Septic Tank Vegetable Gardens – Tips For Gardening Over Septic Tanks
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By: Susan Patterson, Master Gardener
Planting gardens on septic drain fields is a popular concern of many homeowners, especially when it comes to a vegetable garden over septic tank areas. Keep reading to learn more septic system gardening info and whether gardening over septic tanks is recommended.
Can a Garden be Planted Over a Septic Tank?
Gardening over septic tanks is not only permissible but also beneficial in some instances. Planting ornamental plants on septic drain fields provides oxygen exchange and helps with evaporation in the drain field area.
Plants also help control erosion. It is often recommended that leach fields be covered with meadow grass or turf grass, such as perennial rye. In addition, shallow-rooted ornamental grasses can look particularly nice.
Sometimes gardening over septic tanks is the only place that the homeowner has to do any gardening, or perhaps the septic field is in an extremely visible spot where landscaping is wanted. Either way, it is ok to plant on a septic bed as long as the plants that you use are not invasive or deep-rooted.
Best Plants for Septic Field Garden
The best plants for a septic field garden are herbaceous, shallow-rooted plants such as the grasses mentioned above and other perennials and annuals that will not damage or clog the septic pipes.
It’s more difficult to plant trees and shrubs over a septic field than shallow-rooted plants. It’s likely that tree or shrub roots will eventually cause damage to pipes. Small boxwoods and holly bushes are better suited than woody shrubs or large trees.
Vegetable Garden Over Septic Tank Areas
Septic tank vegetable gardens are not recommended. Although a properly functioning septic system should not cause any problems, it is very hard to tell when the system is working 100 percent efficiently.
Vegetable plant roots grow down in search of nutrients and water, and they can easily meet wastewater. Pathogens, such as viruses, can infect people eating the plants. If possible, it is always wise to reserve the area over and near the septic field for ornamental plants and plant your vegetable garden somewhere else.
Septic System Gardening Info
It is always best to gather as much information about your particular septic system before you plant anything. Talk to the home builder or whoever installed the septic system so that you understand what would work best for your particular situation.
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Planting Vegetables Over a Septic Leach Field
“Can I plant a vegetable garden on my septic tank leach field?” – Eric
The septic tank leach field is a tempting spot for a vegetable garden – it’s large, flat, and usually sunny. However, it is generally not recommended to plant vegetables in this area, for several reasons:
There is a risk of contamination:
- As septic tank effluent drains out into the lines, it is filtered slowly through the soil, and beneficial soil microbes digest harmful bacteria and viruses. That means that near the lines, there is some amount of contamination, and the extent depends on the type of soil, the rate of absorption, and the quality of the system. While septic systems are designed to prevent disease-causing soil contamination, there’s no easy way to know if your system is functioning properly.
Also, the proper functioning of your septic system can be harmed by:
- Raised beds that interfere with the evaporation of moisture.
- Tilling, digging, and foot traffic, which can damage the septic lines.
- Irrigation, which upsets the careful process of filtering and evaporation.
Instead of vegetables, plant your septic leach field with shallow-rooted, drought-tolerant ornamental plants, grasses, or ground covers. For more information, and plant suggestions check out:
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I have cucumbers planted close to my drain field but not over it. And the slope is such that surface water over the drain field would run away from the plants. So I am not too worried about them. But absolutely its not a good idea to plant veggies over the septic tank drain field.
I am wondering how close to a mound septic system I can plant my vegetable garden, and still be safe from harmful contaminants. Would 10 feet from the base of the mound be sufficient distance?
I have planted a garden on my mound system for years I also added at least a 6′ layer of organic dirt from an dairy and cattle farm nearby. I have never had any problems and harvest huge amounts of vegetables…if you do not use harmful chems in your house hold they will not be in you septic system and not contaminating your food. the garder covers the entire system top sides and below.
I have a 20 by 50 foot garden which is sitting over a septic drain field…I added 6 inches of black dirt and get amazing vegetables…..I have never once had an issue….
The drain tubes are 30 inches down and my only worry would be the roots of some plants…..but as far as contamination…never…..plant on…!
I have one of these $25,000 alternative engineered septic systems where the leach fields are only 12 inches down. Supposedly the water comes out clear. Do you think it is safe to grow vegetables in this shallow dirt?
My husband has been digging up tree roots along the edge of our septic mound. He was going to put it out in the pasture where new born kids will be. Is this dangerous to the goats, land, and wildlife?
I see a lot of information about planting on or near leach fields. How long after a leach field is done being used can I plant vegetables safely? Does the leach field have to be dug up? Thanks.
my lines are 30″ in the ground and I have a wonderful garden year in and year out.
I was going to put raised beds 10 inches above septic bed 12 ft by 6 ft ( 2 beds ) If I put that black cloth down so roots don’t go any further will the beds harm septic system??
are rhubarb roots to deep to plant over drainfield?
I was thinking about doing a 20×20 carving pumpkin patch over the septic leach field. Would this be safe as it is not intended for consumption?
Is It Safe to Plant a Garden Over a Septic Field?
You might think it’s a great idea to plant a garden over your septic field. However, it really is not the best place for a vegetable garden. Certain shallow-rooting plants can help the septic drain system work better by eliminating dampness and nutrients from the soil. They can also decrease soil corrosion.
Saviour Septic, LLC advises using your septic field for decorative plants instead. Having said that, if you do not have any other spot for your vegetable garden, we recommend taking the following precautions:
- Be sure to not plant root crops over any drain lines.
- Lettuce and other leafy vegetables could possibly get tainted by splashing rain, which throws soil onto the plant. Therefore, you may want to mulch them to reduce splashing, or not grow them at all.
- Fruit is a little safer. Make sure you put those that grow on vines, like cucumbers or tomatoes, onto some sort of support so that your fruit is off the ground.
- Carefully wash produce from the garden prior to eating.
- It is never a good idea to build raised beds over your field. They could constrain evaporation of moisture.
- Lilies have shallow roots and are a beautiful plant to put over the septic field.
Again, we would recommend planting shallow-rooted plants that are not extremely water-loving on septic fields. The pipes in your leach field are usually approximately six inches below the ground. These pipes permit septic tank waste to drain over a hefty area. As it seeps into the ground, the waste is rinsed by the soil. Plant roots can aid in removing extra moisture and nutrients, making the sanitization of the residual waste more effective. However, roots that block or disturb pipes can harm the drainage field.
Image credit: A creative way to deal with a septic tank! (http://outlawgarden.blogspot.com)
Bottom line – Leach field gardening can be a challenge, but if you shop around, you can find plants that will fulfill your landscaping needs, while not interfering with or blocking drain pipes. Go for the flowering perennials and annuals, turf grass, and other ground covers, which are not likely to damage the lines. In addition, do not over till the soil and make sure you wear gardening gloves to protect yourself from contact with any unsafe organisms that could be present in the soil.
Maintaining septic drain field vegetation
As much as you may want to plant over the drain field so that it blends seamlessly with your garden and lets you forget its existence, this is not the best idea.
Keep your drain field visible, or make people aware through other means, like a plant barrier or fence. Don’t hold large social gatherings, mowing the lawn is just fine, but certainly, limit the foot traffic.
Always ask your Septic System Installer if you are unsure of any possible situations that can negatively affect your system.
But don’t be alarmed if any of these trees are already growing on your property. This is fine, so long as they are at least 50 feet away from your septic system and drain field.
Trees that can be safely planted closer to the drain field include ornamental trees like dogwood, cherry and crabapple, hemlock of the red, scarlet and white oak varieties, and small pines such as Mugo pines. Keep these trees as far away from the septic tank and drain field as the mature height of the tree, or at least 20 feet.
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According to U.S. Census Bureau data, Maine is the most rural U.S. state, with roughly 61 percent of our population residing in rural areas. 1 Because many rural-area homes are not connected to municipal sewer systems, many Mainers rely instead on septic systems to discharge home wastewater.
Planning Around Your Septic System
A septic system consists of an underground tank and a soil absorption field, also known as a septic system disposal field, and sometimes called a “leach field.” The disposal field cleans the wastewater through filtration and the action of microorganisms in the soil, preventing polluted water from entering lakes, streams, and groundwater.
The existence of a septic system on your property means that you may have to plan your land use around it. Driveways, play areas, sheds, patios, and gardens must all be designed with your septic system in mind. This particularly applies to vegetable gardens. In fact, the Maine Department of Agriculture explicitly advises homeowners to avoid locating vegetable gardens on or near septic system disposal fields.
What if You Don’t Know Where Your Septic System Is?
Locating your system is not always an easy task. Even if you find your septic tank, the disposal field can be many feet away.
To locate your system, refer to your septic system design form (known as the HHE-200 form). If you can’t find a copy, contact your local plumbing inspector to see whether he or she has a copy on record. You can also contact the Maine Subsurface Wastewater Program through their Maine Subsurface Wastewater Team page on the Division of Environmental and Community Health (Maine.gov) website, 1 or by calling 207.287.5689. This program receives and holds all septic system records from towns since 1974 (the newer the system, the more likely it is that they will be able to find the record). If no record can be found, you can contact a Site Evaluator to locate your system.
How Septic System Wastewater Can Contaminate Your Garden
Untreated wastewater, also known as sewage, can be a health hazard. Septic system disposal fields are designed to treat, or renovate, this wastewater. The most important reason you should not install a vegetable garden on top of, or right next to, a septic system disposal field is because the plants can become contaminated by wastewater that has not yet been renovated by the field. Plants on disposal fields can absorb wastewater pathogens. Eating vegetables that have absorbed wastewater pathogens can make you very sick.
What You Should Know About Disposal — Field Design
Most septic system disposal fields designed since 1974 are installed either partly or completely above the original ground surface. This is because most of our soils in Maine have hardpan, bedrock, and/or a shallow seasonal groundwater table. The bottom of the disposal field must be elevated above any of these limiting factors in order for the wastewater to drain into the soil and be renovated.
How a disposal field is constructed
The main body of the disposal field — the lowest layer — consists of components such as plastic or concrete chambers, fabric-wrapped pipe, geo-textile sand filters, or stone. The purpose of these components is to provide storage capacity for the wastewater, which is usually generated in spurts, faster than the soil can absorb it: people usually generate the most wastewater in the morning before work and school, and in the evening after coming home.
Just above the stone or other disposal-field components is a layer of compressed hay or filter fabric, which prevents fine soil particles from entering spaces among the stones or in other devices. If the spaces in the stone or other components become filled with soil, they will not be able to store wastewater, and the septic system will fail.
Above the compressed hay or filter fabric is a layer of fill material, usually eight to twelve inches deep. The lower part of this fill is supposed to be a gravelly, coarse sand material. This is to allow for the free exchange of air into the disposal field so that microbes can quickly attack and renovate the wastewater. Generally, only the top four or so inches of this fill material has silt or clay and organic matter in it.
Why septic system disposal fields are unsuitable garden sites
- In a brand-new septic system disposal field, the wastewater level in the disposal field is usually quite low. Over time, however, as the disposal field matures, ponding of wastewater can be expected. This results from the partial clogging of the soil pores by particles escaping from the septic tank, and the living and dead bodies of microorganisms. The thicker this clogging layer gets, the higher the wastewater level in the disposal field becomes. The wastewater level will also rise over time as family members increase and grow up, and as a result of heavy-use events. Eventually, the wastewater in a disposal field will very likely reach high enough levels for even shallowly rooted plants to come in contact with it.
- Water (including wastewater) will wick up into soil due to capillary attraction. If wastewater rises high enough in the disposal field to come in contact with the fill material on top of it, capillary attraction could cause the wastewater to wick up to as high as 18 inches, depending on the texture of the fill. This is why a vegetable garden should not be placed on a disposal field fill extension, especially near the disposal field. Even though there may be no wicking up to the top of the disposal field or fill extension material at first, it may occur as the disposal field matures.
- Generally, the soil over the top of a septic system disposal field is very permeable, particularly soon after the disposal field is installed. Therefore a garden planted on top of a septic system disposal field would require watering in order for the plants to prosper. The problem is that adding water to the top of a disposal field, particularly if the disposal field is only marginally functional, could cause it to fail.
- Rototilling the top of a disposal field can damage the compressed hay or filter fabric. If the compressed hay or filter fabric is damaged, it could allow soil particles to migrate down into the stone or other devices in the disposal field, reducing the wastewater holding capacity.
- Placing additional fill over the top of a disposal field, in order to create a safe zone for vegetable plants to grow, is not a good idea. The additional fill material might suffocate the disposal field by inhibiting the free exchange of air. An anaerobic (oxygen-free) disposal field is much more likely to clog up and fail than a well-oxygenated one. In addition, placing additional fill material on the disposal system could result in damage to disposal field components.
- Any plants installed on the top of the disposal field will send roots down in search of water and nutrients, neither of which will be found in the gravelly sand fill material. Ultimately, septic system disposal fields make unsuitable garden sites because roots that come in contact with wastewater can take up pathogens, such as viruses, which can then infect anyone who eats the plants.
Better Choices for Covering Disposal Fields
The most suitable vegetation to grow on top of septic system disposal fields and fill extensions is grass. Flowers may also work, but only if you avoid rototilling the soil and watering the plants. Woody-rooted plants should not be planted on disposal fields or fill extensions, because the roots might clog up pipes and other devices in the disposal field. If you do not want vegetation to grow over your disposal field, covering the bare soil with bark mulch is an acceptable solution.
Adapted with permission from:
David Rocque, Maine Department of Agriculture Policy on Establishment of Vegetable Gardens on Septic System Disposal Fields (Augusta: Maine Department of Agriculture, Conservation and Forestry, 2012).
John M. Jemison, Jr., Your Septic System, Bulletin #7080 (Orono: University of Maine Cooperative Extension, 2002, 2010).
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Answer #1 · Gardenality.com's Answer · Hi Laura! - Most septic field lines are buried 6 feet or more deep. Even so, many plants and trees planted too close to septic field lines will find the water source and eventually invade it. This can cause major problems. But there are some shrubs and trees you can plant without much worry. Herbaceous perennial and annual plants shouldn't be a problem at all.
In general, it's best to choose shrubs and trees that have shallow root systems, such as azaleas, holly, boxwood, Japanese maple, crape myrtle and dogwood which are all fairly safe. Avoid fast-growing plants or those that are known to like a lot of water such as river birch, weeping willow, red maple, ligustrum and privet. As a general rule, I would suggest keeping any shrubs or trees at a distance of at least twice their total mature width from the septic lines. That would mean a plant that grows to 6 feet wide at maturity should be planted at least 12 feet away from the septic lines. It's always better to be safe than sorry.
Regarding how to prepare the area for planting. The septic lines are deep enough that you shouldn't have to worry about hitting them when digging or tilling. Too, you shouldn't be planting shrubs or trees right over the top of the lines. So, I would just use the same method you always use when planting. I rarely till a bed. Instead, I just dig the planting hole three times as wide as the container the plant was growing in and, usually, no deeper than the root ball.
If you bring a picture of the area to our nursery we can give you some suggestions as to what to plant in the area.
Let me know if you need any more details or have any other questions.