Urban Soils

There is a free soil testing service that Urban Soil Institute provides on Governor’s Island with some samples from the garden. A few years ago I tested soil near my house in Jersey City. Of the heavy metals that were tested, the only one that had a moderate level of concern was lead (Pb) with the highest sample reading at 315 PPM (EPA standard). Lead is naturally occurring in our environment at low concentrations. However, during the 20th century, lead-based house paint and leaded gasoline introduced toxic levels of lead into the ground that still remain today, especially in urban areas like ours.

Dealing with contaminated soil is a major part of urban gardening and we want to make it a bigger priority to educate garden members about it. Fortunately, there are many resources out there. The best local information comes from the cooperative extension program at Rutgers, here is their guide for dealing with lead: https://njaes.rutgers.edu/fs336/

GreenThumb, the community gardening division of the NYC parks dept, gave a great webinar on gardening in urban soils at this year’s GrowTogether conference, here is the recording: https://www.youtube.com/watch?v=VPEtT8eK1mY

Here are the biggest things to keep in mind:

• It is much more likely to be exposed to lead and other heavy metals from dust particles than ingesting them through edible plants. This is why it is very important to thoroughly wash any plants you grow in the community garden before eating. You should wash your hands after gardening and avoid tracking dirt in your house with the shoes you wore in the garden. It is also important to keep the dust down in the garden as much as possible by mulching.
• Lead affects children more than adults so be mindful of your children’s exposure to direct earth while in the garden. We have added a thick layer of mulch in the children’s garden recently to help with this.
• Some edible plants are more likely to uptake lead than others. Tomato, sweet corn, squash, eggplant, or peppers are the least likely vegetables to uptake lead. Root crops and leafy greens are the most likely to contain lead.
• Keeping a neutral pH in the soil between 6.5 and 7 helps minimize the uptake of lead into plants. A sample tested from the center of the garden last year had a pH of 6.6
• Amending compost and mulch to the soil helps dilute the concentration of lead, however, it is important to note that it does not remove lead from the soil and only makes it less bioavailable.

If you are concerned about the levels of lead in the soil you may consider growing some or all of your edibles in containers or pots on top of your plot. Here is a guide on how deep a container should be to grow certain edible plants: https://www.gardeningchannel.com/how-deep-should-a-container-garden-be/. It is best to use good quality topsoil or potting soil mix for containers. Remember that soil in containers will dry out faster than in the ground so they must be watered more frequently.