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Yesterday I was talking to my neighbor, and he was telling me he was cleaning the trim on his house with Dawn (dishwashing detergent used in the US) mixed in water. I thought I read somewhere that Dawn can damage or kill plants. Is this true? I was thinking about trying this myself, but have shrubs and flowers under the trim I want to clean.

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I've used sudsy dish soap such as Dawn before to combat insects such as aphids and it is quite effective and the one I used (it wasn't Dawn specifically) was biodegradable and that's important to me.

The key to using Dawn or anything (siding cleaner, bleach, etc.) around plants is that you need to lower the concentration of the chemical low enough that it doesn't harm the plants. A number of years ago I cleaned my siding with a soapy liquid something like Dawn with bleach in it. In preparation for this I thoroughly soaked the vegetation with water - I DRENCHED it to be sure - and then cleaned the siding as prescribed by the cleaner, then I hosed all my plants down again, ensuring that any of the cleaner was highly diluted.

Plants are pretty resilient and tend to fare well under some extreme conditions. A little insurance in the form of a good hosing down before/after the cleaning should be all they need.

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I use Dawn to control whiteflies on tomato plants all the time. If the concentration gets too high it can destroy all of the leaves, but in small amounts it has proved harmless.

  • I have also used Dawn to control whiteflies, if you don't go overboard it is fine for the plant and won't kill it. This has also been discussed here wiltedleaf.com/678/… – Scott Jun 13 '13 at 3:50
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    Could you add some detail about how much you dilute the Dawn before using it on the plants. The phrases "too high" and "small amounts" won't help anyone that reads this answer in the future. – Niall C. Jun 13 '13 at 14:12
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    One tablespoon per gallon is as far as I go. I think I used three on a hot day with blazing sun and it turned out very bad. Every leaf on my tomato plants fell off. I think waxy leaves are more tolerable. I found this on the web and it has served me well. It even killed a major scale infestation on a ficus for me. Amazing. essortment.com/homemade-insecticidal-soap-recipe-51604.html I recently used this on some boxwoods and it killed the adult phyllis very well. – Evil Elf Jun 13 '13 at 14:53
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    I've used a mixture of 2 tsp. dish detergent (don't remember brand name), 2 tsp. neem oil, and 1 gallon of water for pest control. I apply it to the foliage using a garden sprayer. The plants don't seem to mind, and it helps keep the bugs away. – Doresoom Jun 14 '13 at 13:58
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I have been using detergents like Dawn dish soap to wash my vehicles and even went as far as using bleach water to clean the siding of my home right next to a big hedge bush. So far I haven't seen any ill effects from doing so. Of course I do use things in moderation, a little Dawn as well a little bleach goes a long way in a bucket of water, but I guess if it bothers you then maybe a bottle of "Simple Green" would be a great thing to keep around the house.

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YES!!! Unfortunately it has taken me nearly killing two hibiscus plants to figure it out. I used Dawn diluted in a small spray bottle when I noticed aphids on my first plant. Within a couple of days all the leaves began to yellow and die off. I did not make the connection, however, until several weeks later I noticed aphids on the other plant and repeated the procedure. Of course within two days all those leaves began to yellow and fall off. I used approx. 2 Tbsp. dawn with an 8 oz spray bottle.

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    That is a very high concentration, this makes sense. Welcome to the site! This is a helpful answer, from personal experience. – J. Musser Aug 23 '14 at 3:49
  • Two tablespoons is 1 ounce, so that's a 1 in 8 dilution, far higher than you'd use for normal dishwashing purposes. No wonder your plants almost died. – Niall C. Aug 23 '14 at 3:51
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the soap really harm plants, but actually if you will make soap out from the wood ash, it will never harm the plants and it can kill pests that are destroying your plants.

for now, that's our investigatory project... but as soon as it will be finished, I will share it to you guys!

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    Please add more details about why soap will harm plants. Your answer doesn't really answer the question. – kevinsky Jul 29 '14 at 10:11

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