Soil Solarization

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It’s hot, spring and summer crops are coming to an end, and the transition to fall planting is in the horizon. If you live in a southern climate like we do, now is the best time for soil solarization. Solarizing unused garden beds or areas cleared by harvesting will help rid the soil of plant funk, otherwise known as diseases, pesky weeds like crab grass, and destructive parasitic root knot nematodes. It’s an especially useful process in tomato and chile beds which are commonly known to harbor wilt disease, such as verticillium and fusarium. By laying out a sheet or tarp of clear plastic over the bare garden patch for 4-6 consecutive weeks during the hottest months, which is usually August and September in Southern California, the sun will heat the top foot of soil up to 140°F, killing bad pathogens, diseases, weeds, and insects. Yet, soil nutrients and beneficials will be able to withstand the heat. What a great way to use the sun as an all-natural, organic pesticide!

Here are some simple “how to” steps:

  1. Weed and clear the area of any leftover plants and roots by cultivating the soil to get it ready for the next season.
  2. Level the soil surface.
  3. Irrigate the soil down to at least 12-18 inches in order to increase heat conductivity.
  4. Cover the area with clear 2-4 mil painter or construction plastic, or a clear plastic tarp. Make sure the edges are anchored with rocks, soil, bricks, etc. to keep it completely down during the entire length of time (4-6 weeks). In our raised garden beds, we stapled the plastic over the edges and corners of the wood boxes and placed a couple of bricks on top to keep the plastic right on the soil.

In the meantime, begin planning and seed starting fall crops like beets, cauliflower, broccoli, kale, lettuce, peas, and more. At the end of the solarization process, your soil will be ready, like a fine stew. Spice it up with organic fertilizer and a pinch more of compost, and your garden area will be fine dining for plants. Good luck and happy planting!

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