Fixing sunken spots in the lawn

Many homeowners dedicate a great deal of attention to the appearance of their lawn. So it can be particularly frustrating when a sunken spot unexpectedly appears in the yard.

These depressions can easily throw off your footing, increasing the chances of injury for anyone working or playing in the grass. They can also lead to more difficulties in mowing the lawn, since the mower's wheels will dip into the lower spot and cause the blades to cut some patches of grass closer to the ground.

There are several reasons a depression may appear in your lawn. Identifying the cause of the problem is always helpful, and repairing the issue is thankfully a rather simple process.

Causes

Drainage issues are a common cause of sunken spots in the lawn. Woodsman Tree Service, a company in Taylor, Texas, says that if rainwater doesn't have a proper avenue to drain away, it will saturate the soil and make it more likely to settle.

Water issues are sometimes a result of problems with water or sewer lines, or the presence of an underground spring. The Fairfax County Soil and Water Conservation District in Virginia says a pipe might be leaking, or poorly compacted soil has gradually settled over time. The latter issue can cause depressions to form in areas that aren't near water lines as well.

Buried items can sometimes cause soil to sink lower than surrounding areas. Rocks can contribute to poor soil compaction, with water gradually cutting channels nearby and causing the surrounding soil to collapse inward. Tom Moor, writing for Angie's List, says buried items such as tree stumps or discarded construction debris will rot over time, with the layer of soil on time sinking down into the resulting space.

Old wells, septic tanks, cisterns, or fuel tanks may also be present underneath a depression. These items tend to be more dangerous, since they can collapse suddenly or create hazards such as jagged metal or leaking fuel.

Other activities can contribute to smaller ruts and holes in the lawn. Melissa Denney, writing for the Australian company Harden Park Laws, says following the same pattern every time you mow the law will wear ruts into the soil. Heavy equipment, such as parking vehicles on the lawn, can also create depressions.

Solutions

Repairing a sunken area of the lawn can usually be accomplished without outside help from a landscaper. It is best to do this work in the spring or early summer, since this is the best time for grass growth.

If you suspect that a buried item is causing the problem, inspect the site before commencing any repair efforts. The Fairfax County Soil and Water Conservation District says a metal probe can let you know how deep and extensive a sunken area is.

Any debris should be removed from the depression before you work to level it out. Moor says that if old stumps, building materials, or other items are the cause of the trouble, the unevenness will continue as these materials decompose.

David Beaulieu, writing for the home design site The Spruce, says that if the lawn is only slightly uneven, you can gradually level it out with a soil mixture that will support grass growth. Start by combining soil, sand, and compost. This mixture should be poured on the low areas and spread out to evenly cover the ground in a layer about half an inch deep. Keep checking the area to see if it becomes more level and supports new grass growth. You may need to add more layers of the soil mixture if the ground is still uneven.

For larger holes, you can carefully pry up any sod and set it aside for replanting. You can then add soil and moisten it to eliminate any air pockets. Then you simply need to replace the sod and water the site to help the grass take root.

It's best to fill the depression in such a way that it goes from a low spot to a slightly humped one. Moor says this allows the soil to settle into place and create a more level area.

Mixing gravel, stones, or broken bricks in with the soil can help add extra stability to the site. However, the Fairfax County Soil and Water Conservation District recommends against this step, saying water that drains through the fill can erode a larger space underneath and cause a depression to form once again.

If a depression has appeared under a patio, walkway, or other hardscaping, the repair process is more complex. You may need to pump concrete underneath the site to help level it out, or grind down the uneven pavers to make them more level.

Consult with a utility or local health department if you think the problem is being caused by a leaking pipe or an old feature such as a well or oil tank. If the issue is a result of a naturally occurring spring, you can use improved erosion control methods such as a French drain to address the problem. You might even be able to tap into the spring to use for garden irrigation and other useful purposes.

A heavily cratered lawn may need a thorough makeover. Beaulieu says this will involve regrading the site and establishing new grass, either by seeding or laying down sod.

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