Compost vs. Topsoil: What Each One Is and How to Buy Them

What each one is, in plain terms

Oregon State Extension defines compost as partially broken-down organic material. Good compost looks like dark topsoil, has a light, crumbly structure and smells earthy, like forest soil ¹.

It carries almost no sand, silt or clay of its own. Oregon State says compost lacks the mineral part of earth soil and planting mixes ¹.

Topsoil is the mineral soil from the upper layer of the ground.

New Hampshire Extension notes that sellers also call it loam, and that the state has no legal definition of topsoil and no rules governing its sale.

The soil can come from farmland, cleared forest or old fields ³. Maryland Extension says the same: no quality standards, not a regulated product ⁴.

The two do different jobs. Compost feeds the organic matter side of a soil. Topsoil supplies the mineral body that roots grow in. The percent of organic matter in a bed is a result of both, and it is not a property of one bag.

The difference, side by side

How they work together in a bed

Think of topsoil as the body and compost as the sponge and food.

Maryland suggests a blend of compost and purchased topsoil at 1:2 or 1:1 for raised beds with poor or compacted native soil, and says the bed should reach 25% to 50% organic matter by volume, or 5% to 15% by weight, as a lab measures it ⁵.

Oregon State says to add about one-third compost by volume to a landscape bed ¹.

Mixing beats layering. Oregon State says amendments work best worked into the existing soil. A heavily amended planting hole acts like a large pot and limits root spread.

Layering on the surface is slower to raise organic matter ². UNH also says to mix topsoil and organic matter into the top few inches of existing soil rather than spreading it on top ³.

Why not all compost? Oregon State warns that overapplying compost may reduce water quality, because extra nutrients can leach into surface and ground water, and plants can show fertilizer-burn-like injury ¹. See soil structure for how the crumbs and pores form once the two are mixed.

Example: reading two supplier sheets against the targets

Both sheets are invented to show how to read them. The target ranges are Oregon State's and UNH's ¹³².

Passing the numbers is not a guarantee. UNH says it is impossible to judge topsoil quality just by looking at a pile ³, so smell it, ask where it came from and test a sample. Send it to a lab as described in soil testing for lawns and gardens.

Where you meet the choice: bulk yards, bags and bids

At a bulk yard. Both are sold by the cubic yard. Maryland says to ask for soil test results, the soil's origin and how it is mixed and stored ⁴. The mulch calculator converts bed area and depth into cubic yards for any loose material.

In a bag. Bagged products may be called topsoil, garden soil or organic soil. UNH describes bagged topsoil as sometimes limed or fertilized. Check the ingredients ³⁴.

On a bid. Look for the product, the depth and whether it is worked in. A bid that says "topsoil and compost" should say how much of each. The landscaping estimates guide shows how to compare lines.

On a service page. Bed building sits under planting and garden beds, and lawn repair under lawn renovation.

What each one gives you, and what it costs you

Where the guidance disagrees or runs out

The sources do not agree on every number. Oregon State's table lists organic matter of 30% or less for finished compost, while Penn State's turf article lists greater than 30% ¹⁶. They are measuring for different uses. Ask the supplier which method and which use the test sheet follows.

Our topsoil facts come from New Hampshire and Maryland. Other states may define or regulate topsoil differently, and we did not check them. A city or county may also set rules for fill brought onto a site. Ask local officials.

We found no sourced "right" ratio for a lawn or a shrub bed that fits every soil. Maryland's 1:2 or 1:1 is for raised beds with poor or compacted native soil ⁵.

For an existing bed, the better answer often is to amend the soil you have, as Oregon State says, and bring in topsoil only where it helps most ².

What drives the price, and how long each lasts

We do not publish prices. Bulk price depends on the product, the haul distance, the volume, screening and whether the compost is certified or tested. Delivery and spreading labor often matter as much as the material. See the cost hub for what shapes a bid.

Compost does not last. Oregon State says about half of composted organic matter is lost in the first 1 to 2 years after application ², and beds with compost settle as it decomposes, so you may need to refill ¹.

Maryland says vegetable and flower beds need organic matter replaced each year ⁴.

Topsoil is mineral, so it does not decay the same way. It can erode or settle, and its organic matter will fall without additions. We give no lifespan for either product.

How to choose and buy, in order

A homeowner can do this alone for a small bed. For large fill, a landscaper handles the haul and spreading.

1. Test your own soil first. Know your pH, texture and organic matter. See what you need before buying either product.
2. Decide the job. Raising organic matter needs compost. Adding depth or filling a raised bed needs topsoil plus compost.
3. Ask the supplier for facts. Maryland says to ask for test results, the soil's origin, and mixing and storage details ⁴. Oregon State says to ask whether the supplier regularly tests the compost and to request recent results ².
4. Inspect before you accept. Topsoil should be dark and crumbly with an earthy smell; avoid very sandy or clayey soil, foul odors, or gray mottling ⁴. Compost should pass a 3/8-inch screen and have no ammonia or sulfur odor ¹.
5. Check for herbicide residue in vegetable beds by germinating several seed types in a sample, as UNH suggests ³.
6. Mix, do not layer. Work both into the top few inches of existing soil ³.
7. Retest a year later. Maryland suggests testing again about a year after, once the bed components have mixed ⁵.

Keeping the bed healthy after you fill it

Upkeep tasks are listed here without fixed dates. The timing depends on your climate and what you grow.

• Top up compost lightly each year. Maryland says 1 inch a year can maintain productivity ⁴; Oregon State says one-quarter to 1 inch for existing vegetable beds ¹.
• Refill settled raised beds. Oregon State says beds settle as compost decomposes ¹.
• Water in high-salt compost right away on surface use, especially in hot weather, per Penn State ⁶.
• Keep a record of the product, depth and date so you can compare soil tests over the years.
• Do not stack more on top. Oregon State warns that overapplication can send nutrients into water ¹.

Warning signs of a bad product, and when to ask an expert

• Ammonia, sulfur or chemical smell. Oregon State says a foul, ammonia or sulfur odor means composting is not finished ¹; UNH says to avoid chemical or off-odors in topsoil ³.
• Twisted, cupped leaves on tomatoes, beans or peas. Oregon State says growth-regulator herbicide residue can distort broadleaf plants ¹. Maryland names aminopyralid and clopyralid as contaminants found in some manure and commercial compost ⁴.
• Burned seedlings or slow germination. Salts can harm seeds, transplants and sensitive plants ¹.
• Rocks, roots and trash in the pile. UNH says unscreened soil can be full of rocks and roots ³.
• A bed that smells or crusts after heavy compost. Take a sample to your county Extension office.

Rules and standards that apply

Topsoil. New Hampshire has no legal definition of topsoil and no regulations governing its sale ³. Maryland says there are no quality standards for topsoil and it is not a regulated product there ⁴. Other states may differ.

Compost. Maryland says many commercial composts follow U.S. Composting Council guidelines and are regularly tested ⁴. These are voluntary industry programs, not state law, though states may have separate compost facility rules. Oregon State's metals target is that metals meet state and federal standards ¹.

Manure and biosolids. Maryland says manure counts as fully composted when a static, aerated pile reaches at least 131 degrees Fahrenheit for three days in a row, and treats local manure as uncomposted unless verified. EPA Class A Exceptional Quality biosolids are allowed around garden plants ⁴.

Local rules. Cities and HOAs may limit fill, grade changes or runoff. Our soil drainage research covers water behavior.

Compost and topsoil compared with the terms near them

Common compost and topsoil myths

Myth Compost and topsoil are the same thing.

Reality Compost is partially broken-down organic material; topsoil is mineral soil. Oregon State says compost lacks the mineral part ¹³.

Myth Pure compost makes the best raised bed.

Reality Oregon State says not to fill raised beds with compost alone ¹. Maryland suggests compost and topsoil at 1:2 or 1:1 ⁵.

Myth Bagged "organic soil" is topsoil.

Reality Maryland says it typically contains no mineral topsoil ⁴.

Myth Good topsoil is regulated, so the label can be trusted.

Reality Neither New Hampshire nor Maryland regulates topsoil sales ³⁴. Test a sample.

Myth Dark color means good quality.

Reality UNH says it is impossible to judge topsoil quality just by looking at a pile ³.

Myth Layering topsoil over compacted ground fixes it.

Reality Oregon State says the better route is to amend the existing soil with organic matter ².

The local variable: state rules and your native soil

Which one you need, and your next step

Buy compost if your soil is mineral-rich but low in organic matter. Buy topsoil if you lack depth, are building a raised bed or are filling a low spot. Buy both, mixed, for most new beds.

Your next step is a soil test on your existing soil, then a call to the supplier with the questions above. Ask for a sample before the truck comes.

If you want a contractor to haul and spread it, read choosing a landscaping company and ask each bid to list the product, the depth and the mix ratio.

Related terms

Soil Amendments

Soil amendments are materials mixed into or applied to topsoil to change its properties and improve plant growth, such as compost for structure, lime to raise pH and sulfur to lower it.

Landscape Bed Preparation

Landscape bed preparation is the work done to a patch of ground before planting: clearing grass and weeds, correcting drainage, loosening compacted soil, testing it and mixing in lime, fertilizer or organic matter only as the results call for.

Yard Waste Composting

Yard waste composting is the controlled breakdown of leaves, grass clippings, plant trimmings and similar garden debris by microbes into dark, crumbly compost that can be worked into soil.

Soil Compaction

Soil compaction is the squeezing of soil particles together, which shrinks the number and size of the pores between them, so less air and water can enter and roots meet more resistance.

Soil Texture

Soil texture is the weight share of sand, silt and clay particles in the part of a soil finer than 2 millimeters, and USDA sorts every mix into one of twelve texture classes, such as sandy loam, loam or clay.

Mulch Types

Mulch types are the materials spread over soil to protect it, and extension sources sort them into four families: living, organic, inorganic and synthetic.

Also referenced from: Landscape Bed Preparation, Lawn Topdressing, Soil Amendments