Understanding Soil Compaction & Why it Matters
To understand the how’s and why’s of soil compaction, it helps to understand what soil is. Today we’ll be talking about compaction that occurs in the Upper Limit of soils, since that’s the area most homeowners are aware of and struggle with.
Basically, compaction is packed earth.
Healthy soil isn’t as solid as it seems– it’s actually a complex mixture of organic matter, minerals, liquids, and gasses that create a matrix of pores and pockets. Plants take advantage of the open spaces in these matrices to extend their roots in search of nutrients and water. (Check out this time lapse of a pea shoot germinating to see how roots navigate these pores!)
When heavy equipment or regular foot traffic travels over an area of soil (like your lawn) the combined forces of weight and gravity can cause the soil to become compacted, losing those all important pockets of air and water which support healthy plant growth and development. Ultimately, your landscape suffers as a result.
What’s the big picture?
Increased storm runoff and erosion: The lack of pores in compacted soil prevents water from being absorbed into the ground, meaning you’re more likely to see water pooling on the lawn and/or an increase in the amount of water rushing to the nearest low point (hopefully not your basement!). The increase in water flow can create problems with erosion and in some cases, overwhelm an already overburdened neighborhood storm drain system. The lack of ground penetration can also reduce the moisture content of your soil over time, leaving your plants parched and begging for a drink.
Stunted plants: Plant roots typically grow to and through the open spaces in soil, taking up the available oxygen, water, and nutrients in and around themselves. When the soil around plant roots becomes compacted the plant has to create a greater amount of force to push through. As a rule of thumb, plants with struggling roots will have smaller tops – there just isn’t enough energy and nutrients to support it!
Shallow Root Systems: When plants encounter layers of compacted soils below, they often respond by spreading their roots out instead of down, creating a shallow network of roots that’s known as the “pancake effect”. Because of their shallow roots, these plants are easily uprooted and more prone to root damage from fluctuations in temperature or damage from foot traffic.
Nutrient Deficiencies: All plants – trees, shrubs, flowers, and crops – run the risk of nutrient deficiencies when grown in compacted conditions.
It doesn’t “just go away”: While the natural forces of Nature can and will reverse the compaction over time, it can take years before significant improvement visible. To put it in perspective, studies show that a 1 time compaction event in agricultural fields can result in reduced crop yields as much as 12 years later.
3 General Approaches to Dealing with Soil Compaction
Avoid: Two of the biggest contributors to soil compaction are heavy equipment and working at the wrong times. As much as possible, try to avoid using or driving any kind of heavy equipment or vehicles around your home. As simple as it sounds, it’s a leading cause for compaction on residential properties (and can also end in broken drainage tiles!)
Another common contributor is working on the property when the ground is wet, as soil is more susceptible to compacting when it’s wet or soggy.
Alleviate: If you’re dealing with ongoing construction or are planning a big improvement project, it can be downright impossible to avoid using heavy equipment around the house. Alleviate future issues by identifying key areas to avoid (like drainage and irrigations systems) and direct traffic around them as much as possible. As an added benefit, limiting traffic to specific areas makes it easier to ID areas that need a little TLC when it comes time to aerate.
Accept: The ever present “do-nothing” approach. Nature will eventually alleviate the problem on its own – but it may take a long, long time to do so.
Managing Compacted Soils in Garden Beds
Over time the soil in garden beds can become compacted from repeated heavy rainfalls and foot traffic, making it difficult for plants to absorb the water and fertilizer you’re throwing down. One of the most effective ways to deal with compaction in planting beds is to spread a 2” layer of an organic mulch each year (or two). The mulch acts as a buffer against compaction forces and as it breaks down, it provides nutrients improves the overall quality of your soil; win-win!
Top Tip: As mulch breaks down over time, it can start to look a little concrete – use a rake to gently break up and redistribute the top 1” of mulch. “Refreshing” the mulch allows more water and air to penetrate the upper limit of soil, and it often looks like a whole new application too! If you’re working in an area that’s tightly planted, children’s and pooper scooper rakes work remarkably well!
Managing Compacted Soils in the Lawn
Lawns face many of the same compaction issues as garden beds, with heavy rains and regular foot traffic compressing soils over time. This stresses the turf, reducing its ability to respond to environmental changes (like temperature fluctuations and drought) and compete with weeds, leading to the overall decline of the lawn’s aesthetic.
Soil compaction in lawns is handled differently than in garden beds for practical reasons – can you imagine mulching an entire yard? We couldn’t either. Instead, homeowners are encouraged to core aerate every 1-2 years, depending on the severity of the soil compaction on their property.
Is a simple process that uses an Aerator machine to perforate the soil at set intervals, creating small holes that allow water, oxygen, and nutrients to reach the roots while breaking up dense layers of thatch (which also blocks water and nutrient movement). The end result is usually a fuller lawn with increased drought and pest tolerance. To learn more about the cost of core aeration, we recommend contacting your neighborhood landscaping company as prices will vary depending on property size and a few other factors.
Check out our blog: Should I Aerate and Overseed this Year to learn more about Aeration!