage farmers to plan where you will sell your crops before you even plant them.

So let’s imagine you plan to sell vegetables through a Community Supported Agriculture (CSA) weekly farm share. You want to deliver to thirty customers a box of at least three different kinds of fresh, delicious vegetables every Friday, from June through September. You can then plan backwards from this goal to figure out what you need to plant when, and how much of it! This is crop planning.

Seed labels and catalogs can be a helpful resource in this process. Some things to consider include

  • the average frost dates in the spring and fall for your location (if growing outdoors),
  • what crops are best suited to the cool parts of the season (lettuces, brassicas, and most herbs, for example) and what crops need the heat of summer to thrive (tomatoes, peppers, okra, and sweet potatoes, for example),
  • which crops can be direct-seeded and which will need to be started earlier as transplants,
  • how much space different crops take up and roughly how much produce you can expect each plant or square foot to yield,
  • roughly how much time different crops need to produce their edible portion (“days to maturity” on a seed packet) and whether it will be possible to “succession plant” multiple crops in one spot at different times in the growing season.

Succession planting has two meanings:

  1. Growing multiple crops in the same space, but separated by time. For example, you could plant spinach early in the spring, pick spinach leaves throughout the spring, pull up or till under the spinach in late spring, and plant tomato transplants in the spinach’s place. The spinach cannot tolerate the heat of summer and will bolt and the tomatoes need the heat of the summer and cannot be planted outdoors before the last risk of frost, so you grow them in the same place in succession to maximize how much food you can produce per square foot.
     
  2. Planting the same crop in different places, but on multiple planting dates, to stagger their maturity and harvest dates. For example, you could plant one row of cilantro every week in April, so that you would be able to cut big beautiful bunches of cilantro from each row in succession for your weekly farmers market in May.

Crop planning is important not just for CSA farmers, but also for other market outlets such as farmers' markets or contract growing. For example, farms that are associated with schools need to carefully plan how to deliver food during the school year, which is not the traditional growing season in the US! Tufts University offers a very helpful crop planning lesson module at https://nesfp.org/resources/crop-planning-module.

For crop planning in Maryland's climate, this color-coded planting calendar is a fantastic resource: https://go.umd.edu/plantingcalendar.

Urban farms that use high tunnels to extend the growing season and farms that use hydroponic methods to grow indoors will also find crop planning crucial.

In high tunnels or hoop houses, crop planning will help you efficiently use your limited sheltered space and work with the seasons. In particular, if you are trying to grow year-round, note that in northern and Mid-Atlantic climates even in a high tunnel plant growth slows dramatically in the winter. Farmers I’ve known who have successfully used their high tunnels through the winter have been careful to get their winter crops planted at just the right time in the fall so that the crop will have time to grow to the early edible stage before the cold sets in, and the high tunnel will then almost act as a stasis field through the coldest part of the winter—keeping the crops alive and fresh but not growing much more, so they can be harvested in the winter when few other sources of local produce are available. Elliot Coleman’s books Four Season Harvest and The Winter Harvest Handbook are the foundational texts on season extension in cold climates. University of Delaware Extension has researched recommended planting dates for high tunnels in our climate region: https://go.umd.edu/hightunnelplanting

In hydroponic and aquaponic urban farming, efficiently producing the most food per unit of space and time is crucial for covering the start-up, maintenance, and utility costs of a hydroponic system. In this case, the succession planting part of crop planning is particularly important. Successful hydroponic farmers spend time figuring out how long it will take their system to produce different kinds of crops, and how to stagger planting dates to enable them to harvest continuously.

For example, as an aquaponic urban farmer you might start a small amount of several different kinds of greens and herbs as plugs every week, so you can plant a few flats of new plugs in your float tank every couple of weeks and harvest a few flats every week for a farmers market (succession planting type 2 above).

Alternatively, a hydroponic or aquaponic grower selling a large amount of lettuce to a cafeteria every month might plant their entire growing space at one time on a date calculated so that the lettuce will be mature in time for the contracted delivery date. However, such a grower would need a large amount of space for plug production so they could be ready to plant again immediately after harvest (succession planting type 1 above).

In summary, crop rotation is an important strategy to manage production risks such as pest and disease pressure and nutrient deficiency. Crop planning is an important strategy to manage market risks, enabling you to plan what and when you grow with your end market in mind, and enabling you to take advantage of the opportunities offered by the lower supply of fresh, local vegetables in the early spring, late fall, and winter.

 

Season extension:

Growers producing food for the local market use a variety of methods to extend the growing season beyond what is traditionally possible in the local climate.

Season extension methods can be as low-tech as starting transplants indoors and laying inexpensive row cover cloth over small metal hoops to create “low tunnels.”

High tunnels or hoop houses are mid-range options. As opposed to greenhouses, high tunnels are usually made of less expensive materials with flexible plastic coverings, in-ground or raised beds (as opposed to bench-top production), and passive heating and cooling such as row covers and roll-up sides. Some local zoning boards consider high tunnels as temporary structures (check your local rules first!). The relatively low construction and maintenance costs and the potential (with significant work!) to move a high tunnel to a new site if necessary have made high tunnels popular with urban farmers.

Penn State Extension has particularly good resources on high tunnel construction and management. And the USDA-NRCS has offered incentive grants to help farmers build high tunnels to extend the growing season.

 

As a side-note, low tunnels are also a valuable pest-exclusion technique. They can be used to exclude pests that have a known, brief population surge every year or to give young crops a head start to outgrow pest pressure.

 

Greenhouses with permanent plastic or glass walls, supplemental lighting, and heating systems, are much more expensive and are mostly used at a small scale for transplant production and at a large scale by plant nurseries to produce potted plants for sale to public customers or to landscapers and garden centers.

Indoor production could also be considered a form of season extension. There are also hybrids of the various methods, with some aquaponic urban farmers setting up their systems in high tunnels and ground-based urban farmers using double-envelope systems of low-tunnels within high tunnels to maximize the temperature differential between what the crop experiences and the outside temperature.

Pest management: weeds, diseases, insects, and more!

Pests can quickly eat up an urban farmers’ yields and profits—quite literally!

Figure 17: The holes in this eggplant are an example of the kind of cosmetic damage that insect feeding can cause. Photo by Neith Little.
Figure 17: The holes in this eggplant are an example of the kind of cosmetic damage that insect feeding can cause. Photo by Neith Little.
 

How to prevent and control pests is a huge topic; much bigger than can be satisfactorily covered here. This section will introduce the “big three” types of pests, basic elements of a pest management strategy, brief thoughts on how these pests and strategies apply to urban farming, and links to references where you can learn more.

The big three: Some people think of pests as specifically animals: insects, other invertebrates, and vertebrate critters like rodents, deer, and birds. Other times people will include weeds and diseases within the definition of “pests.” All these kinds of pests can reduce crop yield, harm livestock, and cause cosmetic damage that makes fruit and vegetables undesirable to customers (Figure 17).

  • Weeds are plants that compete with your crops for space, light, and nutrients. If you raise livestock, weeds might be a feed source, or certain poisonous weeds might be a risk to your animals. To help you identify weeds on your farm, I recommend either Weeds of the Northeast, by Uva, Neal, and DiTomaso or Weeds of the South by Bryson and DeFelice.

    Plant identification smartphone apps are also available, as well as an excellent Facebook group: https://www.facebook.com/groups/156706504394635/
     
  • Different diseases affect plants and animals. If you are growing crops in Maryland, University of Maryland’s Plant Diagnostic Lab is an amazing resource for help diagnosing plant diseases: https://extension.umd.edu/plantdiagnosticlab.
     
  • If you are raising livestock, the best resource on animal diseases is a veterinarian who is used to working with agricultural animals.

    If you are raising chickens and other poultry, UMD’s small flock production website has some great introductory articles and videos on preventing and monitoring for poultry diseases:
    https://go.umd.edu/smallflock

     
  • Invertebrate and vertebrate pests feed on crops and livestock and spread diseases. Invertebrate pests include things like slugs, nematodes, and mites, as well as true insects like thrips, aphids, grasshoppers, beetles, and caterpillars. On outdoor urban farms in Baltimore, particularly troublesome invertebrate pests include flea beetles (multiple species), squash bugs (Anasa tristis), harlequin bugs (Murgantia histrionica), the caterpillars of cabbage moths (Mamestra brassicae), and spotted and striped cucumber beetles (multiple species, can transmit squash wilt disease). In high tunnels and indoor production, aphids, thrips, whiteflies, and spider mites can quickly build up to high populations.
     
  • When it comes to vertebrate pests on urban farms,everyone asks about rats. But anecdotally, what urban farmers have told me is that rats prefer to eat trash rather than vegetables. Rats may feed on fruit crops, particularly melons. In general though, I have found squirrels to be a bigger problem than rats for urban production, not because squirrels eat that much produce but because they appear to obsessively dig up any loose soil, killing small seedlings. An urban farmer named Clayton Williams taught me to use bird netting to exclude squirrels, and I have found that to work well (Figure 18). Mulch can also help deter squirrel digging behavior.
     
    • Deer, gophers, and groundhogs are also important vertebrate pests of urban farms. Excluding deer can be difficult and expensive, especially once they know something delicious is growing on your site. Jonathan Kays of UMD Extension has a comprehensive guide to deer exclusion options: https://go.umd.edu/deerexclusion
       
    • When it comes to livestock, invertebrate parasites are the main concern. Sheep and goats, for example, are plagued by parasites. For more information, see UMD’s small ruminant website: https://www.sheepandgoat.com/
       
    • Fish and other aquaculture “livestock” can also be infected by various diseases and parasites. UMD Extension has a helpful factsheet on aquaculture biosecurity here: https://go.umd.edu/aquaculturebiosecurity

Pest management strategies:

Figure 19: Pest management is an iterative process, in which you build prevention into your farming system, address problems as they arise, and learn how to better prevent those problems in the future. Photo by Edwin Remsberg, © University of Maryland—AGNR Image Library.
Figure 19: Pest management is an iterative process, in which you build prevention into your farming system, address problems as they arise, and learn how to better prevent those problems in the future. Photo by Edwin Remsberg, © University of Maryland—AGNR Image Library.

Ideally, pest management follows a circular sequence of prevention, management, and learning (Figure 19).

What tools you use to prevent and treat problems will vary depending on whether you use organic methods, but the process of preventing, scouting for, treating, and reassessing is important for all growers.

Pest management strategies that urban growers use in particular include

  • using row covers and high tunnels (with netting on the vents) to exclude invertebrate and vertebrate pests;
  • using crop rotation to break disease and insect life cycles (can be challenging in small spaces);
  • removing heavily infested crops and planting something from a different crop family;
  • planting a diversity of crops; planting native plants to encourage beneficial insects such as predators of pests;
  • trap cropping and intercropping;
  • mulching to reduce weed pressure;
  • tarping or using the stale seedbed technique to kill weed seedlings;
  • using insect traps to monitor infestations (be careful with baited traps, which can attract pests more than you want them to).

To learn more about pest management, here are the resources developed by UMD Extension:

For ornamental, cut flower, and greenhouse production: http://extension.umd.edu//programs/agriculture-food-systems/programs/ornamental-horticulture/ipmnet

For vegetables: https:extension.umd.edu//programs/agriculture/program/fruit-vegetable-production/maryland-vegetables

Water management:

Figure 20: Drip irrigation pairs well with mulch to direct water to crop roots while reducing weed pressure. Relatively inexpensive timers are available to automate irrigation through drip or overhead systems. Photos taken by Neith Little at Carroll County office of University of Maryland Extension.
Figure 20: Drip irrigation pairs well with mulch to direct water to crop roots while reducing weed pressure. Relatively inexpensive timers are available to automate irrigation through drip or overhead systems. Photos taken by Neith Little at Carroll County office of University of Maryland Extension.
 

Most urban growers rely on municipal water for irrigation, which can be expensive. This makes using water efficiently especially important. On some urban lots, getting access to municipal water can be a big challenge.

Some growers also collect rainwater, and most growers I’ve spoken with want to. This is one of those practices that makes a lot of sense financially and environmentally, but makes food safety scientists nervous because of potential risks of contamination if rooftops or other surfaces exposed to birds and rodents are used for rainwater collection. Researchers and Extension Agents are working on improving our recommendations for best practices for utilizing rainwater and other “non-traditional” water sources. For now, the best risk management practices recommended are to apply collected rainwater using drip irrigation or

Harvest, post-harvest storage, and food safety:

How you harvest your crops and how you store them until your customers purchase them has an important impact on the quality of your product and on food safety risk management.

For most vegetables and fruits, especially leafy greens and herbs, harvesting first thing in the morning before the day gets hot is a good practice to prevent wilting and increase the shelf life of your produce. Tomatoes are an exception to this rule, because they are so susceptible to fungal and bacterial diseases. Avoid harvesting or otherwise disturbing tomatoes when the leaves are wet from dew or rain, because damaging the leaves when wet can increase the chance of infecting the tomato with a plant disease.

The appropriate temperature and humidity for storing harvested crops varies depending on the type of fruit or vegetable. In general, for optimal taste and shelf-life, cool-season crops like kale and cilantro, need to be kept cool and prevented from drying out while warm-season crops like tomatoes and basil should not be refrigerated or stored damp. Some crops, such as winter squash and sweet potatoes, benefit from a “curing” stage between harvest and eating.

In general, plant diseases do not infect human beings. But human diseases, such as E. coli or Salmonella, can contaminate produce. Basic food safety risk management practices include training anyone harvesting to wash their hands, cleaning and sanitizing tools for harvesting, storing produce at appropriate temperatures, restricting animals' access to places where fresh produce is growing, and waiting 120 days between applying manure and harvesting. To learn more about food safety, see the UMD Extension food safety page here: http://extension.umd.edu//programs/agriculture/program/fruit-vegetable-production/food-safety

 

Summary

Whether you grow vegetables, raise livestock, or culture mushrooms, taking the time to learn more about the topics in this chapter will help you better use the resources available to you to maximize how much you produce while minimizing the impacts of challenges like pests and weather.

Soils, growing media, and nutrient management are the foundation of a farm and understanding them better will unlock your plants’ productive potential. Soil testing for metal contaminants can empower you to know whether you need to use best practices to protect the health of yourself and your customers. Crop rotation is a powerful tool for preventing pest and disease problems and improving the fertility of your soil. Crop planning will enable you to plan your production schedule to meet your marketing goals. Proactive pest management will help you prevent problems in the first place, and deal effectively with pest problems that do arise. Season extension offers affordable tools for protecting your crops from uncertain weather and climate, and growing crops at times of the year when market demand is higher. Harvesting at the right time of day and storing harvested crops appropriately will protect the results of all your hard work, and adopting good food safety practices will protect the health of your customers.

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