Fill Dirt vs Topsoil What Are They and When to Use Each

Fill Dirt vs Topsoil What Are They and When to Use Each


If you have holes in your yard or are looking to spur on the growth of your plants, you’re probably interested in what materials are best for which task. You’ve gotten your bagged mulch, you’ve figured out the best uses for pea gravel, and you’ve sourced a landscape supply company with everything you need. How do you choose now between fill dirt vs topsoil?

What is Soil?

Soil, or dirt, is important to your landscaping, your yard, and your garden. You probably know this already. Healthy soil will contain approximately 25% water, 25% air, 5% organic matter, and 45% mineral content. About 0.01% of Earth’s water supply is stored within the soil, and soil for gardening and landscaping purposes is typically evaluated by its fertility and its texture. All soil is a remnant of Earth’s earliest days, when the primordial formations began to cool and the surface broke down into rocks, pebbles, and finally much smaller grains. Life was born, lived, and died on these rocks. As they died, carbon-based life forms began to add organic matter to the mix.

Fill Dirt vs Topsoil: Characteristics

If you were to dig up a spot of ground, in most places it would be easy to tell that the top layer is much richer than layers underneath. This top layer can be several inches to several feet deep, and the thing that makes this layer different is the amount of organic matter within it. This rich soil is known as topsoil. Underneath it is what we could call fill dirt. Fill dirt may contain topsoil, but it also contains a lot more rock and other inorganic materials.

Fill Dirt vs Topsoil: Topsoil

The first four inches to a foot of soil contain almost all the nutrition that plant roots need to thrive. Topsoil is rich in nitrogen, carbon, and nutrients and allows light and air to penetrate while still retaining moisture for the benefit of plants. A study done by the University of California found that plants grown over topsoil were 250% heavier and richer than plants planted on fill dirt, even when the same seeds and the same fertilizer were used. Additionally, while plants planted on healthy topsoil tended to thrive, plants on fill dirt tended to die out in three to five years.

Fill Dirt vs Topsoil: Fill Dirt

Fill dirt may not be as rich as topsoil, but it is also important to our world. Fill dirt can be made up of many different things, and it provides the basis for foundations and support for the deep roots of trees. While topsoil will tend to sink over time as organic matter within it decomposes, fill dirt retains its integrity.

Fill Dirt vs Topsoil: When to Use Each

From this description, you might wonder what is fill dirt for and whether it wouldn’t be better to simply plant everything in topsoil. Topsoil, however does not make an excellent choice for your garden. Topsoil is a great choice for your lawn, but garden vegetables and flowers generally require different amounts of nutrients and a different system from what a lawn can thrive on. You’ll need to make sure that your topsoil is the right kind if you want to use it for your garden. Topsoil is also an excellent choice if you need drainage. Fill dirt, on the other hand, is the best choice for dealing with an uneven lawn and is the superior choice for contouring, raising grades, and filling out holes. Fill dirt is also excellent for building up landscaping to the levels you desire or raising low points in the lawn so they don’t become so wet in the rain. Fill dirt is also essential to septic systems and many construction projects.

There are many types of soil out there for gardening and landscaping use. Before you buy, make sure you know what you’re using it for and which type of soil is best for your needs.