When gardening season is in the planning stage, homeowners that rely on a septic system will begin looking around their yards, wondering whether they can plant a garden over their septic drainfield. Leach fields were designed to be covered with vegetation, so are not good places to put just plain gravel, a patio, or other inert products. Plants help the leaching system operate correctly by removing excessive moisture and minerals from the soil and reducing erosion.
But unfortunately, as tempting as it may be, gardening over your septic drainfield is not a good idea. In fact, septic owners need to be pretty careful about what they plant over the drainfield, gardening aside. When you do plant over a leach field, plant densely, because the soil should be well covered with vegetation.
Read on to discover the reasons gardening over a drainfield is not recommended and to discover what can and can’t be planted safely instead.
What is a Leach Field?
A leach field is one of the major components that make up a septic system. Located underground, it is a network of small, corrugated pipes that are connected to the septic tank via the outlet pipe and a distribution box that handles the pressure distribution by allocating wastewater into several absorption trenches in the yard.
Also called a drain field, the main job of the drain field is to remove contaminants like harmful coliform bacteria from septic tank effluent via perforated pipes or corrugated drainage pipe called leach lines that soaks the surrounding soil. Using the soil bacteria to naturally remove nasties before they reach the water table or groundwater.
How a Septic Drain Field Functions
Understanding how a septic system functions is essential to making sound decisions about how to best landscape over the drain field. A standard septic tank will separate solids from liquids. The liquid effluent, or wastewater, will then flow from the tank into a series of drain lines that allow the effluent to slowly percolate down through the soil in the drain field. Many different soil microbes will act to filter and cleanse the liquid effluent before the harmful bacteria in it has a chance to reach ground water. These soil microbes require oxygen to function optimally and perform less effectively in compacted and/or saturated soils. This is why it is recommended to keep excessive traffic off the drain field to avoid over-compaction of the soils.
It is also recommended to keep excessive moisture from flowing over the drain field. This can be accomplished by diverting runoff from a roof or driveway away from the drain field and making sure that irrigation systems do not add excessive moisture. It is recommended that sprinkler heads be positioned so that no irrigation water comes within 10 feet of the drain field.
Gardening Over the Drainfield
We understand the appeal of transforming the lawn above your drainfield into a lush garden, but unfortunately, growing food over the drainfield is a dangerous idea. While a properly functioning septic system will not necessarily contaminate the crops grown above the drainfield, there is no way to guarantee your garden will not be contaminated. Unfortunately, even properly maintained septic systems do not always show problems before the problems get bad. If a part of your system has malfunctioned, you will not likely notice until wastewater is backing up into your house or the drainfield is saturated with effluent. This could result in a contaminated garden that you are not even aware of.
Also keep in mind that crops grown above your drainfield may also be exposed to household chemicals that are still present in effluent before it filters through the drainfield. Many of these are not safe for your septic system, let alone safe for human consumption.
The septic system drainfield typically contains pipes buried from 12 inches to 36 inches (depending on your system) below the ground. This does not leave much room for root growth. As a result, we recommend that you choose non-invasive perennials with shallow root systems. Most perennials have a root system that grows in a mat formation (surface roots) that is likely to remain above the drainfield. Woody ornamentals, shrubs, and trees usually have a taproot that extend deeper into the ground. Secondary roots grow laterally from the taproot and greatly increase the chance of growing into the drainfield pipes. This can cause the system to fail.
Vegetables on a Leach Field
Vegetable gardening over a leach field is a bad idea. Though properly functioning septic systems won’t contaminate the soil with harmful pathogens, there is no easy way to guarantee that the crops grown over a leach field will be safe to eat. Furthermore, vegetable gardeners may not be keen on growing their food plants in soil that is frequently inundated with household chemicals. Unfortunately, placing raised beds over the drainage area isn’t a good solution either. The added soil depth of the beds may inhibit evaporation and limit the effectiveness of the septic system.
Before planting, it is a good idea to check the soil pH. The detergents and cleaning products that go down the drain are usually alkaline and may elevate the soil pH over time. Depending on what you want to grow, you may need to amend the soil to adjust the pH. Moreover, household effluent generally contains high levels of salt, especially if you have a water softener. Plants that can tolerate salt exposure are more likely to thrive.
Trees and Shrubs
Ideally, you should avoid cultivating trees and shrubs not only over a septic field, but even nearby. If you don’t have a choice, prefer small shrubs because their roots are usually not as long and are unlikely to infiltrate underground pipes and drainage areas.
Plant any tree or large shrub no closer than about 20 feet from the leach field. Trees reputed for their invasive roots, like willows, poplars, elms, and silver maples, should be planted even further away: 50 feet. You can however plant a tree near a leach field as long as you take the precaution of installing a rhizome barrier (bamboo barrier) in the soil between the field and the tree.
Groundwater Contamination Effects
With all the chemicals seeping and leaking into the groundwater supply, scientists warn about the dangers of contamination.
- Health Risks
Health effects are some of the greatest risks associated with groundwater pollution, as it easily penetrates the food chain. These risks and damages include poisoning (of animals and people), dysentery, or hepatitis. The more contaminated the water supply is, the more dangerous the consumption of polluted water becomes for humans, wildlife, and even farm animals.
- Economic Risks
When the groundwater is contaminated, the problems aggravate in a cascading manner, affecting the economy. This means that vast areas of land depreciate, while many industries relying on underground water sources become vulnerable.
- Environmental Risks
Last but not least, the environment is the one suffering the most because of groundwater contamination. Toxic water present in ecosystems can lead to devastating effects, damaging habitats entirely. Moreover, nutrient pollution can lead to severe consequences of the entire environmental chain.
What Can You Plant Over the Drainfield?
Shallow-rooted plants, like perennials and some grasses, remove excess moisture and nutrients from the soil (especially phosphate and nitrate, both of which are commonly found in effluent and which contribute to algae growth in freshwater bodies). Their shallow roots also hold the soil in place during heavy rains, which helps guard against erosion. Turf grasses are the standard choice. Be careful not to plant tall grasses above your drainfield, as these have exceptionally deep and invasive roots. Perennials, annuals, and groundcover can safely be planted above your drainfield.
Follow These Landscaping Do’s and Don’ts
(U.S. Environmental Protection Agency)
- Plant grass or keep existing native vegetation. These are the best covers for your drainfield.
- Direct all surface drainage away from the septic system
- Use shallow-rooted plants. Tree and shrub roots can grow into the drainlines, clogging and breaking them.
- Avoid water-loving plants and trees
- Make sure the tank lid is secure
- Plant a vegetable garden on or near the drainfield
- Put plastic sheets, bark, gravel or other fill over the drainfield
- Reshape or fill the ground surface over the drainfield and reserve area. However, just adding topsoil is generally OK if it isn’t more than a couple of inches
- Make ponds on or near the septic system and the reserve area
Keeping Your Septic Tank Healthy
To keep your septic tank healthy, you need to keep the “good” bacteria in it. Harsh detergents, bleach, and chemical drain cleaners kill the good bacteria in your septic tank. One way to add good bacteria to your septic system is to flush a packet of brewer’s dry yeast down one toilet on the bottom floor of your home one time per month. Try using biodegradable and “septic safe” cleaning products such as vinegar and baking soda.
At West Coast Sanitation, we know that you do not have time to deal with septic problems. One of the ways you can maintain this balance and keep your septic system working like it should is to have your tank pumped regularly. Please give us a call at (951) 780-5922 right away. We have professionals ready to answer your questions and get your system working properly again.