Why Does Soil Sink in Yards or Garden? (6 Reasons)
The soil you are stepping on is like everything else in nature – it changes. The ground in your yard erodes, rots, and is carried away, making it look like your yard is sinking.
In general, sinking soil in a yard or garden is often a natural phenomenon caused by 1) organic matter breaking down, 2) soil compaction, 3) erosion, 4) voids or sinkholes, 5) overwatering, and 6) drainage. This can be easily fixed by adding more soil or placing more plants in the yard.
The soil in our yards changes and this will inevitably affect our plants. To keep a happy and stable growing environment for our garden, we have to know the reasons why soil sinks and how to solve them.
1 – Organic Matter Breaking Down
The organic matter in the soil decays and breaks down, reducing the total volume of the soil. The broken-down organic matter produces holes in the soil that later collapse, causing the soil to “sink.”
Soil is composed of minerals, organic matter, water, and air. Even if organic matter (decomposing materials from living organisms) only composes 5% of the soil’s total volume, the effect is noticeable since these can create gaps between the soil.
Solution: Adding soil with more minerals and less organic matter is recommended to prevent soil from sinking. However, this may not provide the proper nutrients for your plants.
2 – Soil Compaction
Foot traffic, vehicle movement, limited crop rotation, and even gravity can cause soil in yards to compact. This gives it the appearance of sinking but in reality, the soil is becoming more tightly clumped together.
Soil compaction is a natural phenomenon that is no cause for alarm. You can see it in natural dirt paths that animals traverse through. The dirt path is often barren and sunken compared to the rest of the landscape.
Areas that do not even receive any foot traffic such as flower beds are also affected by compaction due to gravity or excess water, causing the soil to become heavier and collapse under its own weight. Particularly harsh and rainy climates can also produce this effect.
Solution: Adding more soil and preventing passage will prevent soil from compacting. A small sign or a rock path will help direct passage to minimize the effect.Miracle-Gro Raised Bed Plant Food, 2-Pound
3 – Erosion
Wind and running water are other causes of an apparent reduction of the soil level that can be confused for a sinking yard. This is common in areas that are typically windy and rainy (like the north of the UK and Hawaii in the USA).
There are three main forces in erosion: 1) water, 2) wind, and 3) ice. Water is the most prevalent of the three forces responsible for causing most of the erosion on Earth. These are completely natural processes that cannot be completely prevented.
The most that we can do to prevent erosion is to reduce its effects by planting cover crops, mulching, or adding a new layer of soil over the yard. These are traditional agricultural techniques that have made their way to gardens and yards.
Solution: Stabilize the soil by allowing perennials and grass to grow over the barren patches. Adding rock over the soil can prevent the finer soil matter from being carried away by the wind. Mulching (adding layers of material over the ground) can also help prevent erosion).
4 – Voids or Sinkholes
Voids are empty spaces below the surface that can collapse, causing the topsoil to sink. Sinkholes occur when soluble bedrock (i.e. soluble matter eventually gives way, causing small to giant holes on the topsoil).
Void is a general term whereas sinkholes are a subcategory of it. Voids are beneath the surface whereas sinkholes appear on the surface, creating large holes that reach the bottom. Sinkholes are caused when soluble matter collapses soil above it while voids are caused by the naturally occurring spaces between soil due to washouts or gaps. To note that you will probably (and hopefully) never see sinkholes as they are rarer.
Solution: Voids can be detected with microgravity surveys and then cover the sunken area with more soil. Sinkholes can be fixed with concrete, sand, and an additional layer of soil. However, major sinkholes in yards near the foundations of homes may need professional help.
5 – Overwatering
Overwatering, as a form of erosion, causes the soil matter to be carried away to other places. It also causes the soil to clump together more easily and weigh heavier, making it more susceptible to sinking.
Unlike the other reasons, overwatering can be a man-made problem. This means that they can be remedied by making sure watering is carefully done so as to not allow the soil to sink or drown the plants.
Solution: Drainage holes, canals, or any other method that allows excess water to exit the soil. Keeping a detailed watering schedule based on the seasons can prevent negligent overwatering.
6 – Drainage
Drain canal walls without rocks or cement lining or walls lower than the landscape may cause the surrounding soil to be carried away due to water erosion.
Though drains are generally good in the field of gardening to prevent plants from drowning or the ground from becoming too moist, an improper implementation may cause more trouble than good.
Solution: The walls of the canals should be cemented or lined with stones. These walls should be slightly higher than the surrounding landscape to allow overflowing water to pour in without carrying away too many soil particles.
Sinking Soil: Easy Solutions
Sinking soil is fixed by 1) just adding more soil and 2) overseeding the soil with grass to help the surface soil from being carried away by the elements.
It’s also possible to find soil with less organic material to reduce the effects of sinking due to decomposition. However, this will lead to less nutritious soil for your plants. It will be better to find more clayey soil since these are less permeable.
The tips above also apply to potted plants since they also follow general principles. It’s still soil after all!
Plants That Prevent Erosion
Cover crops are plants that are planted in the soil to cover any bare earth to prevent soil erosion, soil fertility, weed control, overwatering, and pests. Examples of cover plants include grasses (forage gains), Sesbanas, Azollas, Periwinkles, and Crawling Junipers, among others.
Cover crops are often used in conjunction with mulching and grassing to further mitigate the effects of erosion and, by extension, soil sinking. Apart from preventing erosion, cover crops have the added benefit of increasing the biodiversity of the garden, making the soil healthier and less prone to weed invasion.
Average Rate of Sinking Soil Per Year
The average rate of sinking soil varies on the geographical location, the geological composition of the ground underneath, and the prevailing climate. The average rate can range from 0.75 to 2 inches per year.
There is no sure-fire method to determine an exact rate due to the numerous complex factors but most gardeners shouldn’t be too worried about their yards sinking.
Serious soil sinking often occurs in areas where there is excessive groundwater extraction like in the farms of Corcoran, Californian. This is not the case for most residential gardens and yards that have compacted soils to serve as the foundation for homes.
Indicators for a sinking yard are: 1) the cement or laid bricks on the ground are broken up or cracked, 2) noticeable unevenness of the terrain, 3) small to large holes appearing, or 4) localized depression along the surface.
Applying Other Agricultural Techniques to Sinking Yards
Agricultural techniques have developed different ways to solve soil sinking, erosion, drainage, and overwatering, among others. These other techniques can be applied to horticulture.
- Contour farming or contour cultivation – planting crops across a slope by following the elevation contour lines will break the flow of water over the surface and promote water infiltration.
- Intercropping – planting more than one crop or plant type next to each other can reduce erosion by 26-43%. The main crop is planted with two subsidiary crops (ex. Maize with cowpea and okra).
- Mulching and Organic Matter – spreading a layer of mulch or organic matter such as grass, leaves, or manure can effectively reduce erosion by 29.4%.
- Tillage – mechanically agitating the soil by plowing, stirring, and digging, then directing water run-off can effectively reduce erosion by 6.11–64.2%.
These techniques will work on large or small yards. They’ll need a bit of creativity in implementing in yards because every yard differs from one another in terms of climate and soil composition.
Compacting Soil in Construction
Compacting soil is necessary for construction to make sure the foundations of the structure are stable. By mechanically compacting the soil, the soil increases in density and stability.
Compacted soil has significantly better load support and reduced water seepage. We can apply these principles in gardening.
We can compact the soil beforehand and then apply a loose layer of soil later for seeding and planting. Through this, the effects of sinking soil are mitigated by compacting it in the first place.
Summary of Why Soil Sinks In Yards
Soil sinks in yards due to 1) organic matter breaking down, 2) soil compaction, 3) erosion, 4) voids or sinkholes, 5) overwatering, and 6) drainage. These are mostly natural processes brought about by the elements.
Though initially alarming, the causes and remedies are equally natural. Simply 1) add more soil to add to the volume of the sunken soil or 2) add more plants to prevent the erosion of the topsoil.
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- “The Central California Town That Keeps Sinking” by Lois Henry in New York Times