Answer: You have a number of options. You can use a vegetation killer such as Noxall or Casoron to kill all vegetation in the area, or you can solarize the soil, or you can use an organic herbicide. To solarize soil, you need to start during the hottest part of the summer, and leave the plastic in place for up to 3 months to kill disease pathogens and weed seeds. Start by smoothing out the area (removing sod, plant debris and rocks), moisten the soil, lay a 4 mm to 6 mm thick sheet of clear plastic over bare soil, and seal the edges of the plastic with rocks or soil. This will naturally heat up to over 140 degrees F, which kills most pathogenic organisms in the top 4-8" of the soil, depending on soil type and temperatures. An easier method is to apply a corn gluten-based herbicide. Gluten is a by-product of corn processing, and has been used in livestock feed, but researchers recently discovered that the gluten includes an enzyme that kills germinating seeds. And to top it all off, corn gluten provides nitrogen to the soil as it breaks down. Nature is amazing, huh? For added measure, after treating the soil and prior to spreading tanbark, put a weed barrier cloth down to be sure nothing sprouts up through the material on the playground. Good luck!
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