Can You Have a Raised Garden on Top of a Septic Field?

Confine gardens -- even raised beds -- to the perimeter of your septic drain field.


A sunny expanse of open lawn isn't prime real estate for a new flower or vegetable garden when it covers your home's septic drain field. Even though a septic system does its work out of sight underground, gardening on top of a septic field -- even in a raised bed -- risks your health and the function of your home's expensive waste-handling system

Septic Field Basics

Rural and suburban homes that don't have access to municipal sewer systems rely on individual septic systems to carry waste and waste water out through the plumbing system to decompose in and safely disburse into the soil. Most systems consist of an underground holding tank for solid waste that attaches to drainage lines set in gravel to aid drainage and filtration, and buried 6 to 18 inches underground. As water moves through the tank, the solids settle and the waste water flows into the drainage field, where soil microbes clean up harmful bacteria before it filters down to ground water. The 18- to 36-inch-wide lines can be up to 100 feet long and set 8 to 10 feet apart. How many your field includes and their length is based on the number of people in your household.

Plant Pros and Cons

Plants help your drain field function, by stabilizing topsoil to prevent erosion of the soil that covers it and by pulling out excess moisture. Plants that grow too deeply however, can damage the drain lines -- even perennials and some vegetables produce roots long enough to interfere with shallow septic fields. Increasing soil depth with a raised bed or mounded garden seems logical, but also impedes septic field function by decreasing the amount of oxygen -- needed to break down waste -- at the depth of the drainage field and by decreasing evaporation. Watering a raised bed planted with vegetables or other moisture-loving plants can stress the capacity of the drain field and other typical gardening tasks such as tilling and fertilizing can also compromise drainage fields. Plants that support drainage fields have shallow, mat-forming roots and need little water or maintenance.

Edible Concerns

When you plant vegetables and fruit over a septic field, you risk a harvest spiked with harmful bacteria. Root vegetables and low-growing leafy greens are most at risk for contamination with human pathogens, such as E. coli, which you could end up eating. Wash any garden vegetables thoroughly before eating them. Wear garden gloves to protect your hands from contaminants whenever you work in any type of planting over a septic field.

Plan Before You Plant

Learn exactly where your septic field is buried in your yard before you start planning a raised bed, or any garden or landscaping project. Septic system layouts are often included in home inspections or closing documents from the purchase of your home. Vegetable gardens and other raised beds should be at least 20 feet away from your septic field if possible, or at least on the end of the field farthest from the septic tank, because the far end of the drainage field often stays clear of discharge. Plants with deep roots, shrubs and trees should be planted 20 to 50 feet from the drainage field.

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