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• Gardening over or near septic system components
• Advice for planting over or near septic systems

This chapter discusses the types of gardens or other plants that should or should not be planted over or near septic fields or other septic system components. This is a guide for homeowners who are planting trees, shrubs, gardens, ground cover, or other plants near a septic system and who need to know that can be planted near or over septic system components like the septic tank, distribution box, and drain field or soil absorption system. Planting the wrong things or in the wrong places can lead to the need for expensive septic system repairs.

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Planting Fruit, Vegetable, or Ornamental Gardens Near or Over Septic Systems

The short answer is it's better to keep fruits and vegetables away from septic systems, especially septic drainfields. Planting a fruit or vegetable garden over or near septic system components raises some important questions: Will there be pathogenic or chemical contamination of the soil (bacteria, viruses, cleaners) below the garden? Will septic system pathogens enter in or contaminate fruits or vegetables planted over or near the septic system? Will chemicals or salts passing through the septic system harm nearby plants? Will the garden planting itself harm the septic system in some way? The effectiveness with which the soil biomat is treating pathogens in septic effluent, the ability of the soil to filter effluent, the chemicals or salts entering the septic system, and the type of plants placed over or near the system are some of the factors that lead to answers to these questions. [The photograph above shows our vegetable garden gone wild in Costa Rica.]

• Septic effluent contains chemicals and pathogens which are potentially unhealthy or harmful to people, animals, or plants. If a septic absorption system's biomat is functioning successfully, the level of these pathogens is reduced to that of typical surrounding surface water before effluent leaves the drainfield. The "safe" distances involved depend on the soil type.
• Soil types affect how the septic system behaves and how it affects nearby plants of any kind. Clay soils release cleared effluent in perhaps a few inches but then clay doesn't perc well and is bad in general for a septic location. Sandy soils permit much greater travel of effluent and pathogens, certainly several feet. These "close" distances do not even consider what happens when the drainfield is not working well or is in failure. In that case pathogens may be released to the general environment and might travel any distance from the septic field.
• Root crops such as carrots or potatos which develop in the soil are likely to pick up pathogens from effluen in the soil over, next to, or downhill from drainfield trenches or galleys.
• Leafy crops such as lettuce or perhaps broccoli which develop above the ground but close to it may be contaminated by pathogens that splash up from the soil surface during watering or during rainfall.
• Above ground crops that grow on a raised vine such as cucumbers, tomatoes, or peppers may fare better if they must be planted over or close to septic system components, since they are higher up and less likely to be contaminated by soil splash-up.
• Salts and the septic system: Homes whose water supply is "hard" and which employ a salt-based water softener system are more likely to be passing high levels of salt into the septic drainfield. Not only does this salt risk harming the drainfield operation (mineral clogging or damage to the biomat) but such salts may also damage some plants that grow nearby.
• Chemicals and the septic system: At this website we've advised strongly against use of "magic bullet" chemical or other septic treatments as some of them are toxic and environmental contaminants. Some of these may also contaminate your garden.
• Gardening activities such as walking or digging into the first few inches of soil over a drainfield are not likely to damage it. But driving equipment such as a plow or rototiller over a drainfield or constructing a "raised bed" garden which requires the addition of soil above surrounding ground levels can damage the system or can reduce soil transpiration thus preventing the drainfield from functioning properly. Not "functioning properly" here means that the drainfield stops successfully treating the pathogens that flow into it. It stops working and begins discharging unsanitary effluent into the environment, and into your garden.

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More Information on Building Diagnostic Inspections and Repairs

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

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