There’s no shame in being a novice of anything, especially not composting. Composting is a novel thing to do in an age where our planet’s future is in jeopardy.
So, give yourself a pat on the back just for wanting to create healthy, organic soil for your home garden! Give yourself another one for being inquisitive when it comes to what you feed to your plants and another for wanting to help save our planet.
But sometimes diving into the world of composting and gardening uncovers a lot of questions, new terminology, and natural mysteries.
- What the heck is soil, really?
- Is soil dirt?
- What is compost made out of?
- Are all these interchangeable? Is compost soil? Is soil compost?
We’ll look into the answers to all these questions below.
Earth! Soil is what you’ll find on the top layer of earth. It’s basically the top six or ten inches of the earth. But that’s just the quick answer.
Soil is a combination of sand, silt, rock, minerals, gases, plus organic matter and other nutrients. The decomposed organic it contains may be plant material, dead animals, and insects—and these organic parts of the soil alone are considered compost.
But, we’re getting ahead of ourselves.
Soil also includes friendly microbes and fungi that are essential to the soil’s health. These microbes and fungi are typically added to a garden’s soil by compost. Thanks, microbes and fungi!
Organic matter is extremely helpful in maintaining soil moisture. Healthy humus (not the yummy garbanzo bean dip—see below) can hold up to 90 percent of its weight in water! It also helps absorb nutrients for plants to access with their roots. Organic matter is also food for microorganisms and other forms of soil life.
Soil is formed when various aspects of a region’s particular ecosystems interact: water, air, decaying plants and animals, rock, chemicals. The earth’s soil has been formed over a thousand or more years, as plant roots break up rocks, rain and wind erode rocks, worms, and other bugs roots through the particles, and microscopic organisms slowly mix and loosen the materials. The proportion of sand, silt, and clay particles in the soil determines its texture, drainage, and nutrient make-up.
This is why soil is so unique to its region of the earth. Some places have very sandy soil, some have soil with lots of certain minerals. The soil in Kentucky’s Bluegrass region sits atop a massive hunk of limestone, which is rich in calcium and other healthy minerals that help that “blue” grass thrive and supposedly make those racehorses so strong. Pretty cool, right? Soil is smart!
Some regions without lots of human industrial development are home to healthy, vibrant organic soil that doesn’t need amendments to help plants thrive.
In many places, though, due to development and environmental factors, topsoil is thin or nonexistent. In its place has accumulated a cruddy, lifeless soil wanna-be and that might even be filled with microplastics and chemical run-off. Calling this stuff “topsoil” is a stretch.
Soil is the natural medium in which plants grow, but it usually needs some help with that. That’s where compost comes in.
Parts of Soil
As you might’ve guessed, there are a number of different parts of the soil that you use every day. Even though you may not know that you’re relying on the parts of soil, they’re working hard for you!
Humus, with one “m,” is the name for the dark, rich layer of organic material that forms in soil when plant and animal matter decays. Again, this is technically compost. But it’s a kind of compost that nature creates by itself— if we let it.
Out in the “wild,” when plants drop leaves, twigs, and other material to the ground, the plant product piles up, decomposes, and creates humus. The forest creates its own compost, which is technically called humus, as trees and animals decay and return to the earth. Humus lays on top of the soil.
Topsoil is the thicker layer of earth beneath a natural layer of humus. As we mentioned above, it’s full of the good, plant-nourishing stuff like subsoil.
The subsoil is the thicker layer of earth material beneath the topsoil. Like topsoil, it contains a mix of minerals and particles, but it has a much lower percentage of organic matter.
While it’s not incredibly nutrient-rich, subsoil plays a very important part in holding the topsoil in place, and therefore holding plants in place. Big tree roots penetrate into the subsoil to anchor themselves, but most plants’ roots remain on the topsoil.
Soil Is Not…
Dirt! Dirt is mainly ground rock and pebbles. It’s mineral content but has no nutrient content. Whereas soil is moist and crumbly, dirt is dusty and dry.
Compost! Soil is not compost, although compost is part of the soil. We’ll dig into that next.
Unfortunately, human activity is rapidly depleting naturally healthy soil, as commercial farms obliterate the rich top layer to remove weeds and other local flora. This, in addition to applying chemical pesticides and harsh fertilizers, has created dead, dry, and inert earth.
That land-leveling makes sense for huge, industrial farming practices, but this kind of farming has destroyed the very thing nature gave us to grow in. It’s a vicious cycle of destruction.
Add natural disasters due to climate change like long draughts, unprecedented rainfall and floors, and deadly fires, and the planet’s topsoil is being left unviable for life.
But there is hope. Many small- and large-scale farmers are realizing it’s urgent that we replenish our planet’s topsoil and are making their own organic compost to do that.
- Recycled organic waste
- Serves as a soil amendment or “conditioner.”
Compost smells a lot like good soil—earthy, fresh, rich. Not stinky. Yes, even human waste in a composting toilet isn’t odorous. Check this out if you don’t believe me.
Compost and topsoil are not interchangeable. The purpose of compost is to improve topsoil. Compost is not soil, but compost is in soil. (Like that rectangle/square thing…)
Compost improves soil by bulking up its organic matter and improving moisture and nutrient retention. It breaks up heavy clay soils, improving drainage. It improves sandy soils by helping to add moisture. If it sounds pretty amazing, that’s because it is! It’s no accident that compost is nicknamed “black gold” for the value it adds to the soil.
Unlike soil, compost does not (or should not, at least) contain things like sand, silt, and clay. Compost is organic matter and only organic matter.
Compost is a soil amendment, which means it can’t be used alone to grow plants. It needs to be mixed with soil. Compost is just too moist and too full of nutrient assets—planting your garden in straight compost would be like taking a dozen vitamins and chugging two gallons of water.
Chances are that would give you a stomach ache.
Sure, you can buy a bag of compost just like you can buy a bag of topsoil. But what’s the fun in that? Check out our in-depth guide to the 10 Best Composting Methods or The Vermicomposting Guide to find a technique that works for you.
It can be as simple as throwing your kitchen scraps in a barrel in the backyard and mixing it up every few days.
There are lots of things similar to compost; these include things like manure, mulch, and all kinds of organic matter. All of these gardening tools are used for slightly different purposes for a myriad of different reasons.
So, what makes them different? How can you use them along with compost to help your garden flourish?
Manure is NOT compost! Manure can be composted, but it’s never, ever a good idea to use fresh manure in your garden. It needs to be “aged” in order to be safely applied.
Manure is a good source of nitrogen and other nutrients that plants need. These amounts vary depending on the animal’s diet and the amount and type of bedding it has.
Spreading even a little bit of composted manure on your garden can boost soil health greatly.
Composting manure will kill harmful parasites and reduce seeds from weeds. You can compost animal waste yourself through a hot composting method, but your technique must be quite precise. It can take several months for manure to decompose properly and safely,
Composting chicken droppings, though, can be a bit easier to compost, since chickens are little compost-mixing machines themselves. See our guide to Composting with Chickens to learn more.
Consider mulch less of a part of the soil and more like icing on the cake.
Mulch is applied to the top of the soil to cover it. Its main purpose is to discourage weed growth and keep the soil and plant roots warm and moist by providing the soil with a layer of protection from the elements. Just like you would use a winter jacket to stay warm, or a parasol to protect again the sun’s rays to stay untoasted.
Mulch can also improve soil structure as it decomposes over time—which is a good reminder that whatever you put on top of your soil will also eventually go into your soil. If your mulch is contaminated by things like weed seeds, untreated pet waste, and lawn chemicals, those will eventually seep into your soil.
Combined with a soil enriched by compost, mulching also allows worms to aerate your soil by protecting them from weather, birds, and other predators. It’s a hard life for an earthworm—why not give them a little protection? They’ll help rebuild your soil in return.
Commonly, mulches are made out of:
- Wood chips
- Shredded yard waste
Building Healthy Soil
The soil you’ll find when you stick a shovel in your backyard is probably less than ideal—sometimes far less. The good news is that you can rebuild your soil over time, possibly even with compost that you make in your own backyard.
Start with three inches of a high-quality compost (home-made or store-bought) and mix this into the first six or eight inches of soil. Balance is key; plants have the right amount of nutrients and moisture but can be harmed by harsh ingredients like too much nitrogen. Strong soil has about five percent organic material (humus/compost), but you can eye-ball it. No need to get out your measuring spoons.
Focus on the top layer (about 10 inches) of earth, since this topsoil is where your plants will make their roots, sucking up nutrients and moisture to grow. Over time, give your garden lighter, more frequent compost applications to build up the soil.
As the seasons roll by, watch your little plot of this planet prosper from your efforts to regenerate its natural way of supporting the food you eat, the trees that shade you, and shrubs that house the critters that are essential to your ecosystem. Your garden will be tastier than ever.