What is Fill Dirt and What to Use it For?

If you’ve ever been doing any projects around the homestead involving landscaping, digging, or building, in your travels to get materials you’ve probably seen advertisements or want ads for fill dirt.

tamping the dirt
tamping the dirt

They’re all over the place, and depending on where you are it’s either ubiquitous or in very short supply. For those of us who didn’t grow up around construction, this term might be a little mysterious! So, what is fill dirt and what is it used for?

Fill dirt is a class of dirt taken from the subsoil, beneath the topsoil. Typically, it has very little organic matter or nutrients but often contains rocks, sand, shale, and other materials. It is typically used for leveling, filling, and building instead of planting.

Fill dirt is, really, just dirt but compared to the dirt that we walk and plant in it is very different- even deficient!

Because it contains so little biological matter and nutrients that plants need, you’re probably wasting your time if you’re going to try and plant directly in the stuff. What you need to do is put down your filter and then put topsoil on top of that for your actual planting.

Nonetheless, fill dirt is an important resource and one that you need to know how to use properly. Keep reading and I’ll tell you everything you need to know about it.

What Does Fill Dirt Usually Contain?

Now, when you hear the term “fill dirt”, don’t let your imagination tend toward “low quality” or anything like that. It’s not useless; it is just not as clean, rich, and pure as the topsoil in your garden.

In fact, fill dirt is usually a mix of several “components” besides soil alone, including stones and sand, to name a couple.

This varies depending on where it is taken from, of course. The actual soil component can range anywhere from heavy clay to sandy loam.

And speaking of rocks, it’s not uncommon to find larger rocks or stones in your pile of fill dirt, but this doesn’t mean you got gypped, either: they belong in there. And let’s not forget sand, shale, and other materials that are considered “nuisance” or subpar for topsoil use.

If it is indeed topsoil that you needed, you might be thinking that fill dirt doesn’t sound like the rich, fertile soil your plants deserve.

And you’re right: Fill dirt isn’t meant to be nutrient-rich or perfect for planting. Its use is more about providing structure and stability, rather than plant nourishment.

What are Some Common Uses for Fill Dirt?

Fill dirt might not win you any gardening contests on its own, but it’s still incredibly useful in so many applications….

Need to backfill a hole or trench you dug? Call in the fill dirt. Got a piece of land that’s more dirt bike track than a useable parcel? Fill dirt to the rescue, smooth it out!

It’s also a necessity when it comes to supporting foundations and other structures during new construction: it settles far less than topsoil, so once it’s set and packed, you can count on it to stay put and hold up what needs holding up.

Whether you’re building a new home, deck, or shed, or just leveling some rough ground, fill dirt provides the solid base you’ll need.

Fill dirt is also constantly used for erosion control, helping to keep landscapes and structures in place when wind and water tend to carry soil away.

And while fill dirt is a poor choice for growing in, it is still useful as, obviously, subsoil: it serves as a “base layer” for gardening and planting crops, with topsoil spread on top to provide plants with nourishment.

So, while fill dirt is a dirty word when it comes to growing, it’s still a ubiquitous resource for construction, grading, and landscaping.

To sum up, you can use fill dirt for:

  • ✅ fill holes in your backyard
  • ✅ backfill a trench
  • ✅ erosion control
  • ✅ as subsoil

Does Fill Dirt Have Nutrients?

No, not really. Unlike its more coveted cousin, topsoil, which is rich in organic matter and nutrients by definition, fill dirt is truly plain, even barren.

While topsoil gets all the attention with its abundance of organic material, fill dirt rightly, is to be avoided: It has very little to no organic matter, and that means it lacks the necessary nutrients plants need for growth, essentials like nitrogen, phosphorus, and potassium.

So, if you’re thinking of getting a good deal on putting in your new garden or raised beds by using fill dirt as a cheap alternative to topsoil, you definitely want to reconsider.

Can You Grow Anything in Fill Dirt?

If you really, really wanted to, or had to, could you grow something in fill dirt? Maybe, but it is unlikely unless you are talking about a seriously hardy plant.

In its natural state, fill dirt simply isn’t hospitable to most plants. The lack of nutrients we talked about is the chief, and fatal, flaw. No nutrients, no growth. Simple as.

However, that doesn’t mean fill dirt is totally useless for gardening. As mentioned, while you can’t grow plants directly in fill dirt, it can provide an excellent base for your garden.

You can layer nutrient-rich topsoil on top of fill dirt and it provides structure and stability while the topsoil gives your plants the nutrients they need to thrive. So, in a way, fill dirt is still needed for gardening.

Something else to consider is that this type of dirt won’t have a variety of organisms living in it compared to soil that is much closer to the surface. I’m talking about worms, yes, but also things like grubs, beetles, and microorganisms like various kinds of bacteria.

These things are always underfoot, and we seldom think about them, but you’ve got to remember that soil is really an ecosystem unto itself with many different creatures and processes working together, even if they’re working separately, for the benefit of everything else in the ecosystem.

This can have serious implications if you want to plant directly in fill dirt…

Is it Possible to Amend and Improve It for Growing?

Clever homesteaders might already be thinking that they can just tune-up fill dirt to turn it into soil that is more suitable for plant growth. And you’re on to something! It’s possible to do just that, and give your fill dirt a little makeover of sorts.

By adding organic material like compost, aged manure, or leaf mold you can introduce nutrients and also improve the soil structure. You could also consider adding a slow-release fertilizer to provide a steady supply of nutrients to plants over time. All worthwhile endeavors, to be sure.

But do keep in mind: this is not a one-and-done deal. Amending fill dirt is an ongoing and often tedious process that requires regular infusions of organic matter to maintain the nutrient levels and slowly convert it into soil that is amenable to plant- and other life.

You can’t just call it good after a few treatments, especially if your fill dirt is badly deficient. I will tell you more about why in the next section.

Fill Dirt is Still a Poor Choice for Growing After Amendment

Now, before you get too excited about saving a bundle on rich soil by simply turning your fill dirt into a proverbial plant paradise, there’s more you should know. Things that will likely affect your decision! Sadly, even after regular amendment, fill dirt is often still a poor choice for growing plants.

Despite your best efforts, your fill dirt will likely remain prone to compaction. This means it will become so dense that plant roots will struggle to penetrate it normally. This can lead to root binding and other maladies which can impair growth or outright kill your plants.

Plus, fill dirt lacks the beneficial microorganisms and larger critters that help the soil stay loosened up and absorb the nutrients your plants need.

And let’s not forget about its water retention, or rather its lack thereof. Fill dirt does a terrible job of holding onto water to keep plants hydrated, whereas topsoil is “hydrophilic” and stays moist longer, keeping plants cool and watered in kind.

If you are working with fill dirt, even if you water regularly your plants will end up thirsty quicker and more often. Major bummer!

So, while you can certainly try to improve and work with fill dirt alone for planting, think of it like restoring an old junker: it might work and look wonderful after a long, expensive process, but it is going to be a huge pain in your ass the entire time until then.

You’ll always have need of fill dirt for this and that, but when it comes to planting you’re always better off starting with good topsoil for your gardening needs.

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