A 10-12" raised bed on top of it wouldn't hurt it and would keep most of the roots out of it but I wouldn't be tilling up the ground for an in ground bed.

Dave

Not knowing how old the system is or what happens when it needs digging up would make me reluctant. But certainly you can.

It depends a lot what is in your greywater. We use biodegradable detergents (and use about half what they call for), and use the dishwasher only every few days. In fact, best to avoid detergents that have a lot of salt and toxic cleansers (e.g. boric acid). Be aware that most detergents are pretty alkaline. For that matter, avoid softened water entirely, which has a lot of salt in it. I never put our greywater on vegetables, but it spills out in a bed that is taken over with oriental jasmine groundcover. It looks terrific.

Depending on where you live, it is against building code to water vegetables with grey water. I suggest you check with your city to see if it is allowed.

There are quite a few previous discussions here about this topic that the search will pull up for you if you want a wide range of opinions. Just search for 'garden over septic'.

Dave

I'm not sure that gardens over septic are relevant here (though some municipalities do casually declare grey water to be septic outflow). Grey water is what comes off of laundry, dishes, showers and sinks. The septic hazards are totally minimal compared to a true septic field that comes off of toilets. Then again, I've always wondered what some people wash off of themselves, their clothes, and their dishes that might make that wash water septic. To the extent that stuff is truly nasty, one would want the grey water outflow to be deposited directly on soil, and not made into a mist, where it could "infect" unsuspecting people.

My understanding is that building codes regulate what can be built into a building. But no one is going to cite you for hauling pails of bathwater outside into the garden. From a gardening standpoint, the main issue is what's in the water that could be hazardous to the plants.

I built my 80 foot by 50 foot garden over an old septic field that had not been used in 3 years. That was 10 years ago and have never had an issue. I do use raised wood beds.

I think it is relevant if for no other reason than the issue that crop roots can create with the system. That's why the raised bed option works better.

Plus "graywater system" means different things to different folks in actual practice vs. theory. But it is still part of a household's septic system. That means there needs to be ready access to it, things in it that plants may not tolerate much less benefit from, that it is usually seated more shallowly, it is somewhat subject to codes in some locations, and bottom line is less-than-ideal for a garden location.

Leach field gardening discussions

Dave

*facepalm*. Yes, it actually can be against state, municipal or local law or code to water your garden with your old bath water. Up until very recently, that was true for CA and WA. Just trust me, it's my job to know. For instance, did you know that in Nevada it is illegal to collect rainwater from your roof to use in your yard? Yes, really. So, make sure you contact the local authorities and check if your plan is compliant with the local regs. The law for your area could say that you cannot have your grey water in your yard. Yes, the government can do that, that's how all of this works.

Well, my point about relevance was that if you really know what's in your greywater, you're certain that plants should be able to tolerate it, and that it isn't a septic hazard, conversations about how to manage gardening over what is essentially sewage flow in a septic tank drainage field doesn't really contribute a lot. If I am careful about what is in my greywater, it's hard to understand how its use could be disadvantageous for vegetable growing. As I keep saying, it's really about what is in your greywater.

Thank you Marianne. That is very interesting about regulations against using greywater. I guess I was only vaguely aware of that. That is certainly a more pertinent issue. It must be a matter of trusting the homeowner to know what is really grey and what is not, and some municipalities don't. As in, how dark a shade of grey. Now, I can imagine that stuff that comes out of dishwashers and clothes washers could, under some circumstances, when used by environmentally clueless folks, be truly environmentally hazardous waste. Now, how is it justified that rainwater collection from a rooftop is illegal in Nevada? Seems to me that if you don't collect it, it's just going to end up in the soil anyway. That regulation is about timing, rather than pollution.

The municipal water authority has the right to the runoff from the rain so it can go into Lake Mead and if you interfere with their right to their watershed runoff, you're in big trouble. You can't even have rain gutters on your house in Clark county and I'm sure they'd never let you keep & use your grey water. After all, it is their water.

Water regulation is serious business. Even if you own your own water rights, you still may not pond or make use of the water however you want. The local governments have every right to regulate it for health & safety reasons (imagine someone with cholera showered and then used it in the garden and kids played in it...) and because of the intense amount of water rights laws. Many municipalities specifically prohibit the use of grey water on edible crops (Pima County, for instance) and will only approve a system that waters non-edible landscaping.