Answer: As long as you're using dishwashing soaps and detergents, you are generally safe, says Robert Kourik, author of Gray Water Use in the Landscape. What you must be careful to avoid are the harsher cleansers containing bleaches or boron. Even mild soaps can damage the leaves of plants, if the concentration of these substances is high. To be very safe, keep the water from splashing on the leaves. Another reason to pay attention to water placement is possible bacterial contamination of the edible portions of plants. I try to keep the water away from root crops like carrots, beets or onions if it's close to harvest time. If I'm watering lettuce or beans, I keep the spout of my watering can close to ground level, says Kourik. On vertical growers like corn and pole beans, and on ornamental plants, flowers and fruit trees, you can apply the water safely any way you want. Many ornamentals may like the phosphates in detergents, which act as fertilizers for the plants. Since dishwater tends to be slightly alkaline, use it sparingly on acid loving plants such as blueberries and azaleas.
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