What Causes Compacted Soil?

excavator on top of grass

Compacted soil is a common issue with lawns. It can affect plant growth and damage your yard. But what causes compacted soil? A combination of factors can result in this soil condition, including heavy foot or vehicle traffic, low organic matter, intense rainfall, overwatering, mixing clay soil with sand, and putting weight on the soil.

Reasons why you have compacted soil

illustration showing good soil vs compacted soil
Infographic by Juan Rodriguez

Compacted soil can make lawn care challenging and affect soil, grass, and plant health. Here are some of the main reasons why your soil is compacted.

Heavy foot or vehicle traffic

When people repeatedly walk, run, or drive over the same spot, or when pets use the same track, the soil gets squished and packed. The same goes for placing heavy machinery on the soil during home renovations, construction, or landscaping projects.

This reduces the space between soil particles, making it harder for air, water, and nutrients to move through them. It also can result in poor plant growth, increased water runoff, and soil erosion

Low organic matter

Soil low in organic matter is more likely to become compacted over time. Organic matter, such as decomposed leaves, grass clippings, plant trimmings, mulch, or compost, mixes with the soil and creates pockets for air, water, and nutrients to flow. 

Without it, the soil becomes harder and less flexible, resulting in compaction, drainage issues, and poor plant growth.

Intense rainfall

Another factor that can compact your soil is heavy or prolonged rainfall. As the rain pounds down, it pushes soil particles together, leaving very little space for air, water, and nutrients. When this happens over and over, your soil can become so dense that it won’t allow grass or plants to grow.

Overwatering

Man watering green lawn, sprinkling water on the grass with water pistol
rh2010 | Adobe Stock Free | License

When you overwater your lawn or garden, the soil becomes saturated. As the gaps between the soil particles fill with water, particle movement decreases or disappears, causing compression.

Wet soil is also softer and more vulnerable to pressure. As water becomes a lubricant, the particles squeeze closer together, especially when you walk over the soil or operate different machinery.

Waterlogged, compacted soils drain very slowly, leading to persistent moisture, more compaction, and possible pest and disease issues.

Mixing clay soil with sand

Clay soil has tiny particles that are sticky and more prone to compaction when wet. In contrast, sandy soil has larger, coarser particles that don’t stick together and allow better drainage. 

If your soil has too much clay, you may think adding sand will fix the problem. But this usually produces a concrete-like material that is impossible to work with.

“No amount of sand added to a clay soil will change its texture,” says Linda Brewer, senior faculty research assistant in Oregon State University’s College of Agricultural Sciences. “The large sand particles provide a surface onto which the tiny clay particles adhere. The result can be more difficult to manage than the original clay.”

Too much tilling

When you till, you break up and turn the topsoil in preparation for planting. It’s beneficial because it improves soil structure and incorporates organic matter into the soil.

However, over-tilling can cause problems if done incorrectly and at the wrong time. 

If the soil is too wet when you till, it can become sticky and clumpy. If it’s too dry, tilling will break it into unmanageable chunks.

Over-tilling can disturb the soil’s structure, reducing its ability to store moisture and nutrients and harming beneficial organisms that keep it in good condition.

FAQ about causes of compacted soil

How can I fix compacted soil?

To fix compacted soil, aerate the soil, add organic matter, reduce foot traffic, and water your lawn or landscape correctly. A combination of these efforts can significantly alleviate compaction and revive your yard.

What are the most obvious signs of compacted soil?

Some tell-tale signs of compacted soil include:

  • Unhealthy grass
  • Limited grass or plant root growth
  • Poor drainage
  • Hard, crusty soil surface
  • Difficulty digging or tilling
  • Increased soil erosion
  • Low microbial activity
  • Weak seed germination
  • Weed growth
  • Pest and disease attacks

How does compaction affect healthy soil?

Healthy soil typically consists of 50% solids, 25% water, and 25% air, says the University of Florida IFAS. If the soil starts to compress, those percentages change; the less air and water moves through the soil, the more erosion, runoff, and poor water infiltration happens.

Say goodbye to compaction

Knowing what causes compaction can help you maintain healthy soil and a thriving landscape. It can also help prevent issues down the line.

Not sure if your outdoor activities are contributing to soil compaction? A local lawn care expert can offer guidance and help with additional services, including aeration, dethatching, fertilization, and overseeding.

Main Photo Credit: Biewer_Jürgen | Adobe Stock Free | License

Andie Ioó

In my free time, I enjoy traveling with my husband, sports, trying out new recipes, reading, and watching reruns of '90s TV shows. As a way to relax and decompress, I enjoy landscaping around my little yard and DIY home projects.