Knowledgebase
Soap use outdoors #901575
Asked May 15, 2025, 8:22 AM EDT
I'm planning to repurpose an old potted bench with a sink to create an outdoor place to wash my pots. I will be collecting the waste water in a bucket. I've been told there are soaps that I could use that are safe for the grass, plants, etc. Is that true? If so, please advise the names or the ingredients to look for. Thanks!
Oakland County Michigan
Expert Response
Hello Susan,
A good rule of thumb is to use a biodegradable, phosphate‐free soap made solely from natural fats and oils—essentially a “pure” soap rather than one loaded with synthetic detergents and additives. When diluted and used outdoors, these soaps break down naturally, reducing the risk of harming your grass, plants, or soil.
One popular option that many gardeners and environmentally conscious users rely on is castile soap (a product like Dr. Bronner’s). Castile soap is made by saponifying organic oils (typically olive or other vegetable oils) with an alkali, resulting in a substance that is not only biodegradable and gentle on the environment but also effective for cleaning. Its simplicity and lack of harsh chemicals make it safe, even if a bit of runoff reaches your garden. THIS MEANS DON'T DUMP THE BUCKET OF WASTEWATER ON GRASS, PLANTS, OR THE SOIL – DUMP IT DOWN THE DRAIN.
While many university extension services discuss “insecticidal soaps” (which are chemically quite similar as they are also based on potassium salts of fatty acids) for pest control on plants, the key takeaway is that the safest products lack the extra harsh components found in many conventional cleaners. These additives—often present in industrial detergents—can cause unwanted damage to soil microbes and plants, even when used in diluted form. DON'T USE THESE SOAPS. More information at this link:
Insecticidal Soaps for Garden Pest Control | Home & Garden Information Center
Insect Control: Soaps and Detergents - 5.547 - Extension
Before you choose a soap, check the label for indications that it’s biodegradable, phosphate‐free, and free from unnecessary synthetic additives. Even with a “green” soap, it’s wise to use it in a well-diluted form (commonly around 2–3% concentration) so that any incidental contact with plants or grass won’t have adverse effects. Also, consider rinsing your pots thoroughly after washing to minimize soap residues reaching your garden. ALSO DUMP THAT WATER DOWN THE DRAIN, NOT ON GRASS, PLANTS, OR SOIL.
I hope this helps!
