So, you’ve finally decided to roll up your sleeves and dive into your next big garden project. It’s exciting, challenging, and no doubt physically demanding, but the reward will make all the hard work worthwhile: a stunning backyard oasis. While your initial thoughts may center on the design and the plants, there’s an unsung hero in every great garden project—dirt.
Yes, dirt. It may seem simple or even like an afterthought, but dirt is easily one of the most important components for any successful garden transformation. The type and quantity of dirt you choose, however, will directly impact the project’s outcome. Get it wrong, and you could end up with stunted plant growth, poor drainage, or even structural issues down the line.
In this blog, we’ll discuss the types of dirt you’ll need to consider, how to differentiate between them, and some inspiring garden project ideas that heavily rely on using the right kind of soil.
Types of Dirt: Topsoil vs. Fill Dirt
When it comes to garden projects, dirt isn’t just dirt. You’ll primarily need to get familiar with two distinct types: topsoil and fill dirt.
Topsoil: Fertile Soil for Growth
Topsoil is the uppermost layer of soil, rich in organic matter and nutrients. It consists of decayed organic material, minerals, and microorganisms that are vital for nurturing plant life. Because of this, topsoil is the go-to choice for projects where plant growth is prioritized, such as:
- Flowerbeds
- Lawns
- Vegetable gardens
- Raised planting beds
The rich, moist texture of topsoil helps plants thrive by providing them with the necessary nutrients to reach their full potential. It also helps retain moisture, which is beneficial for plant health, and is crucial for establishing thick, lush lawns.
However, while topsoil is excellent for projects that involve growing plants, it has its limitations, particularly when it comes to stability. Its high content of organic materials makes it prone to shifting and settling over time. This is why topsoil should never be used in projects involving construction or heavy structural support, as it will eventually erode or compact, compromising the strength and stability of the foundation.
Fill Dirt: For Stability and Solid Foundations
Fill dirt, on the other hand, is made from subsoil—the material found beneath topsoil. Unlike topsoil, fill dirt contains little to no organic material. Its composition is mostly made up of clay, sand, and small rocks, which give it a sturdy, compactable nature. Fill dirt is used for projects that require stability and structural integrity, such as:
- Building foundations
- Land grading
- Filling holes or low points in landscaping
- Supporting hardscapes like patios, walkways, or retaining walls
Due to its density and lack of organic matter, fill dirt does not settle or shift as topsoil does, making it great for creating solid, reliable surfaces. However, it’s not suitable for growing plants, since it lacks the essential nutrients plants require.
Using Both Topsoil and Fill Dirt Together
In many garden projects, a combination of both topsoil and fill dirt is essential. For example, if you’re shaping the landscape of your yard with berms or terraces, you would first use fill dirt to create the basic structure and form, then finish it off with a top layer of topsoil where needed—especially in sections where plants will be added.
3 Inspiring Garden Projects Using Topsoil and Fill Dirt
Whether you’re designing a flowerbed or building a terraced garden, understanding the role of each type of dirt can help you execute your vision effectively. Here are three exciting garden project ideas that will require both topsoil and fill dirt to bring to life.
1. Berms (Manmade Landscaping Mounds)
A berm is essentially a manmade hill that adds dimension and visual interest to an otherwise flat garden. Berms are often used to highlight specific areas of the garden, divert foot traffic, or create a natural privacy screen around seating spaces. They can also serve a practical function, improving drainage by diverting water away from problem areas.
Here’s how dirt plays a role in creating a berm:
- Fill Dirt: The majority of the berm should be made up of fill dirt to provide structure and stability. Because berms are meant to maintain their form over time, fill dirt’s stable, compact nature is key to preventing erosion or sinking.
- Topsoil: After forming the structure with fill dirt, cover the berm with a thin layer of topsoil. The top layer of about 12 inches (or 1 foot) will allow you to plant shrubs, flowers, and small trees.
2. Terraced Landscaping
Terraced yards feature multiple levels or “steps” that cascade down a slope, often supported by retaining walls. This form of landscaping is both functional and beautiful, helping reduce soil erosion, especially on steep slopes, while adding depth and interest to your garden.
Here’s how to properly use dirt in a terraced garden:
- Fill Dirt: Use fill dirt to create the base layers or foundation of each terrace. Fill dirt is compactable and helps ensure the longevity and strength of each terrace.
- Topsoil: On top of the fill dirt, add a few inches of topsoil, particularly if you plan to plant flowers or vegetables in each terrace.
The topsoil will provide the nutrients necessary for healthy plant growth, while maintaining the overall design.
3. Raised Garden Beds
Raised garden beds are increasingly popular for both decorative and functional gardens—particularly for those who enjoy growing their own vegetables. They allow better control over the quality of the soil and are easier to maintain than traditional in-ground beds. Raised beds also help to manage areas with poor soil quality.
Here’s how dirt is distributed in raised beds:
- Fill Dirt (Optional): If your raised bed is very tall (over 12 inches high), you might want to use fill dirt to fill the lower part of the bed. This saves you money by not using expensive topsoil for sections of the bed where roots won’t reach.
- Topsoil: The top 6-12 inches of the bed should be filled with nutrient-rich topsoil, where plant roots will grow. This will help your vegetable plants or flowers thrive, yielding abundant crops and lush greenery.
How to Calculate How Much Dirt You Need
Once you have a clear plan for your garden project and know which type of dirt to use, the next step is figuring out how much dirt you’ll need. Dirt is typically sold by the cubic yard, and to calculate the volume required, you’ll need to measure the length, width, and depth of the area you’re filling.
Here’s a quick formula to help you figure out how much dirt you’ll need:
- Measure the length, width, and depth (in feet) of the area.
- Multiply the length by the width and depth to get the total volume in cubic feet.
- Divide the total cubic feet by 27 to get the total cubic yards (there are 27 cubic feet in one cubic yard).
For example, if you’re filling a 10-foot x 10-foot area with dirt, and you want the depth to be 1 foot, your total dirt volume would be 10 x 10 x 1 = 100 cubic feet. So, 100 cubic feet divided by 27 equals approximately 3.7 cubic yards of dirt.
Get In Touch with Northern Virginia’s Dirt Experts
Whether you’re building a berm, creating raised garden beds, or tackling a larger landscaping overhaul like a terraced yard, understanding the difference between topsoil and fill dirt is crucial to your project’s success. Topsoil is essential for plant growth, while fill dirt provides stability and lasting support for your landscaping structures.
Don’t forget to calculate how much dirt you’ll need for your next project. And, of course, make sure you’re sourcing high-quality soil types to ensure the health and longevity of your plants and garden structures. If you’re unsure about how much dirt to order—or the specific type you’ll need—reach out to a professional service like Dirt Connections, where experts can guide you through the process and ensure timely delivery of the right soil for your project.
