What’s Causing the Mysterious Mounds of Dirt In My Yard?

As the snow melts away and reveals your lawn in early spring, you may discover that your lawn is dotted with mounds of dirt. You may even find yourself sinking down into the ground when you walk near these piles of soil, and that’s obviously a problem. Let’s find out who’s wreaking havoc on your lawn, and how to get rid of them!

What Does Your Mound Look Like?

Different creatures make different types of mounds. You could try taking a picture of the dirt piles and identify them using a photo search app, or just compare it to the ones listed below.  Let’s dig in!

Causes of the Mysterious Mounds of Dirt in Yard

1. Gophers

Causes of the Mysterious Mounds of Dirt in Yard

Gophers are found all across North America, so there’s a good chance that these rodents are the culprits. They spend most of their life below ground, so you’re not likely to see much in the way of holes, just mounds of dirt 2 to 3 feet (60-90 cm) across, and usually in a rough horseshoe shape, with an off-centre plug of soil blocking the entrance hole.

In their underground tunnels, which can spread out for 6 feet (1.8 m) around a mound, they pull plants down by their roots. Because they don’t hibernate, they spend their winter months down in those tunnels chowing down on your landscape plants. You may have quite a lot of damage by the time the winter snow cover is gone.

2. Moles

common lawn pest

Moles are another extremely common lawn pest in North America. They leave mounds of dirt that are more circular than those of gophers and look like a volcano with a central depression when looked at from the side. They can range in size from less than 6 inches to 2 feet (15-60 cm) across. If you see evidence of shallow tunnels radiating out from the mounds, that’s a sure sign of moles.

Unlike vegetarian gophers, moles eat insects and grubs, but cause considerable damage to your lawn in pursuit of their food.

3. Voles

tend to leave mounds of dirt behind

Voles don’t tend to leave mounds of dirt behind, but if you find a network of shallow tunnels criss-crossing your lawn, you have these critters. If you look, you may find the entrances to their burrows among the roots of trees.

Voles are plant eaters who will spend the winter nibbling on the bark of young trees and the stems of woody perennials, as well as eating grass right down to the roots, killing the plants. One female vole can have upwards of 50 young a year, so it’s imperative to not let them get out of control.

4. Ants

ants create hills

While many species of ants create hills, the size, and shape depend on the particular type of ant. Fire ants, for instance, build cone-shaped hills 6-18 inches (15-45 cm) tall and 10-24 inches (25-60 cm) across. Other species may leave a small donut-shaped mound with a central hole that is the entrance to the underground colony.

5. Worms

Worms may leave behind small piles

Worms may leave behind small piles of their castings across your lawn, usually just the size of a quarter. While their castings are nutrient-rich and are often used to feed plants, these small clumps can mar the appearance of your lawn.

6. Snakes

North American snakes are non poisonous

If you find a round hole with no mound of dirt, you probably have snakes in your yard. In most cases that’s not a bad thing; snakes will take care of any mice or chipmunks wreaking havoc on your garden, for instance. You should try to determine which snake has taken up residence, however. While most North American snakes are non-poisonous, rattlesnakes, coral snakes, and pit vipers such as the cottonmouth secrete toxins that can be fatal if a person or pet is bitten.

Read our related post on Identifying Snake Holes in Your Yard here.

Prevention and Treatment Options

Once you know which creature has taken up residence in your yard, you have different methods of dealing with them.

Animal Burrows

Natural Deterrents

Instead of pulling out the heavy artillery, start by trying to discourage burrowing animals from settling in on your property. You can start with home-made solutions to spray around their mounds.

Animals are repelled by the taste of castor oil, so try adding ¼ cup (60 ml) of castor oil to 1 gallon (3.8 litres) of water, with a few squirts of dish soap, and then spraying it around mounds, along burrows, and on any chewed plants. They also don’t like the smell of fabric softeners, so tucking a few sheets into holes may persuade them to move elsewhere. Hot pepper sprays may also work.

However, don’t use moth balls, which are often recommended. They’re very toxic and will contaminate the soil and water.

Traps and Bait

Traps and Bait

If these methods of gentle persuasion are unsuccessful, you may need to move on to other methods. Live traps are available at hardware stores in various sizes. Bait them with peanut butter for plant-eaters like gophers, or sardines for carnivores such as moles. Set the entrance to the trap over the hole.

If you choose to use a poison bait, you have 2 main options. Grain treated with strychnine or zinc phosphide will kill an animal after 1 feeding. Anti-coagulants take longer to work, but are much less toxic to children and pets. Place the bait in the main tunnel and close up the access hole. Clear any existing mounds so that you will be able to tell if your poison has done its job.

Anthills

Natural Remedies

The easiest treatment for an anthill is to pour a pot of boiling water over the mound. This will cave in the mound and kill any ants that are inside. Check back in a few days. If there’s more activity, repeat the process.

You can also mix together equal parts of vinegar and water with a few drops of dish soap, rake open the anthill, and pour it over everything. Another method involves vinegar and baking soda. Put a layer of baking soda over the nest, and then pour vinegar over top.

Be aware, however, that both the boiling water and vinegar methods will damage the grass surrounding the mound. You may prefer to use a more targeted treatment for anthills.

Chemical Treatments

One of the most effective chemicals for killing ants is borax. This naturally-occurring substance is highly fatal to ants, but not instantaneous, and that’s a good thing! Commercial borax bait is sweetened to attract ants, which will then ingest the borax and carry it back to the colony, and kill any ant that eats it. It may take a few weeks to eliminate all the ants. You can use an all-purpose insecticide to spray inside the ant colony once you’ve raked it open, but that should only be used as a last resort.

What are Some Other Potential Mounds in Your Yard?

Of course, there are other causes of mounds and holes in your yard. Here are a few to look out for.

Sinkholes

We’ve all seen pictures of massive sinkholes swallowing up houses and cars, but you may experience this phenomenon on a much smaller scale on your property.

Sinkholes can develop if the underlying rock gets worn away by underground water, causing subsidence of the sediment over top into the resulting cavity. This will create a hole as the subsoil and top soil lose their supporting layer. You can repair a small sinkhole by filling it in with a base of concrete mix, topped with clayey sand, and then sand with a final layer of good topsoil.

Sinkholes can also be caused by improperly compacted soil after construction, or broken sewer or drainage pipes. An old septic tank might collapse and cause a large sinkhole. These issues need to be repaired before the holes themselves can be filled in. If there’s an underground stream, you will need to install a French drain or catch basin upstream from the sinkhole to reroute the water safely.

Other Animals

Skunks, rabbits, and raccoons don’t tunnel, but they do dig up your lawn in search of one of their favourite foods.

They love the grubs of Japanese beetles that have become a common pest in Eastern and Central North America. Unfortunately, while it’s always nice to have fewer of these grubs and beetles, as they do considerable damage to lawns and plants, the damage caused by their predators is just as bad. Try natural controls such as bacillus thuringensis to eliminate their food source, and hopefully, they will move on.

Read our related post on 10 Easy Ways to Keep Rabbits Out of Your Yard here.

Final Thoughts

Taking care of a property is a never-ending battle against nature. While we all love to see creatures such as songbirds take up residence in our yard, other wild animals can be a destructive nuisance. Knowing how to control or eliminate these pests is key to maintaining a beautiful property.