I would like to know if it is safe to grow a vegetable garden over a septic field; root vegetables, above-ground vegetables only etc. Any information very much appreciated.
Hi, It is totally and completely safe to grow anything you want over a septic field. As long as the system is functioning right then the only thing that should be coming out will be clean/safe water. If the area is soggy and/or smelly then you should worry more about the septic system itself than the vegetables you grow there. Lol One possible issue it planting trees or something that might grow into the septic system and mess up the structure. I don’t know how deep your system is, but it may also be a problem tilling and hurting the system. As far a germs or bacteria I don’t think you need to worry about a thing. Michael
We have put framed, raised bed veggie gardens on our septic mound- they do very well. I guess I would hesitate to grow root veggies right in the mound, but a 12" raised bed gets them above the effluent.
We were advised by the designer and builder of the one here, not to put top soil on the drain field, not to till it, but planting small shrubs and smaller plants would be fine. A master gardener told me that planting over the drain field is great: nitrogen is released from below contributing to healthy gorgeous roses, in that case. I rescued and planted a Quercus robur sapling in a hot, windy site in Idaho, where I did not think it would make it. Now that it looks great and is about five feet, I think that I should move it because it is so close to the septic tank itself. I have a friend near Escondido, CA, who described a thirsty oak once getting a rootlet into the septic system and totally clogging it up with the roots that thrived therein.
Laurie, I once took the Watershed Masters' course through extension, and the class focused on septic systems (specifically on system failures and their effect on local water quality). We had several experts speak to the class, and we talked extensively about planting on and around septic fields. We were told that you could put up to 18" of soil on top of the field, and broken flagstone paving was okay. We were advised to keep aggessive rooted plants farther away (willows), but most plants could be planted directly in the field. This was before pumped field were common; he mostly was addressing gravity fed fields. Maybe things have changed with the power fed designs.
Thanks, Terry. That is most welcome news, especially since the soil over the drain field, which was built on a slope here in 1987, is so compact that I have too much trouble with a shovel creating the smallest hole there. It seems that the builders said that they planted the drain pipes just 18 inches below the surface, but I know that some pipes are little over a shovel deep probably due to erosion. They even suggested not planting over the alternate drain field, but there is no way that that advice will be followed. I read your entry to suggest that there should be no problem with non-variegated Japanese maples. I would think that the cultivars sensitive to excess fertilization should be avoided, however. I need to check on whether the new tank to which I am referring in Idaho is pumped rather than gravity fed. Nevertheless, the oak is probably 15 feet from the tank. Would you advise moving it? I realize that it has a tap root, but it has only been there probably four years, and there is plenty of other space for it in the garden on the opposite side of the house. At times I even question a Salix matsudana 'Tortuosa', which has been growing rather slowly for probably five years approximately 25 to 30 feet from the tank.
Septic fields in BC are highly regulated and those regulations have changed over the years so that you may not be able to replace a failed field in it's current location, or may be required to do extensive and expensive upgrades. Field costs in our area are rarely less than $10K and up to $20K, more for an engineered system, so your priority should clearly be the septic, not the garden. Root incursions are probably the leading cause of obvious system problems (blockages and backup), while lack of maintenance (pumping mainly) the leading cause of field failure. Compaction and impervious soil coverings (clay soil) will also reduce the system functionality (aerobic requires air!) to the point where the runoff may not be as safe as we might wish. The preferred field covering is always a shallow rooted grass such as creeping red fescue. If your septic field is your only gardening option, I would suggest raised beds with a weed barrier cloth lining, at right angles to the field runs. Ralph
It surprises me, Laurie, that the soil is so compacted over your field- our raised field, which was installed in 1981, is mostly sand, and years of organic matter, and quite soft. It has never had anything but foot traffic- has yours been compacted by vehicles? I do agree with Ralph in that it is very important to maintain your septic system by regular pumping. Roots in the effluent pipes should not be a problem as long as they are not too agressive. I would avoid any tree that gets big. Where I grew up, east of the mountains in orchard county, the septic fields are often run down the rows of the orchards between the trees.
We are dealing with compact glacial till here, but I would think that the soil would be more pliable in the drainfield. With an average of 48 inches of rain on the slope, erosion may definitely be a factor. I need to look into this further because, apparently from my reading just now, there should be more than six inches between the surface of the soil and the drain pipes. I do plan to keep the access to the ports of the tank free of plants because we do regularly have the system pumped, and it is just easier. By using the keywords landscaping, septic, and system, I found some good articles. For local advice, e.g. do not plant root vegetables on the drainfield, see: "Landscaping Your Septic System" at www.wsg.washington.edu. The following quotation, however, is from http://www.extension.umn.edu/distribution/horticulture/DG6986: "Do not plant edible plants, such as vegetables and herbs on a mound or drainfield." Yes, grasses are the preferred plant for the drainfield, including ornamental grasses. However, I need to read further to find if they really mean grasses such as Miscanthus sinensis 'Gracillimus', which I doubt if the drain pipes are so shallowly planted at 18 inches, but most likely if they are at 30 inches.
Laurie, thought I'd post a picture of our septic field/ raised mound. The only shrubs planted directy in the field are 2 dwarf pines. The other shrubs are around the edges. The veggies are in the raised boxes, and the rest of the plant material is rock garden/alpine plants.
