Gardening next to a septic drain field

April 5, 2023 9:57 AM

I just learned that my neighbor's septic field goes right up to the property line, right next to where I've planned a bed for herbs and veggies. Unfortunately it's one of the only sunny spots on the property, so I really want to be able to use it. How risky is this, infectious disease-wise?

Obviously any chance of getting e.coli or worse (whatever kind of contamination can come from a septic field??) from my own garden is not great. But what if they're herbs that I'd be boiling for tea? Or flowers I'd cut and display in my kitchen? How significant is this risk, and is there any way to mitigate it?

Or should I just plan to have everything in containers and/or indoors for the rest of the time that I live here?

Any hard data as well as anecdotes are welcome. I've checked the top Google results and they're all pretty general.

posted by knotty knots to Home & Garden (14 answers total)

My leach field is in my back yard; I walk on it; dog plays there. Not a problem. You'll get some broken-down nutrients as a bonus.
posted by theora55 at 10:13 AM on April 5, 2023 [2 favorites]

Most are fairly deep into the ground, so I'd guess they mostly leach downwards vs upwards, and most garden plants don't root really deep. So if there was a concern, it'd be something that caused a leach upwards, like a flooding rain or a long passage of time.

They are bad for ground water, but for surface plants? you probably have some years.
posted by The_Vegetables at 10:18 AM on April 5, 2023 [1 favorite]

Response by poster: To clarify: my leach field is also in my backyard, and therefore I'm not planting anything there that I might want to eat (because my understanding is that the soil at root level contains human wastewater). I thought my front yard was a safe area, until I learned that a neighboring waste system abuts it.

But maybe for what it's worth: "my" portion is towards the end of the system's filtration line. So the bulk of the waste would have been filtered by the time it got to my side?
posted by knotty knots at 10:27 AM on April 5, 2023

I had a similar question with my property. This University of New Hampshire extension article advises against it for more than bacterial contamination issues.

https://extension.unh.edu/blog/2019/12/it-okay-plant-garden-over-leach-field

A good map of where the pipes are will help you make a decision, but your local ag extension at a university should be able to advise especially on the particulars of your areas soils.

I think flowers are a great option for this space, and I'm growing a lot of Mediterranean plants, including some herbs, but not for eating. I'm planning on putting in some bulbs for spring color.
posted by typetive at 10:45 AM on April 5, 2023 [2 favorites]

Your plants will be very, very happy with all the extra water and fertilizer. It’s the opposite of a problem.
posted by Melismata at 10:45 AM on April 5, 2023

Some thoughts from my experience with humanure. Humanure is not septic, so I don't know about root systems impacting septic fields and tanks.

- You can test your soil for fecal coliform!
- With humanure, out of an abundance of caution, it is recommended to use manure that has sat for a year. You can grow ornamental plants and fruit/nut trees and shrubs, but not a vegetable garden.

From a "can I handle this" perspective, I would expect you to be fine to cut flowers and display them in your kitchen.
posted by aniola at 10:47 AM on April 5, 2023 [1 favorite]

typetive, that link says you shouldn't plant over it because it can damage the leach field. It does not say you shouldn't grow next to it (except trees with long roots).

I'd be slightly wary growing tubers within a couple feet and I'd wash my hands after digging in the soil, but I'd grow and eat anything from there unless your neighbor is on some toxic drugs like chemotherapy, and even then I'd just give a couple feet of space.
posted by flimflam at 10:52 AM on April 5, 2023 [4 favorites]

If in doubt, why not make a raised bed, with a barrier layer at the bottom.
posted by Rhedyn at 10:54 AM on April 5, 2023 [13 favorites]

Yes I read the UNH extension page too. The better question here is "how sharp of a boundary is 'the edge of a leach field'?"

Obviously all contaminants don't magically disappear where the pipes end. You'd have to assume they go right up to the property line, and then add some number of feet to be sure you're clear of it. But gardening adjacent to a leach field is not the same as gardening over one.
posted by SaltySalticid at 10:56 AM on April 5, 2023

Would you consider a raised bed?
posted by chesty_a_arthur at 10:58 AM on April 5, 2023 [1 favorite]

Almost certainly you'd be ok to plant (and harvest) anything except deep-rooted/aggressive plants that might root into the pipes. But personally, and to be conservative, I'd want to know a couple of things. First, how deep are the drain pipes? Often they are around 3' deep, but can be much shallower. Second, how well do your soils percolate? If these are well-drained soils, then the effluent will go downwards easily. But if you have more impermeable soils (like clays, or shallow bedrock), then the effluent might go sideways since it can't easily go downwards.

Your neighbor might know the first answer, and either you'll already know the second from digging in your garden or you can easily find out via NRCS or the county.

As long as the soils are reasonably well-draining and the pipes are deeper than the root systems of what you are planting, I don't think you have any concern at all. But for an abundance of caution, you could avoid plants like potatoes and carrots where you harvest from underground, and maybe even avoid things like lettuce where the leaves get a lot of splash from the soil whenever it rains, and stick to plants like blueberries or Brussels sprouts where you are eating exclusively from out on the branches (i.e., letting the plant filter out anything that might be in the soil).
posted by Dip Flash at 12:40 PM on April 5, 2023 [2 favorites]

I would consider making a high raised bed. Not like a few inches high, but a few feet. I currently have my vegetables in 2 ft tall raised beds just because I have a chronically malfunctioning shoulder and having my plants up higher helps me to not hurt myself every time I go out and weed or prune things. This also gives me more control over the soil quality and moisture level for my plants. AND I'm not walking around with muddy knees all the time like I used to when I grew everything at or just above ground level. It's great. Do recommend.
posted by BlueJae at 12:52 PM on April 5, 2023 [1 favorite]

I would not hesitate to plant vegetables if it were more than 10' from the drain field to the plants. For cut flowers, right next to the drain field would be fine.
posted by ssg at 2:04 PM on April 5, 2023

This depends to some extent on what is actually being output - is it just a pure septic output or is it output from a waste treatment system?

You should not plant anything you intend to eat within 5m of your wastewater system. As the purpose of your system is to treat wastewater, the soil around your system contains bacteria which should not be consumed.

I doubt this is a pure septic system, so the above guideline should be followed. Raised beds may allow you to plant closer for vegetables, which don't usually have extensive or deep roots.
posted by dg at 4:17 PM on April 5, 2023