Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

Is my soil safe for growing vegetables? Can I test for lead?

Growing fruits and vegetables in home gardens is gaining popularity again as people search for ways to eat healthier, be “greener”, and stretch their food budget during tough economic times. But, did you know that the history of a plot of soil can affect the quality of the food produced? The presence of lead and other heavy metals in soil is something to consider, especially in areas that once supported industry that contributed to soil contamination with those substances. Even sites where old houses used to stand can potentially contain soil contaminated with lead from pre-1978 lead-based paints. Areas that were once bustling with traffic and equipment fueled by leaded gasoline are of concern as well because soils soaked up airborne emissions from those activities.

Before you panic and abandon your entire vegetable gardening plan, use this 3-step process to ease your mind about growing your own healthy, delicious fruits and vegetables.

  1. Research the history of your property. If your land supported any of the following, have the soil tested for lead content.
    • Smelters
    • Tailings from metal and ore mines
    • Fossil fuel-fired electrical plants
    • Cement factories
    • Gas stations
    • Houses built before 1978

How much lead is considered safe in soil?  Opinions vary on what constitutes a safe level. Some crops (leafy ones such as lettuce and cabbage and root crops such as carrots and beets) come in closer contact with soil and are much more likely to absorb contaminants. To be on the safe side, if a soil test measures 300 parts per million (ppm) or higher, do not use it to grow vegetables.

  1. Lead is the most likely heavy metal that may be present in St. Louis soils, but others such as arsenic, nickel, cadmium and chromium are possibilities as well. If, in your research, you find that there was a pre-existing possible contaminant for any of these heavy metals, have the soil tested for those as well.
  1. If you are unable to determine the history of your property and/or don’t wish to go to the trouble and expense of soil testing, building a raised bed garden may be the easiest solution of all. Lead and other heavy metals do not move around in soil, so building a garden on top of the existing soil and filling it with uncontaminated soil will allow you to avoid any heavy metals that might be present. Your raised bed should be at least 12 inches in depth (15-18 inches is even better). Be sure to lay a barrier (mulch, gravel, pavers, fabric, etc.) between your raised bed and the existing soil to keep the soils from mixing together.

Raised beds offer quite a few other advantages over in-ground gardens.

Testing for heavy metals cost about $25 each in 2010. Call for current prices.

The following laboratories provide soil testing services for lead and other heavy metals:

S.G.S. Alvey Laboratory, 1511 Main St.,  Belleville IL 62221 (618) 233-0445
St. Louis Testing Laboratories, 2810 Clark Ave., St. Louis MO 63103 (314) 531-8080
Missouri University Soil and Plant Testing Lab in Columbia, MO (573) 883-0623