The Q&A Archives: Killing Weeds

Question: I have just dug up an area along my front walk to plant bulbs for next year. The soil is pretty good and drains quickly; the problem is that weeds love it. I have had trouble growing grass there because the weeds are so bad. Now that I've pulled out the suface weeds and turned the soil, how do I kill any remaining weed seeds? I thought I read somewhere that putting plastic over the area for a couple of days would heat up the soil enough to kill any seed reamining. If this is true, do I need clear or black plastic? The spot gets all the afternoon southern and southwestern sun it can stand.

Answer: 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. You'll find these products in gardening catalogs. 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? Good luck!

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