I'm thinking it couldn't be too good, there are tons of chemicals in those.....but how about doing what they did in the old, old days - a "spit bowl" of some sort (with a cover of course!) at the bedside??

As harsh as it feels to the human mouth, Listerine might be fine for plants (not supporting Pfizer, but it's the only brand I could get the ingredient list to quickly). See below.

Most of the active ingredients are actually herbal derivatives (from thyme oil, eucalyptus oil, peppermint oil; methyl salicylate is similar to asprin). The benzoic acid and sodium benzoate in the inactive ingredients are probably not the best for plant health, but are in as preservative and probably at low concentrations. Poloxamer 407 is a surfactant and shouldn't be directly toxic but may affect the soil (surfactants are used environmentally to help 'wash' contaminated soils). HOWEVER, I don't know what the effects of alcohol on plants would be. That'd be the ingredient of concern.

Might be worth experimenting with one of you least favorite plants.

LISTERINE®
Manufacturer: Pfizer Consumer Healthcare

Active Ingredients: Thymol 0.064%, Eucalyptol 0.092%, Methyl Salicylate 0.060% and Menthol 0.042%.

Inactive Ingredients: Water, Alcohol 26.9%, Benzoic Acid, Poloxamer 407, Sodium Benzoate, and Caramel.

With the major ingredient as alcohol can't see where this is going to hurt plants.
I use straight alcohol for dealing with pest on houseplants.

Wouldn't the alcohol kill off some of the living microorganisms in the soil? It's a disinfectant. Wouldn't want to wipe out your microherd with a mouthful, eh?

The amount of mouthwash is very small compared to the micoherd in the soil-it isn't going to hurt anything.

I used mouthwash to kill ants that took up residents in my green onion bed and it did not hurt the onions at all.

My husband uses Listerine in a lawn concoction he got from Jerry Baker. It actually helps the lawn!

Yes it absolutely will significantly hurt the soil microherd. As was mentioned alcohol is an antiseptic. Thus by definition it kills bacteria. Bacteria are what give life and structure to soil. And since there are 10-20 layers of invisible bacteria and fungi living on the leaf surfaces, too, spraying plants with alcohol is disturbing the plant's ability to fight off disease.

How about a spitoon?

BF and I started to wonder about the old Listerine's effect on our septic system....will it harm the necessary bacteria living in there? Dentist orders for us both to do Listerine rinses at least twice a day. I usually go outside and spit it out on weeds in the morning. Can't tell that it's harmed any weeds where I've been spitting.

Jerry Baker, radio gardener, has used mouthwash as part of his hose-end sprayer recipes with great success. It does not hurt plants, but it does kill microbes in the soil.

Bottom line: I don't think it will hurt the house plants and it should keep mold and mildew from forming in the soil.

Re: septic tanks

I think anything you put down the drain will hurt a septic system's bacteria. Including mouthwash. Alcohol will kill some bacteria (not all in the septic tank) and slow the process. Same thing with drain openers, and cleaners with bleach and other chemicals (like cleanser with bleach).

I've been living with septic systems for 25 years. Rinsing you mouth a couple of times a day with Listerine or doing a few loads of wash with bleach added won't make a dent in the microbial population in a septic system. Dumping gallons and gallons of the stuff into the septic might. Just like a few mothfulls of alcohol containing mouthwash spit into the soil. Immediately kill microbes? Maybe a few. Alter the overall population and ruin the garden? Not likely. Lets be realistic.

Realistically speaking (or writing), every bacterium or fungus that gets soaked in 25% alcohol will die. If she's spitting into the same potted plant all the time, the soil will lose all its life and will require continual sterilizations to prevent the "mold and mildew" from forming. If the soil was left alone or organically fertilized, it would prevent mold and mildew by itself.

The Jerry Baker concoction has very little sterilization effect because the small amount of mouthwash is diluted in 15 gallons of water and they sprayed through the air where the alcohol will evaporate before hitting the ground.