Can I put raised beds over a septic leach field

Tom4271(6a and 7b)April 28, 2012

I've got a front yard that is sandy and has good drainage (on Cape Cod, Mass). The septic system leaching field is underneath it. It has fantastic south exposure. So I'm thinking about putting raised vegetable beds on it - not covering the whole area but 3 4 by 10 foot beds. Many seem to think this is a bad idea.

Based on my searching, I've heard the following:

- Raised beds can impair the function of the leaching field (the pipes a several feet below) - I have no idea why except maybe because you water the garden and that may be a problem or perhaps the weight of the beds. ??

- All kinds of irrational fears about the effluent being sucked up by the vegetable roots. This makes no sense since water goes down not up and even the deepest vegetable roots are only 2-3 feet deep at the deepest. Even then some nitrogen rich water would seem to me to be a bonus.

I'm interested in experiences anyone has had with this sort of situation. What's really the bottom line here?

Thanks for any help-


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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

What's the bottom line? That the choice is yours. While it certainly isn't recommended, if you are comfortable with it go for it. It is your leach field and your garden.

Just keep in mind

(1) that water doesn't go straight down, it diffuses out first and

(2) during periods of heavy rain, run-off, or snow melt water can actually go up, rise in the soil

(3) while N found in the effluent may be beneficial for the plants to a degree, excess N also poses problems for plants and all the bacteria in it may not be quite so "beneficial" :)

(4) and soil over leach fields tends to settle over time and that allows roots access to it causing possible plugging of the field as well as contamination of any foods grown there.

As one of the articles linked below points out, the leach field is the most expensive and the most potentially problematic parts of your entire septic system. So it can be money out of your pocket to mess with a good working one.

We live on one of the largest man-made lakes in the country with miles and miles of uninhabited shoreline yet the lake is still having some problems with septic contamination. I say this only to point out that even with thousands of acres of land involved and massive water dilution, bacterial contamination is still possible so it can't be treated lightly by the average home gardener. I have 8" raised flower beds planted over my leach field and because of the slope I wouldn't consider growing edibles there. If it were level I'd want at least 18" deep raised beds. JMO


University of Nevada AG Extension - Planting on Septic Leach Fields

Virginia Tech Extension - Planting on Your Septic Drain Field

    Bookmark   April 28, 2012 at 10:03PM
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I manage that area of my landscape for mulch production -- grasses and clovers I can mow as needed for vegetable garden mulch. Best use I've found for that space, and grass seed is kind of fun to play with.

On the other hand,I don't think veggies with shallow roots would tap the septic field because of the depth of the lines. However, disturbing the soil at the surface repeatedly could have some repercussions down below in sandy soil.

    Bookmark   April 29, 2012 at 8:58AM
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septic fields are so expensive why risk it? And if/when you have to have it all dug up...there goes your garden

    Bookmark   April 29, 2012 at 1:49PM
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I just had the septic pump guy here this morning. He said if I plant over the leach field, that's better for him because he'll have to come out more often to do maintenance on my field :)

A couple of things to add and echo from above:
Your veggies will be not only sucking up nitrogen from the leach field, but also all the cleaning fluids you've run down your sink, laundry, etc..

All leach fields have to be replaced at some time or another, and then you'll have to dig up your whole beautiful garden with soil you've worked for years to improve.

My guy was able to show me exactly where the lines and the field were with a probe he stuck into the ground (when he hit gravel or a line, it clunked). If you can get the parameters of the actual lines, you may find that you've got some areas in the southern exposure that do not interfere with the lines.
What about the other side of the yard?

And yeah, any roots in your lines are going to hasten the time when you have to dig up the whole thing. Maybe your beds would be too high to bother the lines, but the soil in raised beds definitely settles over time, and so you'd have a lot of work keeping the soil levels up from year to year, and that would mess with any year round harvesting you want to do.

I'd find out exactly where your field is, and put the beds someplace where they'll be safe if/when the field needs maintenance.

    Bookmark   April 29, 2012 at 2:51PM
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gardenlen(s/e qld aust)

g'dat tom,

this question pops up from time to time and it has those who oppose it and those that support it, for me as we now have a septic system i would have no issue spreading some mushroom compost or the like over the top of the leach pipes, this so i don't dig at all, and plant annual seasonal above ground vege' type plants ie.,. tomatoes, bock-choi/cabbages etc.,. that sort of thing, no root type crops(that involves digging though our way with our instant potato growing might be ok dunno? no digging involved).

laying something like mushy compost will stop any splash occurring though again your field would already need to be over saturated for that to occur, and would use mulch hay as well.

don't see that annual seasonal crop roots can cause any long term issues as they are seasonal plants and once expended their roots will rot away.

also plan on having our citrus and other fruit trees about 5 meters below the leach field, so any over flow goes to good use, below that we will have a habitat garden of native trees and shrubs. why let the grass enjoy all that nutrient?

so long as common sense prevails, science will only ever support those in control, so no good relying on scientific theory. again good old common sense.

gotta get real in times of drought there is all that water just down there.

so what is grown like from any garden gets washed after harvest and gets cooked. know people who pump out of their tank to gardens smell a bit but they are still very much alive and walking around.


Here is a link that might be useful: lens garden page

    Bookmark   April 29, 2012 at 3:06PM
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"science will only ever support those in control, so no good relying on scientific theory"

There's a few thousand years of what's now called "common sense" gleaned from this "science."

There's also plenty of dead gardens out there by people who want to conquer nature rather than letting the mistakes of the past guide them to a conclusion.

Besides, the only conspiracy scientists could cook up for this benefits those that sell/repair septic tank systems.

A lot depends on soil texture, soil moisture content, how much humidity is in the air, how much shade is on the septic lot, and how quickly it clears.

There's some areas where you can get away with planting on your septic field and many areas where you can do that and get a wonderful smell of fermenting bathroom.

The septic system in most areas are designed to take up "just enough" space in the landscape to do it's work and put up with the occasional heavy rain that doesn't dry out quickly...and little else. Some people may have a few acres with a huge septic field that gets full sun and even after the largest rain it's only "soggy" for a few hours while the sun bakes it out.

Generally you don't want a few hundred pounds of soil + constant moisture feeding plants hanging over your septic field. If you can get away without adding additional moisture you're already pushing your field if there's that enough available moisture that close to the surface of the field.

There's also the contamination thing, but that's so minor once you wash your produce. The real issue is growing a $2000 tomato because of what you've done to your septic field if it can't handle the extra weight/moisture and root displacement moving soil in the field.

    Bookmark   April 29, 2012 at 4:19PM
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I am reading this all with great interest as I just had a whole new system put in last year. I asked the man in charge about planting over it and he said I didn't have to worry about it at all.

The raised beds that I have for my veggies now, (and I am planning on adding similar ones over part of the drainage area) are about 18" high, though the soil is only about 12".

I have never seen water collect in this part of the yard, even after days of heavy rain. However I am going to re-think what I plant in those beds.

    Bookmark   April 29, 2012 at 4:54PM
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It all depends on the field.

"A lot depends on soil texture, soil moisture content, how much humidity is in the air, how much shade is on the septic lot, and how quickly it clears."

If you have 2 people using a septic field designed for a family of 5-6 then you have some leeway. If you have 5 people using that same field and it's in partial shade most of the day in an area where you get 30"+ of rain a might want to think about that garden location.

The age and design of the field also plays a's health compared to it's design.

There is no absolute yes/no on the issue, but for the most part it's a "no" for most people out there, a "proceed with caution" for some, and "no problem" for others.

    Bookmark   April 29, 2012 at 5:14PM
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Tom4271(6a and 7b)

Thank you all for the input. The leach field was installed last year. It's full sun all day. The drainage here has been historically very good. I had to move the field to this side of my house. But it's a perfect site for garden plots.

Sounds that most of you would not do it. I respect your opinions. I may research it a bit more but will likely not plant beds over the field.

    Bookmark   April 29, 2012 at 9:17PM
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In case you end up doing it, herbaceous plants (as all veggies are) are generally recommended for planting over a septic field. Woody plants are uniformly considered bad. There is virtually no bush or tree that will not try to get into the pipes.

Second, there is a product, copper sulfate I think, that you can flush down the toilet once a year during the growing season, It will kill whatever root is in the pipes on contact. It will affect your veggies nutrient balance some, since

Many veggies go down to 4 feet-6 feet, given a loose enough soil. Beets go to 6 with their tap root, tomatoes go to 4.
There is no time over a season to block a pipe, but hair roots will get in there and you should avoid perennial veggies (such as asparagus), or even perennializing something like, e.g., cardoon. True, most veggie roots will be in the first foot or so, and planting over septic fields has been done for centuries, so you will have to estimate health risks on your own.

Consider also which vegetables are eaten raw and which ones cooked. Most root crops here end up either roasted or in soup, for example. Either way, sterilization is certain. Same for winter squash, shelling peas, shelling beans. Lettuce, I would think twice, since it has hollow stems, OTOH its roots are so puny it is unlikely that it will get down to the pipes. Radicchio is eaten raw and has a tremendous tap root, so beware.

The lowest risk for the field is for plants that are planted near the end of the field, where water is scarce, the highest is for plantings near the top of the field, where water is abundant.

    Bookmark   April 29, 2012 at 10:53PM
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I gardened for many years with the edge of my cornfield overlapping the edge of the septic field. I had the soil tested multiple times and spoke with the county health department. I even checked for heavy metals, etc. Never had an issue and the veggies grew well. About 10 years ago, we moved the septic field but continue to grow over the edge of the old field - I know where it was because if I get near it I find the old fill rocks.

I do use raised beds which are at least 18" - 2' raised above the original soil level.

    Bookmark   April 29, 2012 at 10:53PM
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