Urban Gardening Considerations

Along with the trends of buying local food, buying organic, etc., there seems to be an increasing interest in the ultimate local food source – a garden. This includes in urban areas. Urban gardening is a great way to save money on food, a great source for fresh vegetables – especially in “food deserts”, and an easy way to introduce kids to where the food on their plate comes from. However, there are a couple potential obstacles you should consider first before starting your urban garden.

"Graze the Roof" by Sergio Ruiz
“Graze the Roof” by Sergio Ruiz

First, in urban environments the possibility that soil could have been contaminated with heavy metals, petrochemicals, etc. is pretty high, especially in older neighborhoods. Lead, which was once a common additive to gasoline and paint, is a common contaminant in urban soils.  and can be absorbed by the roots of the vegetables you grow. Because of this, that lead can eventually end up in the food on your plate. Most lead poisoning comes from ingesting lead (like eating lead paint chips…), so it’s important to know that the soil you’re using for your garden is safe. You should take some soil samples and send them to a lab in your state that can test for heavy metals like lead. Usually the Land Grant university in your state (if you’re in the US) will have a soil testing lab where these tests can be performed for a nominal cost. Other forms of contamination are possible as well, such as chemicals from cars, asphalt , laundry-mats, etc. These chemicals are more difficult to test for, so your best bet is to find out the history of your garden plot. These records should be available from your local city government, perhaps even online. Read more about contamination in this post.

Second, urban soils are often compacted from foot, car, or perhaps machinery traffic. Compacted soils make it difficult for plants to grow, mainly because the plant roots are not strong enough to penetrate the compacted soil, and thus cannot gather enough water or nutrients for the plant to survive, let alone grow and produce vegetables. Compacted soils are especially common in newer housing developments where entire blocks of houses were built around the same time. The construction companies often remove all of the topsoil prior to building the houses. The soils are then driven over by construction machinery and compacted. Then sod is laid directly on top of the subsoil. This makes for soils with very poor growing conditions for both lawns and gardens.

A good alternative for areas with either contaminated or compacted soils is to use a raised garden bed with soil that was brought in from a reliable source. You can buy bags of potting soil from a local home and garden supply store, but a more economic alternative is to have a trailer full of topsoil trucked to your raised bed. When you build your raised garden, be sure to use untreated wood. Some of the chemicals used to for pressure treated lumber are designed to kill fungi that break down wood. These chemicals, some of which contain arsenic, can leach out of the wood and into the soil used for your veggies! However, untreated wood, though it might not last as long, will still last for decades and is probably cheaper anyway. There are lots of great designs and how-to sites that show you how to build a raised garden bed. Here’s an extension bulletin from Washington State University on raised bed gardening. The raised beds shown below are from when I first installed them in my community garden plot in Manhattan, Kansas. One is now a strawberry patch (the border helps contain the strawberries to a defined area), and the other is used for mostly cold season crops.

This image shows two raised garden beds with freshly added soil and surrounded by straw in a garden plot.
Raised garden beds in Colby Moorberg’s community garden plot.

Space is also another consideration. If you don’t have the space for a garden or a raised garden, then perhaps you need to think outside the box (raised garden pun intended) and consider container gardening. Container gardening is exactly what its called – growing ornamental or vegetable plants in containers. Containers can be traditional plant pots, buckets, plastic totes, or any other container with an open top.

The advantages of container gardening include:

  • Containers can be arranged to optimally use the space available, or rearranged if you like to mix things up sometimes
  • Potting soil can be used, and can be trusted to be lead/chemical-free
  • Work can be performed on a bench, thus avoiding working on your knees
  • Containers can be arranged to provide decoration for your outdoor space
  • Many objects found around the house can be cheaply converted into decent containers
Vertical Pallet Garden. Photo by Heather Foust

Vertical gardening is a version of container gardening that uses your available space  efficiently. Much like using shelves to save space inside your home, vertical gardens use shelves, stairs, racks, etc. to make use of vertical space. The options for vertical gardens are only limited by your imagination. Here are a few extension bulletins on vertical gardening from Tennessee State University and the University of Nebraska.

The main disadvantage of container gardening is that you’ll likely have to water more frequently, but there are strategies to overcome that problem – see my prior blog post about saving water with container gardening. Another good resource is the University of Illinois Container Successful Container Gardening website.

In summary, the biggest obstacles to urban gardening are soil contamination, soil compaction, and space limitations. I’ve given you a few good alternatives to overcome those issues. Also, be sure to fertilize appropriately, lime as needed, and make sure the plants that you pick are appropriate for the sunlight that’s available. Your local garden supply store or extension agent can help you with suggestions on those issues.

If you know of an urban gardening obstacle that I didn’t address, please leave a comment and I’ll see if I can help out.

Happy digging!


This was originally posted on Colby’s soil science blog, ColbyDigsSoil.com. Some edits, updates, and adaptions were made for this post.

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Colby Moorberg

Colby is an assistant professor of soil science in the Kansas State University Department of Agronomy, and is a Certified Professional Soil Scientist (CPSS). A major focus of his research is root ecology - studying how soil properties influence root development, and how the presence of roots impacts soil properties. He grew up on a small farm in Iowa, and has since researched soils in Iowa, North Carolina, Alaska, and Kansas in both agricultural and natural ecosystems. Colby and his family spend their free time gardening some plots at a community garden in Manhattan, Kansas. Colby also enjoys growing hops and other herbs for ingredients for homebrewed beer.

13 thoughts on “Urban Gardening Considerations”

  1. Treated lumber has not contained arsenic in it since 2003, new treated boards are safe for using in raised beds. Also wood will not last years and years in many climates we only get a couple of years out of untreated unpainted wood.

    1. What Becky said. Unless you are re-purposing old lumber, this is a non-issue. Untreated wood lasts at best a year in my climate if it is in ground contact.

      Raised beds are not a solution to contaminated soils, unless they are very high and have an impermeable barrier that won’t degrade or get holes poked in it in a few years.

      Building raised beds is not a cheap project, especially not of a durable quality. For those on a budget, re-purposed containers are a better bet. Home supply companies and landscapers often send nursery plant containers to recycling. These can still be recycled after being re-used for a couple of years until they crack and fall apart.

    1. Thanks, Amy. Your mound of [soil] is a fine alternative. However, that might not always be an option in urban areas discussed in this article. As for the extension article on treated lumber, treated lumber is fine if people read the labeling and confirm it was not treated with CCA. There are still CCA-treated products on the market, so be sure to read the label.

  2. Welcome to the blog! It always makes me happy when an urban garden post appears. My question is on filling the raised bed. Would gardeners use bags of “garden soil” instead of “potting soil”? I am asked this often, so want to be sure I’m going correct advice.

    1. Thanks, Stefanie. And thanks for the question. Generally, garden soil has more mineral matter. This is good in that the minerals will maintain soil volume over time, while the organic matter can decompose and cause loss of volume over time. For that reason and give the two choices you give, I’d go with garden soil.

      For my raised beds I included in the post, I used a mixture of topsoil from the garden plot and compost from the city’s industrial scale composting facility (which is provided for free to gardeners in my community garden). If the compost came from an industrial scale composting facility, the temperature at which the compost heats up is enough to kill off most pathogens, though some seeds can survive these temperatures so weeds are still a possibility. Residential compost piles generally don’t get hot enough, enough times, so backyard compost may still harbor pathogens. The topsoil I used surely contained weed seed… if I didn’t want to weed, I wouldn’t have a vegetable garden in the first place. That said, nearby topsoil would not be an option in most urban settings. However, topsoil can be trucked in from other areas. If you want to go this route, take the time and have it tested before you add topsoil trucked in to the raised bed. For large volumes, I’d go with a mix of trustworthy topsoil and compost.

  3. We need to discipline ourselves not to use the term “potting soil” – there is no such thing. Nursery customers are confused by this. Bagged mixes in nurseries are (should be) labeled container mix, potting mix, growing mix, or planting mix. It’s all peat mixed with “forest humus” or fir bark fines, bits of ground up wood and various other additives. But it’s not soil, even if our customers think it is. It’s meant to be used in pots or containers, not raised beds. Even if harvesting from peat bogs was sustainable, using peat-based potting mixes is not $u$tainable in the backyard vegetable garden! Square foot gardeners should be aware that the newer editions of Bartholomew’s book advocate the use of ‘Mel’s Mix’ which is one part each of vermiculite, peat moss and compost. No soil there. As a soil scientist, can you tell me how long before this would be considered soil or, as we like to say for clarification, dirt? 😉

  4. If I may ask a question or three…

    Where can I find some good information on how to apply lime in different garden situations?

    I know it’s important to have soil tested and follow recommendations for a garden plot or flower bed, but what if l’m planting a tree or shrub? Just add lime to the planting hole? Apply it to the entire area where the roots will spread?

    And how often does lime need to be applied? Does the soil need to be tested periodically, or is the effect of the lime long-lasting?

    During the past year I have been planting a woodland garden under some large yellow pines. (I’m in Georgia.) The soil pH is about 4.5. I’ve been spreading a cup or two of fine pulverized limestone around each tree or shrub after planting. Is this adequate?

    Thank you for helping educate us gardeners.

    1. Hi Alfred –

      Sorry for my late reply – COVID19 has just escalated my email and online work load! Anyway, you should never add anything to the planting hole but the roots, water, and whatever soil came out of the hole. Adding lime is at best a temporary solution to low pH and it’s wiser to select plants that tolerate your soil’s natural conditions. As long as you are choosing trees and shrubs that will grow in your climate, you don’t need to do anything to the soil other than mulch well with arborist wood chips.

  5. Beware that some city composts have high levels of heavy metals, especially if they contain sewage sludge. They should have an analysis that you can see to check what the levels are.

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