Fill Dirt vs. Topsoil: Differences and Which to Use

Fill dirt and topsoil have a variety of uses, each having qualities that make them best-suited for particular landscaping or gardening projects. It's sometimes even possible to get fill dirt for free. Fill dirt is a combination of natural materials, like rock, sand, and shale, used to—you guessed it—fill in a hole or change property elevation. Topsoil, on the other hand, is dirt fortified with nutrients usually used for gardens and grass.

Learn about all the differences between fill dirt and topsoil and which would be best to use if you're undertaking a land-grading project, starting a new planting bed in your yard, and more.

Top Soil vs. Fill Dirt At a Glance

What Is Fill Dirt?

Fill dirt is rocky, sandy, and shaly material sourced from building and construction projects. Before the excavation of a foundation begins, the top layer of soil (the topsoil) is peeled off and set aside to be reused for landscaping on-site. Then, everything underneath is removed to dig the foundation. Some of that dirt is used as fill on-site, and the rest is hauled away and made available as fill dirt.

Fill dirt isn't something you'd want to plant your garden plants in (because of all the stones it contains; plus it lacks organic matter), but the benefits of fill dirt are exploited to serve several purposes. The abundance of stones makes fill dirt ideal for raising and leveling land, because they fill up space. The rockiness of fill dirt also makes it ideal for building up ground to fix water drainage issues, because water percolates well through it. Another benefit of fill dirt is that, compared to topsoil, it is relatively inexpensive.

What Is Topsoil?

Topsoil is just that—the top layer of soil in a garden or landscape. It's a rich mixture of minerals and organic matter that's vital for growing trees, shrubs, flowers, and vegetable gardens. It's also pricier than fill dirt because of its relative scarcity and desirable content.

When to Use Fill Dirt vs. Topsoil

Fill dirt is always used as the bottom layer, followed by a layer of topsoil. For example, if you were filling in a hole, you might use 2.5 feet of fill dirt and cover it with 6 inches of topsoil. Beyond that, there are specific uses for fill dirt vs. topsoil:

When to Use Fill Dirt

Just as the name implies, fill dirt is used to fill up space. Being less expensive than topsoil, it also serves as a foundation for the latter. Especially in the case of plants with larger root systems, such as trees, the ground needs a certain amount of depth, both for roots and for drainage.

Enter fill dirt, which can be used in the following ways: for filling gaps when packing around the stones in retaining walls, filling holes when erosion has washed away ground and you need to patch the area, and reshaping a landscape, as sometimes your design plan calls for changing the contours of a yard, such as smoothing out a steep slope.

Even if you had no budget constraints and unlimited access to high-quality topsoil, you would still use fill dirt in these situations because it drains much quicker than topsoil.

When to Use Topsoil

Topsoil is the layer on top of fill dirt; it's what you plant in. It is most often used when starting a new garden/lawn/planting bed, replenishing soil after the growing season, or replacing current topsoil that has been washed away from heavy rain.

These are some general guidelines for how deep a layer of topsoil should be:

• For lawns: 4 to 6 inches
• For planting beds: 6 to 8 inches
• For vegetable gardens: 6 to 8 inches
• For foundation plantings: 6 to 8 inches

Other Fill Dirt Options

Gravel is an aggregate of small rocks, and it looks great as filler between the more prominent rocks in rock gardens. As a fine, granular material, sand is perfect for projects such as paver walkways or patios, where it serves as an even foundation for your pavers. Sand and gravel are sometimes mixed for use in backfilling projects, especially those that need sharp drainage.

Testing and Amending Fill Dirt  

If you're starting a garden and can't afford topsoil, you can amend your fill dirt. Begin by testing it for nutrient deficiencies and excessive acidity/alkalinity. Once you know what nutrients your dirt is deficient in, you'll be able to start working to improve it with free amendments. Once you know how acidic/alkaline your dirt is, you can lower the soil pH or raise the soil pH.

Where to Get Free Fill Dirt 

You can buy fill dirt at a home improvement store or from local sand, gravel, or mulch suppliers. But, if you need a lot of it, the cost can skyrocket, though it still costs significantly less per cubic yard than topsoil. Here are some of the best ways to find free fill dirt and what you need to do before you haul it home:

Visit Construction Sites

At any construction site, they'll have a lot of dirt to haul off when they're done (and they're probably expecting to pay to dump it). Ask if you can have it; they might even deliver it to your home for free. To ensure it's not contaminated, ask:

• Was an environmental site assessment done on the dirt?
• Is there any concern about the site from which the dirt originated?
• Has the dirt been screened, or does it still contain large pieces of roots and rocks?

Check Online Dirt-Matching Sites

Construction, excavating, and landscaping companies have turned to posting their excess soil inventories online via dirt-matching sites. Some sites are only local, and the national sites just need your zip code or address. Many of these sites are open to homeowners as well. Try these favorites:

• DirtFill.com
• DirtMatch.com
• FillDirtConnections.com (local in Virginia)
• Craigslist.org (search for fill dirt; you may find free delivery, too)

Befriend a Farmer

Manure is a great amendment for your garden soil, and it's readily available. Jump on Craigslist or Freecycle, and you'll find lots of ads for free horse or chicken manure. Just know that you'll need to make compost before you can use it in your garden. Want something you can use right away? Then, look for rabbit manure. It doesn't have to be composted first.

Check Your Local Town Hall

Call your town hall, and ask if there is a local fill dirt program. Chances are there's an area at the local town dump set aside for fill dirt. You may find there are restrictions on how much you can take, and you'll have to find your own way to haul away the dirt. 

Sources to Avoid

When it comes to certain sources, free dirt may be free for a reason. Avoid fill dirt or topsoil that is potentially dangerous or contains rhizomes of a weed such as Japanese knotweed (Polygonum cuspidatum) by passing on these sources of dirt:

Ditch Cleanouts

Road crews are happy to give away the dirt that they dig out of ditches, but it'll usually come with lots of litter, weed seed, and environmental contaminants from all the vehicle traffic.

Waste Management Plants

"Biosolids" (what's left after sewage sludge is processed) may be free. But, while the process is regulated, they may contain chemical residues from prescription medications and household cleaners.

Potentially Contaminated Sites

Old home sites, urban lots, and industrial areas are likely to be contaminated with dangerous levels of heavy metals and hazardous materials, so it's best to pass on any dirt from these places.

Unknown Sources

Make sure you know where the fill dirt came from. If you have any questions about its quality or safety, take a soil sample, and have it tested.

Choosing the Best Option for Your Yard

They may both get you dirty, but there's a world of difference between fill dirt and topsoil. Topsoil, teeming with the life of organic matter, is what your plants crave. But fill dirt, which you often can get for free, provides a drainage-friendly base for it. Moreover, fill dirt is indispensable for everything from hardscape projects to filling holes to changing the elevation in your yard. Both are important, but, because each has distinct qualities and benefits, it is critical to know when to use the one rather than the other.