Compacted Soil: Causes and Cures for Your Lawn

Healthy soil (left) vs. compacted soil

Your lawn was meant to be used — but maybe you have used it too much.

Maybe it has become:

  • A staging area for that van you’ve been trying to sell.
  • Where you practice your short game.
  • Basepaths where your kids re-enact the World Series, every day.
  • Your dog’s workout room

That traffic takes its toll, creating compacted soil. As tires roll and feet and tramp on the grass, the soil underneath becomes denser and denser.

Soil compaction leads to turf thinning, tearing, injury and even death from crushed stems, leaves and crowns.

While the other symptoms may be obvious, compaction happens out of sight. When the soil loses that large pore space, it can’t transport water, air and nutrients that grasses need. As a result, plant growth is limited and the grass suffers.

Do You Have Compacted Soil? How to Tell

Should you be worried about soil compaction in your yard?

“Well, it depends,” says Horticulture Agent Laura Miller with the Texas A&M Extension in Tarrant County.

Most often, home lawns see soil compaction with frequent, regular pressure such as parking a car on the lawn. Maybe the dog in the backyard has a track that it runs over and over again.

Riding lawnmowers can also contribute, but just once or twice a week over the turf shouldn’t be enough by itself to leave you with overly compacted soil, she said.

It’s a bigger problem for public spaces such as ball fields and parks, which that see intense traffic. But homes aren’t exempt.

What Compaction Does to Your Soil

Compaction causes the destruction of soil structure. And that’s bad news for your lawn.

Most compaction happens in your lawn’s root zone, the first two or three inches below the soil surface.

Soil density increases. Air can’t move through it, resulting in a buildup of carbon dioxide and other gases toxic to grass roots.

Water can’t soak in either, increasing runoff and reducing water infiltration in the soil and stopping water intake by the grass roots. Temperature highs and lows can become extreme.

And there’s more open space down there than you think.

Your Grass Needs Wide Open Spades

Healthy soil has pores, leaving room for air, grass roots — and beneficial earthworms.
Healthy soil has pores, leaving room for air, grass roots — and beneficial earthworms.

Half of a healthy soil’s makeup is pore space. Very dense soil stops roots from getting to the water, nutrients and structural support they need.

Compaction also brings a host of other problems, explains the University of Massachusetts Center for Agriculture, Food and the Environment.

First, low shoot density encourages the encroachment of weeds and disease activity.

The low rate of nutrient uptake means an increased fertilizer regimen to keep your lawn healthy. But, UMass says, that can make a bad situation worse, since the problem isn’t a lack of nutrients but the root’s inability to absorb them. Adding nitrogen can further reduce the turf’s rooting potential.

For the same reason you need to fertilize more, you may need to irrigate more. And with the increased stress, your grass will become less resilient to environmental factors like drought, heat and cold.

4 Ways You Accidentally Compact Your Soil

According to Michigan State University’s guide “What to Do About Compacted Soil,” there are four ways that homeowners and turf managers can cause their dirt to pack too tightly:

1. Over-Tilling

Does your soil resemble an alligator’s skin? You may have tilled it too much. Making several passes with a tiller breaks down the desirable clumps of small aggregates that let air and water pass through, encouraging root growth. If water ponds up and leaves behind a linear pattern of cracked soil, it’s a sign of over-tilled soil.

2. Working on Too-Wet Soil

Don’t work in the soil when it is too wet, because that can also compact it excessively. In the spring, before tilling the garden or turf area, take a handful of soil and compress it into a ball. Then give it a poke. It should crumble. If it doesn’t, the soil is too wet.

3. Mixing Sand Into Clay Soils

“My soil is too clayey,” you say. “Aha, I’ll add sand.” Wrong move. Adding sand to clay creates a compact mass that’s like concrete. Instead, loosen the soil with organic matter such as compost or peat moss.

4. Compressing Soil WIth Weight

Heavy machinery or vehicles parked or driven over an area, home construction or rebuilding — even heavy repeated foot traffic — can compact soil. It could be a riding mower’s tires running over an area repeatedly.

Warning Signs of Soil Compaction

Healthy moist soil (above) forms clumpy aggregates when moist, compared to dry compacted soil (below). USDA Photo by Lance Cheung.

Soil compaction happens more often in the spring when conditions are wetter and heavy rains more frequent.

Look out for a place where weeds have begun to take over.

Some types of weeds, such as goosegrass, do better with compacted soils, Miller said. Sometimes that weedy patch is a sign that the soil underneath is compacted.

Some grasses like Bermuda are tough and hardy when it comes to compacted soil, she added, but even Bermuda won’t be as happy as a weed in those conditions.

It can also be a problem for other plants, like trees, she said. Folks may see a declining tree in their yard but not think the problem is compacted soil hampering the plant roots from their favorite shady parking spot.

Implement Traffic Control

Golf carts, riding lawnmowers, cars and even bicycles and foot traffic all compact soil to some degree.

Controlling the what, when and where of that traffic can protect your soil.

Proper operation of motorized vehicles makes a difference. Avoid quick starts and stops and sharp turns. Don’t drive on your lawn when it’s too wet.

Irrigation should also be timed so the topsoil isn’t too wet when you’re expecting heavy traffic on your lawn.

Dealing With ‘Desire Paths’ and Shortcuts

Maybe your lawn sees consistent traffic in a consistent spot, like a shortcut to the bus stop for neighborhood kids.

That unsanctioned route can become a path of bare dirt thanks to the added stress and compaction, called a “desire path.” Those trails happen where pedestrians find the easiest route from A to B regardless of sidewalks.

But you have options even if that desire path ends up in an undesirable place like your lawn.

Trees and shrubs can direct traffic. Ornamental shrubs or trees can take the place of fences. You may want to go ahead and make it permanent with pavers, mulch or wood chips.

If that’s out of the question, compaction problems can be mitigated. Add some coarse sands or other materials like calcined clay where that traffic occurs.

Your lawn itself can also help stop compaction.

Cutting higher and dethatching turf can help absorb some of the pressure and keep it from compacting the soil.

Compaction Cure: Core Aeration

If your soil is compacted, lawn aeration is the best way to deal with it, Miller says.

Both solid-tine and hollow-tine aeration are good, but hollow-tine core aerating is the more effective option, she said.

A pitchfork driven into the ground and pushed back and forth may be enough for a single small area of light compaction. For larger turf areas, you’ll need an aeration machine.

The best bet is a core aerator, a machine that forces tines into the soil, pulling plugs of it out of your lawn. That creates gaps in the lawn for the root system to grow into

And when it comes to proper aeration, timing is everything. If you want your turf to recover properly, aerate when it’s still got the best of its growing season ahead of it.

Warm-season grasses can be aerified starting in late spring through late summer. Cool-season grasses are best aerified in early fall or early spring.

Spiking and slicing are two other methods, but they don’t actually remove any soil from the lawn. For that reason, spiking and slicing can actually compact the soil further.

After You Aerate, Add Topdressing

Topdressing after aeration can help in the long run, says Miller. Topdressing is simply adding a small layer of sand, compost or a mix of the two over the top of your lawn.

Topdressing will help even small areas, can improve drainage and reintroduce microbes to help deal with future thatch buildup.

If you used a core aerator, simply rake over the exposed plugs. Breaking them up turs them into a topdressing.

Be careful about using a topdressing that’s too different from your base soil, Clemson University Extension says in its turfgrass cultivation guide. “Heavy topdressing over time can create a layered soil causing a reduction in soil permeability reducing water infiltration into the turf root zone,” the guide says.

Around Tarrant County, Miller says, the best option is topdressing with compost, as the soils don’t have a lot of organic matter.

Adding that material can help the soil hold water and air better, she said.

Whichever you choose, be careful not to apply too much topdressing with your long-term lawn care regimen.

Excess material can create a layered soil and result in the same problems you had with compaction in the first place.

Whatever the cause, once you’ve aerated and topdressed, your soil should be able to breathe again and your grass will thank you for it.

Main image shows healthy soil with room for roots to grow (left) and compacted soil. Credit: USDA 

Derek Lacey

Derek Lacey

Formerly the agriculture writer for the Hendersonville Times-News, Derek Lacey’s articles have appeared in U.S. News & World Report, The Charlotte Observer, News & Observer, and The State. He has won 15 awards from the North Carolina Press Association and GateHouse Media, for pieces ranging from news features and investigative reporting to photography and multimedia projects.