Soil Tests
Before starting a garden, it is essential to test your soil for contamination, even if you do not plan to grow an edible garden. If students are going to be interacting with the soil, test for heavy metal contamination, such as lead. Children are particularly susceptible to the long-term effects of lead poisoning, which stems from ingesting materials that contain lead. Often, in gardens this risk is associated with ingesting lead-contaminated soil on or around produce that is not thoroughly washed. This guide from the University of Maryland contains more information on soil lead risks and mitigation.
The University of Delaware Soil Testing Program will conduct affordable soil tests. Your soil test will provide recommendations for whether you and your students can safely plant or work in the area. If not, explore creating a container garden. On some sites, a raised bed garden filled with purchased soil may be most appropriate if existing soil is degraded, compacted or contaminated. While raised bed gardens often have a higher initial cost than tilling the soil directly, they can even be built on asphalt or concrete. If contamination is not a problem, your soil test report will provide recommendations for improving your soil.
Water Tests
If you plan to irrigate your garden or wash produce from the garden to prepare for consumption, test the water from the tap that you will use to do so. Tests should show if there are elevated levels of heavy metals and microbial contamination.
Water test results may not be straightforward. Your water test results will tell you if your water meets drinking water standards. If it does not, do not drink the water or use it for washing produce prior to consumption. Use a source of potable water instead. Unfortunately, there are currently no clear regulatory guidelines for what levels of lead are considered safe to water your plants (irrigation water). The Farm to School team has spoken with scientists and other urban school districts to understand best practices for approaching this issue. Based on this information, we have developed the guidelines below.
The health risk of lead comes from ingesting materials that contain lead, not from skin contact. Generally, water tests for lead are far more sensitive than soil tests for lead, measuring concentrations in parts per billion (ppb) rather than parts per million (ppm), the metric used for soil. Thus, if your irrigation water has elevated lead levels, there is minimal risk that it will significantly add your soil lead levels over time. Michigan State University researchers have explored this specific issue, and this article contains their findings: water with 15ppm of lead does not appreciably add to soil lead levels. However, it is still very important that water with elevated lead levels is used with care in a school garden setting to avoid accidental ingestion. If your water test results show lead contamination above the drinking water standard, follow these best practices:
Never drink or wash produce with the water. Always use a source of potable water instead.
Do not allow students to play in the water.
If another source of irrigation water is available, consider using that instead.
If using the water for irrigation, allow the spigot to run for at least 2 minutes before using it to irrigate the garden. Before using the spigot for the first time of the season, allow the water to run for a full 10 minutes before use. These measures help to flush lead that may have accumulated in the pipes.
Take a precautionary approach: have adults irrigate the garden rather than students.
If using water with lead levels above the drinking water limit to irrigate your garden, retest your soil lead levels annually.
Document all water test results and share the information with all school staff involved in the garden. Be sure that all adults who work in the garden are aware of these best practices.
When taking a water sample, it is important to use proper techniques for accurate results. If you are taking a sample from a hose spigot:
Allow the spigot to run for 10 minutes prior to sampling if it is the first time you have turned it on in this season.
If the spigot is in frequent use, allow to run for 2 minutes prior to sampling.
Other Garden Safety Resources
The University of Maryland Extension offers this Food Safety in your School Gardens guide.
Stay updated on the latest research on urban soil safety by following the Johns Hopkins Center for a Livable Future’s Safe Urban Harvest Study.