Soap that won't kill plants?

February 28, 2006 8:48 PM

I have a crazy idea involving my washing machine, its outflow, and my garden, but there's a little problem involving suds...

I'm trying to conserve water, and I realized that the pipe connecting the outflow of my washing machine could be redirected to spill out over a patch of my (currently rather bare and boring) backyard. The problem, of course, is that washing machine wastewater still has the detergent in it, and I don't think that's very good for plants. What I'd like to know is if there's a way for this scheme to work - are there plant-safe detergents out there? Preferably ones that won't break my budget?

posted by wanderingmind to home & garden (10 comments total)

you are talking Gray water. A good place to start is fin dyour local co-op and look through their soap section. I am very confident you will find something.
posted by edgeways at 8:53 PM on February 28, 2006

For example... I am sure there are many options
posted by edgeways at 8:55 PM on February 28, 2006

Or just use soap powder.
posted by Wolof at 8:59 PM on February 28, 2006

The main problem is excess phosphorus. Low-P detergent is available in my supermarket, it even says somewhere on the box that it's "safe for gardens". Of course, it's not unusual to divert greywater in Australia (well, increasingly less so). Quite a simple process generally, and quite safe.
posted by wilful at 9:04 PM on February 28, 2006

the soap is not the only issue you need to worry about, the chemicals, dyes, and dirt (generic term) on your clothes could also harm your garden.
posted by crewshell at 11:14 PM on February 28, 2006

In general, water from your washing machine is fine for your grass and flowers and maybe even for your veggies. You could, if no one was looking, just run the pipe out to the garden and let 'er rip, and almost certainly nothing bad would happen to you or anyone else or anything else. But that's not the kind of carefree world we live in now, so read on.

• Check local ordinances. No matter what we say here, the government decides what you can do. Besides, the government has lots of free advice to hand out. Here are a couple of very informative PDF files from California and New Mexico.


• Keep it within boundaries. Regardless of the law, it isn't cool to have your waste water run on to someone else's property. Imagine how you'd feel if your neighbor washed his underwear and ran the waste water directly on to your property. All excess gray water must run directly to the sewer.


• There are lots of opinions on what detergents to use. (For instance, "Soap and detergent ingredients to avoid are sodium, chlorine, and boron...".) Read the government brochures I linked above and try to follow their guidelines.


• It is often said that you should not use gray water on your vegetable garden, but I think this is a precaution more to prevent the spread of disease than it is a worry about what soap might do to your veggies. If your gray water includes water from showers and sinks, there will be lots of stuff (perhaps including various amounts of human spit, snot, blood, piss, and shit) going out to your garden that could conceivably carry disease that could conceivably get on to your veggies and spread to whomever eats your veggies. Using water only from your clothes washer, unless you're washing lots of diapers, would seem to be a different story. Regardless, it may be illegal for you to use gray water, even if it's just from your clothes washer, on your vegetable patch but just fine to use it on grass and flowers.

posted by pracowity at 12:26 AM on March 1, 2006

In Australia you can get a device that diverts outgoing grey water into a storage tank. You go to the pipe outside your house (if you can access it) and insert this rubber thing that looks like an elongated funnel. Outgoing water diverts to whatever container you provide.

Let me know if this piques your curiosity, and I'll see if I can find out what it is called. We have fairly serious water restrictions here. I salute your conservation efforts!
posted by tomble at 12:40 AM on March 1, 2006

In Australia you can get a device that diverts outgoing grey water into a storage tank.

Personally, I think this is where you start the project. Well, first start using a very clean detergent (Seventh Generation comes to mind). But then you probably want to store up the grey water and possibly treat it before applying it to your garden.

You may also need to add a pump to get the water from the washign machine to the sotrage unit. As it is now your washing machine probably only can push the waste water as far as the utility tub. If yoou are going to redirect it outside, you may need more power to get it there. Even if it is a sump pump sort of thing that takes the water from the utility tub.

Here are a few other guidelines I found:

• Apply greywater directly to the soil, not through a sprinkler or any method that would allow contact with the above-ground portion of the plants.


• Root crops which are eaten uncooked should not be irrigated with greywater.


• Plants that thrive only in acid soil should not be watered with greywater, which is alkaline.


• Use greywater only on well-established plants, not seedlings or young plants.


• Disperse greywater over a large area, and rotate with fresh water to avoid buildup of sodium salts.

posted by terrapin at 6:50 AM on March 1, 2006

My family had to divert laundry water to the backyard for a week while our laundry drain was being repaired. The flowers grew so fast out there! We did use less soap (you don't really need that much anyway) so I don't know how that would affect things. The suds also kept aphids away.
posted by idiotfactory at 9:16 AM on March 1, 2006

Many new "green" house building plans call for diverting the shower water. I've always thought this was a smart source of grey water because there is so much water and so little soap. And it's easy to find gentle, non-polluting soap to wash your body and hair.

When I was growing up, my mother had a "suds saver" feature on the washing machine. It came with a drainage pipe that either went into the sink or into the sewage pipe in the wall. Unfortunately it had a tendancy to disconnect itself with the first flood of releasing water. You would hear the "thunk" of the cycle change and you had to run over and hold onto the pipe or else it would disconnect and you flooded the kitchen floor. I was late to the first day of school because we were busy mopping up.

You were supposed to reuse the sudsy water to wash the floor or something, but I don't think we ever did-- it looked too dirty. Oddly enough there was no option to save the cleaner rinse water. I guess back then water was cheap but soap was expensive.

These days I use my floor washing water to water the potted plants. I use only a small amount of mild detergent and the plants like it fine.
posted by Secret Life of Gravy at 11:12 AM on March 1, 2006