Compost vs Soil: What's the Difference? - Gardening Channel (2024)

by Matt Gibson

Compost and soil are relatively similar toeach other, and therefore it can sometimes be hard for people to distinguishbetween the two mediums. Adding a layer of compost or a layer of topsoil toyour garden soil mix will help to add nutrients to depleted soils and willimprove the overall quality of your soil. There are many benefits to addingeither medium to your soil.

In this article we will define compost andsoil, respectively. We will also discuss the advantages and disadvantages ofadding either compost, soil, or both to your garden beds. Since there is ahandful of different types of soil, we will explain the difference between eachtype.

We also illustrate the commonalities anddifferences between the two and let you know when it’s best to use each of themto boost the nutrient levels of your soil, as well as to change the compositionof your soil between growing seasons.

What Is Compost?

Compost is a mix of decaying nutrient-richsoil with medium density that is naturally made using oxygen, bacteria, water,and organic materials. Compost combines green matter, such as food products andlawn clippings, with brown matter, such as twigs and dry leaves. Thiscombination then begins to deteriorate in the composting process. The materialsbreak down into a rich soil, which is predominantly used to refresh depletedsoils in the springtime just before planting a new set of crops.

Uses of Compost

There are many ways to use compost in thegarden once it has completed maturing and has become ready to use. You canspread it as mulch, mix it in with your soil to improve quality, water downcompost tea to use as a liquid fertilizer, or spread it directly onto anaerated lawn.

To use compost as mulch, treat the compost thesame way you would any other type of mulch and create a two to three inch layeron the top of your garden beds once or twice per year.

If your soil needs improving, just dig thecompost through your soil down to about four inches deep. You can also speed upthe composting process by adding worms or vermicomposting, or by composting inan insulated bin which is designed to trap in heat, allowing food scraps andother organic materials to break down quickly in the composter.

Compost tea is water that has been soaking incomposted materials. During the soaking, some of the compost’s nutrients,microorganisms, and humates are leached into the liquid. Humates assist plantsin their ability to better use nutrients that are available in the soil andprovide a host of other benefits as well. Adding compost tea to your soilinstead of water will help to boost the nutrient levels in your soil.

Advantages of Using Compost

The advantages of using compost are asfollows:

• Works as a nutrient booster forthe entire soil
• Keeps the natural health of yoursoil at a high level
• Helps for the proper growth ofbeneficial microbes
• Provides the soil with sufficientnutritional elements
• Helps the soil retain moisture
• Promotes proper growth of plants
• Helps the soil fight againstdisease
• Helps to control and limit weeds
• Works to feed soil directly
• Because you can make your owncompost, it is much cheaper and more environmentally friendly than organic ornon-organic fertilizers.

Compost sounds like a winner for multiplereasons, but using compost in your garden also has a few drawbacks.

Disadvantages of Using Compost

The disadvantages of using compost are:

• When using compost, make sure thatnone of your garden plants have soil-borne pathogens
• Compost takes more time to createan effect in the soil than other additives
• Composting can be a verytime-consuming process, taking months to break down completely.
• Making compost requires morephysical labor than digging up a bit of topsoil
• As compost is made from decayingorganic matter, sometimes compost spreads can be kind of smelly.
• Compost takes more space to storeand process.

When to Use Compost

If you are simply looking to improve thequality of the soil, compost is your best friend. Thanks to years of constantconstruction and agriculture in the Southeastern US, our soils are longing foressential nutrients. Incorporating compost into the soil helps to get some ofthe nutrients back into the ground for plants to use for optimal growth.

Also incorporate compost into your soil whenplanting shrubs, adding flower beds, installing sod, or sowing seeds. Youshould mix it into your soil by raking or tilling it in to apply nutrients intoyour topsoil.

When planting shrubs, flower beds, installingsod, or sowing seeds, you should try to incorporate compost into your soil byraking or tilling it in to apply nutrients.

There are organic compost mixes that you canuse just like potting soil with certain plants, however. Soil3 organic compostis one of these all purpose mixes. Whether constructing raised garden beds, orjust filling a few flower pots, you can plant directly into Soil3 organiccompost. It’s a nutritious blend that gives your container plants all the boostthat they’ll need to maintain a healthy growing season.

Different Types of Compost

If you are using pure compost to top-dressyour law, you should strain it so that it will work the best, incorporate intothe soil more quickly, and better blend into the topsoil of your home insteadof just sitting on the top level of your beds.

Thoroughly sieve your garden soil beforeapplying heavier mediums so that the compost can be a top-dress that works itsway through the deep veins, never to be heard from again. The most populartypes of compost are:

CompostedWood Waste – this organic pure compost is made fromwood chippings and cuttings from trees that may have been composted.

CompostedGreen Waste – This is made from garden waste andkitchen food and is commonly made in a compost bin.

CompostedManure – This is raw manure which has been compostedand usually contains some straw particles.

Sterilized Loam Compost – This is a combination of sand, silt and clay that has been treated to insure that there are not any undesirable chemicals or organisms growing in it. Typically, loam has a higher percentage of sand and silt than it does clay.

What Is Soil?

Soil is the top layer of the earth. Soils aremade from various proportions of sand, silt, clay, and small amounts of organicmatter in and on the earth as well as years service past me… The naturalmedium in which to grow plants is indoors. A publication from the EPA saidthere are more than 70,000 different types of soil out there.

Soil formation occurs when many things happento interact over a period of up to 1,000 years. Air, water, decaying plantlife, rock, animal life, and chemicals all interacting, as well as plant rootsand lichens wearing down rocks, creating new soil, and roots and oxygen help toloosen and aerate it.

After several growing seasons using this soil,you will need to amend the soil and add soil to get the nutrient levels back toa suitable level. That is where compost becomes important.

Advantages of Using Soil

Using topsoil to topdress your lawn is ahealthy way to boost the quality of your soil and should be done as often aspossible. Not only will top-dressing make your grass much healthier, but itwill help increase its drought resistance and make your soil less prone toinfestations.

• When you add a layer of topsoil,all the nutrients in this fresh layer will get absorbed into the root systemwhere it will have the most benefit.
• As your garden’s plants feed offthe nutrients in your soil, the nutrients need to be replaced, which you can dowith fertilizer. However, when you add a layer of rich soil to the topsoil, youdo not have to use fertilizer, or can reduce usage, as you are alreadyreplacing .
• Adding layers of organic soil toyour topsoil starts a chain reaction of beneficial events as the soil starts tofully decompose, encouraging the thatch in your lawn or garden to also start todecompose.
• If you have an uneven lawn thenadding topsoil is a wonderful solution, as you can use the added topsoil as anopportunity to even out the surface level of your lawn, while also improvingyour soil.
• Topsoil is great for use when youare creating a new flower bed or raised bed. It’s also perfect for topdressingweak lawn areas. It can be used as a base for improving existing lawns, or forcreating new lawn areas.

Disadvantages of Using Soil

So when is using topsoil not the best idea?

• When growing plants in pots, youaren’t going to have the best results using only topsoil, as it doesn’t reallyprovide enough nutrients for container gardening, unless it is mixed with apotting soil medium.
• Adding topsoil to your garden bedsis fine, as your plants are able to spread out their roots and reach for morenutrients, but in a pot, especially when several plants are planted together inthe same pot, using topsoil isn’t the best choice.
• In the summer, when you areplanting bedding plants into containers to move them indoors, it is a betterchoice to use a potting soil medium, or compost, which will be better suited tothe task, as you need more organic matter, more nutrients, and maybe even aslow-release fertilizer for the job.

Different Types of Soil

There are three different types of topsoil:

Claysoil – Clay soil is composed of tiny particles thathold water well but do not drain sufficiently. If you have a clay heavytopsoil, you should space out waterings as your soil will need ample time todrain. On the plus side, soil that holds water well also holds on to nutrientsfor longer periods, meaning you won’t have to amend as regularly to keepnutrient levels high.

Loamsoil – Loam soil is composed of a mix of sand, clay,silt, and organic materials, and it is the ideal type of soil when it comes tonutrient levels. Loam soil is perfect for adding topsoil to your lawn orgarden, as it is rich in nutrients and organic matter.

Sandysoil – Sandy soil is the opposite of clay soil when itcomes to water and nutrient retention. If you have a sandy soil, you will needto water and fertilize it more regularly.

When amending your soil, balance is key. Ifyou have a soil that isn’t draining well enough, adding sandy soil will improvedrainage. If your soil isn’t holding water or nutrients very well, adding a clay-basedmedium will help to improve retention. If your soil is too sandy or too clayheavy, adding a loamy soil will help to improve its makeup.

Potting soil is also available in manydifferent forms, and it too can be used to amend the soil already present inyour garden beds.

Common Questions and AnswersAbout Compost Versus Soil

Are soil and compost the samething?

Compost and soil are not the same thing,although compost can be added to soil and become part of its makeup. Compost ismade of organic material, while soil also includes elements that are notorganic, such as rock particles or minerals. The word “soil” also tends to beused to describe the top layer of the earth’s crust, a natural material, whilecompost is made by humans. Gardeners mix compost into the naturally occurringsoil in their gardens as a soil amendment to increase the nutrition availablefor their plants.

Can I compost directly in mygarden?

While it’s not the most common technique,composting directly in your garden is possible. This simple approach tocomposting is called the “trench compost method.”

To compost directly in the garden, dig atrench in an unused section of the garden where you’ll be planting soon or inbetween the rows of your plants. Drop your compost materials into the hole,then cover them with soil to fill in the trench. As the compost materialsdecompose, the nutrients they contain will become part of the soil. Wait sixweeks before planting on top of the trench to give the compost time to breakdown.

Trench composting is an easy way to amend your soil with compost. The only drawback to this technique is that it cannot be used in winter if your region gets cold enough for the ground to freeze. For instructions and more information, read our article “Trench Composting: Just Dig a Hole and Forget It!”

Can I plant vegetables incompost?

Most of the time, vegetables can’t be grown incompost alone; the compost must be mixed with soil for vegetable plants to growin it. That’s because compost is a soil amendment that is meant to improve thequality of soil and add to the nutrition it contains. However, you can growplants that don’t need a lot of structural support from their soil in compostalone.

Plants that you can grow in just compost without other soil added include cherry tomatoes, baby carrots, spring onions (also called green onions or scallions) and small herb plants. For success when growing these plants in just compost, you’ll want to make sure the pH level of the compost is between 6.0 and 7.0. If you aren’t sure of your compost’s pH level, you can read our article titled “How to Test pH in Your Soil” to learn how you can find out what your compost’s pH level is.

Can I use compost instead oftopsoil?

It’s possible to use compost instead oftopsoil if you need to, like when topsoil has eroded and must be replaced withcompost. To use your compost as topsoil, make sure to grind the compost down toa fine texture. Getting your compost to a fine consistency helps the compost tomimic topsoil by allowing it to be packed more tightly and making it easier tomix with fertilizer. That said, you don’t want to go overboard and grind yourcompost until the particles are as fine as dust. Shoot for the same texture asregular soil when you’re preparing the compost.

You will also need to add fertilizer to thecompost so you can grow healthy plants in it. Although compost is often thoughtof as a fertilizer, it does not contain enough of certain nutrients that plantsneed to flourish, such as nitrogen, phosphorous, and potassium. When you’rereplacing topsoil with compost, use a layer that’s between six and 12 inchesthick so plants have enough room to develop strong root systems.

Finally, you’ll need to check the pH level of your soil to ensure it meets the needs of the plants you’ll be growing. Check out our guide to testing the pH level of your soil for more information.

Can you add too much compost?

Yes, it’s possible to add too much compost toyour garden soil, and doing so can have negative results for your plants. Toomuch compost means too many nutrients, so once plants have taken in what theyneed to thrive, the excess nutrients (like nitrogen and phosphorus) stay in thesoil. While an excess of nutrients doesn’t sound like something that can causeproblems for your plants, as the excess accumulates over time, the nutrientsthat are healthy in small doses can reach levels that are toxic for yourplants. Limit your compost application to one or two inches on the surface offlower or landscape gardens and three inches on the surface of vegetablegardens.

When there’s too much phosphorus present insoil, that makes it difficult for plants to take in the manganese and iron theyneed, leading to malnutrition that can cause interveinal chlorosis. Too muchphosphorus can also wipe out the population of beneficial mycorrhizal fungi,forcing plants to put energy into expanding the size of their root systemsinstead of using that energy for flowering, fruiting, and growing stronger andhealthier. Having too much of certain nutrients because there’s too much compostin the soil can also make plants grow too quickly. When they grow too quickly,plants miss out on producing the natural pesticides that protect them frominfestation by garden pests and the diseases those pests can carry.

Can you fill a raised bed with justcompost?

Most plants won’t grow well if they’re plantedin just compost without other soil added. (Exceptions include cherry tomatoes,baby carrots, spring onions, and small herb plants.) Ideally, the soil you growplants in should contain no more than five percent of organic matter likecompost. A good rule of thumb to make sure your compost doesn’t exceed thebeneficial level is to limit your application to an inch or two on the surfaceof flower beds or landscape gardens and three inches on the surface ofvegetable gardens.

Can you put dead plants incompost?

Most of the time, dead plant material is anexcellent addition to your compost heap. You should avoid adding plants thathave gone to seed or plants that are affected by disease to compost so theydon’t start growing in the compost pile or spread the disease they are affectedby. Large branches should also be left out of compost, as well as any plantsthat were heavily treated with pesticides or other poisons.

Can you plant grass seed oncompost?

You wouldn’t want to plant grass seed in justcompost without any soil added, but you can use compost to help in the processof planting your grass seed. Simply mix the seeds with compost and apply thismixture on top of the soil where you want to plant the grass seed. Combiningyour seeds with compost like this gives them some weight and prevents the seedsfrom lying exposed on the surface of the soil, making them less likely to beblown away by the wind, carried off by birds or other wildlife, or washed awayby rainfall or irrigation.

Do you need fertilizer if you usecompost?

Although people sometimes think of fertilizerand compost as being in the same category, compost is not a fertilizer and thetwo should be used together. You need fertilizer even if you’re already usingcompost because compost alone doesn’t contain enough of the nutrients yourplants need to flourish, like nitrogen, potassium, and phosphorus.

Does compost go on top of soil?

You can either mix your compost into the soilyou’ll use in the garden or apply the compost on top of the soil—either wayworks. To use compost on top of soil, just spread a layer over the surface asyou would mulch. Use no more than an inch or two on flower beds or forlandscape plants and three inches on the surface of vegetable gardens.

Does compost turn into soil?

Compost is a soil amendment, so it is mixedinto topsoil in the garden and becomes a part of it. Compost is made of rottedorganic material, while soil contains other substances as well, like minerals androck particles. Whereas compost is created by humans, soil is the naturallyoccurring top layer of the earth’s crust. When compost has decomposed, brokendown, and become a part of the soil, it is called “humus.”

How do you mix compost into soil?

You can amend your soil with compost either byadding compost in a layer over the surface of the soil or by combining thecompost and soil and working them in together. To mix compost into your soil,start by layering the compost over the soil’s surface. Use one or two inches ofcompost over flowerbeds and landscape plants or three inches of compost overvegetable gardens. You can stop here if you want to leave the compost on thesurface of the ground like mulch, or to mix it into the soil, till your gardenarea to work your compost into the soil to a depth of six to eight inches. Thisprocess is best completed before you sow seeds or add transplants to the gardenat the beginning of the growing season. Alternatively, you can mix compost intoyour garden soil at the end of the previous growing season.

How long can you keep compost?

It’s best to use compost as soon as you can,but when it’s not possible to use compost quickly, you can store it until thefollowing season. However, compost that is not used by the following seasonshould either be mixed into compost that is almost finished or revitalized byadding more materials to feed the microorganisms compost contains.

How long does it take for compostto turn into soil?

The amount of time it takes for compost to breakdown into soil you can use in your garden varies depending on the size of yourcompost pile, what materials go into the compost, and how the compost istended. For compost to transform into soil can take anywhere from three monthsto two years.

How thick should topsoil be?

Topsoil should be at least six inches deep sothat there is enough room for the root system of your lawn or other plants todevelop.

Is compost enough fertilizer?

While amending your soil with compost does addsome nutrients, compost does not include enough of the nutrients your plantsneed to be healthy (like nitrogen, potassium, and phosphorus). For this reason,you should use fertilizer in conjunction with compost to ensure your plantshave access to the nutrition they require.

Should I mix sand with topsoil?

Mixing sand into your topsoil has severalbenefits for your garden or lawn. Combining your topsoil with sand aerates thesoil, creating small pockets of air throughout the topsoil that make it easyfor the root systems of your plants to reach nutrients, water, and oxygen.

Adding sand to your topsoil also improves thesoil’s overall ability to drain water quickly, preventing oversaturated orcompacted soil. Good drainage is vital for many of the plants you may begrowing in your garden. Incorporating sand in your topsoil loosens the soil upas well, making it less dense and heavy, which makes it easier for roots togrow and expand.

Adding coarse sand to your topsoil can alsoimprove the germination rate of plants that have small seeds. The moresubstantial granules of sand prevent the seeds from falling down through cracksbetween soil particles and getting lost under the surface where they won’t getthe sunlight that’s essential for germination. Make sure that when you add sandto your topsoil, you create a balanced mixture—you don’t want to end up withmore sand than soil.

What is the best ratio of compostto soil?

The best ratio of compost to soil is dependenton the type of garden the soil is intended for. As a general rule, five percentcompost is a good place to start for most types of gardening. This ratioincreases for container gardening (20 to 50 percent), flower gardens (20 percent),and planting new trees or shrubs (10 percent). A guideline that’s easy tofollow is to add one or two inches of compost over the surface of flowergardens or landscape plants and three inches over the surface of vegetablegardens.

What should you not compost?

Materials that should not be composted includethe following:

• Alliums like onions or garlic
• Ashes
• Bread or bread products (likepastries, pasta, or baked goods)
• Cat litter
• Cooking oil, grease, or anythingsaturated in oil or grease
• Cloth
• Dairy products
• Dead animals
• Debris from diseased orinsect-infested plants
• Debris from plants that have beenexposed to insecticide or other chemical treatments
• Debris from plants that have goneto seed
• Debris from weeds or otherinvasive plants
• Diapers or other items soiled withbodily fluids
• Feminine hygiene materials (likepads or tampons)
• Foil
• Large branches or chunks of wood
• Lime
• Manure from cats, dogs, humans, orany sick animal
• Meat scraps (including fat, blood,and bones)
• Paper that is colored, glossy,heavily coated, or has been printed upon
• Peels from citrus fruits
• Poisonous or toxic items of anykind
• Produce labels or stickers
• Raw or cooked rice
• Sawdust
• Synthetic fertilizer
• Synthetic materials or anythingnonbiodegradable (acrylic, plastic, polyester, rubber, and the like)
• Tea or coffee bags (but coffeegrounds or tea leaves that are not in bags are fine to include)
• Walnuts or debris from blackwalnut trees

Where should compost be—in sun orshade?

Compost can be kept either in the sun or in the shade, but the sunnier the spot is where you position your compost, the quicker the materials will decompose into humus. That means if you put your compost pile in a sunny spot, the compost will be finished and ready to use faster than if it were located in the shade.

Want to learn more about compost versus soil?

Backyard Boss covers Compost Vs Topsoil

StackExchange Gardening & Landscaping covers What is the Difference Between Compost and Soil?

Gardens Alive covers What do Compost, Topsoil, Humus, and Composted Soil Really Mean

Green Thumb Planet covers Compost Vs Topsoil

Grow Your Heirlooms covers Soil Vs Compost, What’s the Difference?

Hunker covers What is the Difference Between Compost Potting Soil

Southwest Gardener covers The Dirt On Soil Versus Compost

Topsoil Shop covers Topsoil Vs Compost

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