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A friend said to me:

Using a little detergent can help revive a potted (or planted) plant that has not completely died but has been under watered almost to the point of death.

I'm dubious; using detergent on a plant sounds like it would kill it rather than revive it. I found this question here which does imply that detergent (or at least some types of detergent) are best kept away from plants in general, not to mention those that are close to death.

Is there any truth to my friend's recommendation?

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    The only legitimate use of soap on a plant I know of is as an insecticide, so it might help if the plant was being attacked by certain bugs - otherwise, not a myth I've heard of before. In most cases if a plant is in deep trouble, you are better off composting it and starting over rather than playing heroic plant nurse. – Ecnerwal Jun 3 '16 at 1:13
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This sounds like one of Jerry Baker's wacky tonics although even he doesn't recommend detergent except for dish detergent aka regular dish soap. A real detergent will likely harm the plant.

While some of his suggestions are odd and I don't think there's much scientific research done on his tonics as a whole there is some merit to a few of his ingredients.

Dish soap contains surfactants and surfactants can help hydrate soils and relieve compaction but only for soils that have become hydroscopic. Some people use baby shampoo instead. However research indicates that it's very rare that a homeowner would have hydrophobic soil and mechanical aeration is better than surfactants. (link to my website)

If you're talking about a potted plant with a peat based potting medium then those can go hydrophobic when they get very dry. In that case a surfactant or wetting agent may help quickly hydrate the potting mix but you could also place the container in tepid water to speed up hydration.

Soaps also contain phosphates so if your soil/plant needs phosphorous it's another way to give it to it but it's not like you can't get phosphorous to fertilize your plant with. Commercial growers tend to use wetting agents when hydrating their potting mixes because it's faster and time is money.

So a detergent like laundry detergent no, it will likely harm the plant. Dish soap and baby shampoo might offer some benefits under certain conditions but you can achieve the same results with other products or methods meant for use on plants.

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  • Thanks so much for going into this detail. Accepted and upvoted! – Tim Malone Jun 4 '16 at 1:29
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Basically when soil is dehydrated below 30%, Fe-containing molecules form on organic surfaces, rendering surfaces hydrophobic. Detergents antagonize this acting as a wetting agent.

But I'd just drop the whole plant into a bath.

http://forums2.gardenweb.com/discussions/1481271/dishwashing-liquid-added-to-plant-water

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