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Soap as Plant Food

Howdy You’ll,

We often have bits and chunks of what’s left (mostly used up) of bars of soap in our soap dishes (sinks, shower, tub etc.) over the years, I’ve seen rich plant (mostly grass) growth in areas where grey water runs out on to the ground (e.g. mountain cabin). I know that plants like potassium but as for all the other stuff in soap, I don't know.

For example, we often use Irish Spring Aloe and here is a list of all the monkey business in it:

Soap (sodium tallowate, sodium cocoate and/or sodium palm kernelate), Hydrogenated Tallow Acid, Petrolatum, Glycerin, Coconut Acid, Sodium Chloride, Fragrance, Polyquaternium-6, Aloe Barbadensis Leaf Extract, Pentasodium Pentenate, Pentaerythirtyl Tetra-di-t-butiyl Hydroxyhydrodrocinnimate, Titanium Dioxide, Chromium Oxide Greens.

I'm also wondering about Dish Soap (in bottle) etc.

There are some salts and acids in this stuff but I think only in minuscule proportions so they probably won’t matter.

Does anyone have any ideas e.g. formulas, methods etc. to make fertilizer with leftover soap?

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Super Green Thumb
Posts: 25279
Joined: Sun Feb 15, 2009 6:04 pm
Location: TN/GA 7b

Re: Soap as Plant Food

As you noted, there is little of nutrient value in soap, therefore it is not a good basis for fertilizer.

I have seen recipes for fertilizer containing liquid soap: ... cipes.html

but the other ingredients in the recipes, like beer, ammonia, molasses, provide the nutrients. The soap is just there in its role as a surfactant, to help everything else sink in to the soil.

NOTE: That is liquid soap NOT detergent. Much of what is sold as dish "soap" is actually detergent, which can kill your plants.

If plants do better in grey water areas, that may just be from the extra water and perhaps there are nutrients, like kitchen scraps, in some of it.

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