Why is My Grass Turning Yellow Over My Drain Field?

If your home isn’t connected to a sewer system, chances are you have a septic tank next to your house somewhere in the yard. When things are working well, you won’t notice it’s there.

When something’s going wrong, however, it might become visible in the condition of your grass. Yellow grass, or dead grass, directly over the tank or pipes are signs that an inspection may be needed. If not a septic leak, it may be a sign of dry or too shallow soil.

The Septic Tank In Your Ground

There are various types of septic tanks, and yours will likely be specific to its location’s landscape and municipal regulations. The basic design is a buried tank connected to a building’s plumbing that filters and partially treats domestic wastewater.

In the tank, solid waste separates from water and is broken down by bacteria. The cleaner water towards the top moves out of the tank through a system of pipes outside of the tank, which can be up to 100 feet in total length. In those pipes, water is further cleansed by bacteria and then leached out into the surrounding soil.

The ground that contains this piping system is known as a leach field, or septic field, where the water runs through a layer of gravel in the surrounding soil as it moves downwards in the ground, sometimes rejoining a groundwater source. As the water moves downward, the soil filters it to a usable purity.

The Tank and Your Grass

Depending on where and when your septic tank was installed, it may be deeper or more shallow in the ground. Grass roots usually need at least 6 inches of clearance, so systems should be buried at least this deep but can be up to several feet under the surface.

Septic tanks can have lifetimes between 15 and 30 years and ideally should have an evaluation every year to be sure it’s functioning correctly. When there is a blockage or a leak, it can negatively affect your usually lush green grass.

Is Septic Water Good For Grass?

Septic Tank

In normal circumstances, the water that seeps into the surrounding grass should be fine for it since the bacteria in the septic system cleans the water enough to be safe for the soil.

When the water is being safely processed, the area will receive a regular source of moisture for the soil and any plants above it. That isn’t to say the grass should be greener over the drain field by default, especially if the tank is buried several feet below the grass roots. The leach field shouldn’t be left out of regular lawn watering.

Is Lawn Fertilizer Safe For Septic Systems?

Septic tanks are made to be water-tight, so fertilizers shouldn’t leach into the septic system to interfere with the filtering process. Most lawn fertilizers are designed to be held by the soil and absorbed by the grass roots, so the fertilizer shouldn’t be free to run through the soil and may not even reach the septic tank or piping.

Septic Tank Failure

If something is wrong with your septic tank, you may notice it in slower drains, odors from the area, or standing water over the tank. The condition of your grass is another sign there might be an issue worth looking at.

Noticing Yellowing or Dying Grass

The septic tank is next to the house, not under it, usually in a flat, open area. If you notice lines of yellow grass, these are outlines of the piping system below.

It may not necessarily be a problem when this occurs in the late summer during a dry period. The roots may be drawing in too much of the released effluent since the soil over the pipes and tank isn’t as deep as the other surrounding soil, which can store more water.

It may be, though, that there is a leak. If you see yellowing patches in the piping area when there is normal moisture, there might be wear or a crack in the piping.

Grass dying in the leach field, or a large patch of yellowed grass over the tank and/or piping area, is symptomatic of a larger problem. This might mean there’s a leak or a backup of the system. When the septic tank is backed up, not only does the tank not hold the water properly, but the purification process cannot function.

Identifying The Problem

Based on your septic tank model, you might be able to figure it out yourself by following the instructions in the manual or given to you at the time of installation. You may need to check in with your septic tank service professional to have an inspection and be sure everything is in working order, or if repairs are required, they are attended to in a timely manner.

If grass won’t grow over the septic tank, one of the more simple problems may be that the soil above the tank simply is too shallow for the grass roots to thrive. Soil can become compacted over time or rinsed away slowly with rain. This can be solved by adding soil on top of the leach field and spreading some new grass seed to fill in the root system and fortify the grass.

Drain Field

What Issues Might Occur

When the septic tank malfunctions, a few issues can occur that are beyond the plumbing system itself:

  • The buildup of wastewater in the soil can lead to lower oxygen in the area, which is bad for people, pets, and grass.
  • If wastewater isn’t purified enough before reaching the soil, it can contaminate any groundwater sources, including drinking water
  • Oversaturated soils can result in home damage: water, mold, and contaminant can cause damage to foundations and basements.

What You Can Do To Prevent Issues

Taking specific steps can help you keep your system in good working condition for the length of its lifetime.

  • Don’t put chemicals or oils into the drains, which might cause buildup or interfere with the purification process.
  • Avoid heavy traffic over the area because compaction can put increased pressure on the system.
  • Get annual evaluations by a certified local professional to keep your septic tank in the best working condition.

Author: Matt Hagens

Hi, I’m Matt the owner of Obsessed Lawn. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Learn more about me and find me on Facebook.