How to Make Garden Soil Better
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How to make garden soil better is mostly a yearly habit rather than a one-time fix. Oregon State University Extension says that adding organic matter “is the best way to improve nearly all kinds of soils.” Utah State University Extension and Colorado State University Extension agree on the core idea, but they give different rates and warn about different problems. This guide draws on those three extension pages and lays out a routine you can repeat each spring or fall.
Quick answer
- Test the soil before you add compost or manure, because those materials carry their own phosphorus, potassium and salts.
- Spread 1 to 3 inches of composted organic matter over the bed, then work it into the top 6 to 8 inches with minimal passes.
- Repeat the job every year. Garden soils improve over time, and organic matter keeps dropping if you stop adding it.
- Skip sand in clay, work the bed only when the soil is not wet, and compost fresh manure before it goes near a bed.
Start with a soil test
A soil test comes first because amendments are not neutral. Utah State University Extension notes that composts and animal manures are naturally high in phosphorus and potassium, so it advises having the soil tested before you add them. The same page warns that over-applying nutrients, especially nitrogen and phosphorus, can contaminate lakes and streams or leach into groundwater. Utah State offers soil testing through its own analytical laboratory and explains how to collect a sample.
Colorado State University Extension makes a related point about salt. It says that compost which includes manure or biosolids “has a potential for high salt”, so the origin of the material matters as much as the amount you add. Oregon State University Extension adds that organic matter supplies a slow, steady trickle of nutrients and that you can supplement it with fertilizers based on a soil test. The test, in other words, tells you whether the organic matter alone is enough or whether it needs help.
Know the signs that your soil needs help
Oregon State University Extension lists the clues. Soil that dries and cracks in summer, drains slowly, or is hard to dig whether it is wet or dry likely needs amendment. So do shrubs such as rhododendrons that wilt in heat even when they are watered. The page treats these signs as pointing to the same fix: adding organic matter.
Utah State University Extension explains why many soils in dry regions run low. Its page gives an average of about 1.5 percent organic matter along the Wasatch Front, compared with 4 to 5 percent in parts of the country that get more rainfall. If your garden sits in a dry or sandy region, the native organic matter may be low too.
Choose amendments that add organic matter
Oregon State University Extension lists good organic amendments as wood by-products such as sawdust and bark mulch, well-rotted manure, straw from grass or wheat, and compost. The same page gives a warning that matters before you buy anything: “Confirm that any organic materials were not treated with herbicides, which can persist in soil and injure crops.” Ask where a bulk load came from before you spread it on a bed.
Inorganic amendments are a different category. Oregon State says pumice, perlite, vermiculite and sand mainly act as spacers that increase porosity and aeration. Sand alone does not hold water or nutrients well, and it can make silt or clay soils more compacted. If you use sand at all, the page says to pair it with an organic amendment such as sawdust or compost.
Utah State describes mulch and compost as separate tools. Mulch, such as shredded bark or hay, sits on the soil surface to reduce weeds, protect trees and shrubs, reduce evaporation and moderate soil temperature. It is usually not fully decomposed. Compost is decomposed organic matter that no longer looks like the material it came from.
Handle manure with care
Manure adds carbon and nutrients, but timing and source matter. Oregon State University Extension says that “Manure can add valuable carbon and nutrients, but fresh manure can burn roots and should not be applied directly to established beds.” Its advice is to compost manure first. The page suggests mixing it with a nitrogen source such as lawn clippings or vegetable scraps, building a pile roughly 3 feet high and 2 feet across in an aerated, well-drained spot, and turning it about every two weeks.
Utah State adds a warning about meat-eating animals. Its page says to avoid dog, cat or other manure from meat-eating animals, because unless these materials are hot composted, they carry some risk of spreading pathogens to humans. Colorado State University Extension notes that manure-based and biosolid compost can be high in salt, so the application rate is limited unless a soil test on that batch shows a low salt level.
For a pile you can build at home, see our guide to making a compost pile.
How much to add each year
The three pages give different rates, so start with the one that fits your region and then adjust with a soil test. Oregon State University Extension advises spreading 1 to 3 inches of composted organic matter over the bed and working it into the top 6 to 8 inches. Utah State University Extension recommends incorporating 1 to 2 inches each year. It notes that one inch per year prevents a net loss of organic matter, while two inches of low-salt material helps build the soil. Before you order bulk compost, check how much soil a raised bed needs so the volume matches the bed.
Colorado State University Extension gives a table of routine rates that depends on whether the garden is new or established. Every row incorporates the compost into the top 6 to 8 inches.
| Garden type (Colorado State University Extension) | Plant-based or low-salt compost, before incorporation | Manure- or biosolid-based compost, or salt unknown |
|---|---|---|
| One-time application, such as a new lawn or perennial garden | 2 to 3 inches | 1 inch |
| New vegetable and flower gardens, first three years | 2 to 3 inches each year | 1 inch each year |
| Established vegetable and flower gardens, older than three years | 1 to 2 inches each year | 1/2 inch each year |
The Colorado page also states that three cubic yards of compost cover 1,000 square feet about one inch deep. That gives a quick planning check. This is our own arithmetic from that figure, not a measured rate for your soil. A 200-square-foot bed needs 0.6 cubic yards for each inch, so about 1.2 cubic yards for a 2-inch layer.
Work it into the top 6 to 8 inches
Depth matters as much as the amount. Oregon State University Extension says to work organic matter into the top 6 to 8 inches of soil with minimal passes. Colorado State University Extension states the same goal in its own words: “Ideally, cultivate the soil amendment into the top six to eight inches of the soil.” The Colorado page adds that on compacted or clayey soils, anything shallower can lead to a shallow root system, with reduced plant growth, lower vigor and lower stress tolerance.
Tilling is a tool, not a requirement. Oregon State says one or two passes are usually enough to mix amendments into the upper soil. It warns that too much tilling can create a dense layer that impedes roots and drainage. Utah State lists rotary tillers, double digging and surface spreading as ways to incorporate organic matter.
Wait for soil that is not wet
Timing matters too. Utah State University Extension says organic matter can go in during spring or fall, but only when the soil is not wet. Its page explains that tilling wet soil creates compaction and a hard pan, especially in clay soils. If a bed is soggy, the advice is to wait for it to dry before you work the amendment in.
Watch for nitrogen tie-up with coarse material
Coarse materials need care. Utah State University Extension says that adding materials that are not fully decomposed, such as leaves, sawdust, wood shavings or straw, often ties up soil nitrogen. Oregon State University Extension advises keeping synthetic nitrogen away from tender roots at planting, then adding soluble nutrients later and watering them in.
Mulch and cover crops keep building soil
Oregon State University Extension suggests mulching after planting to hold moisture and keep building soil. For Western Oregon, it recommends a winter cover crop, with crimson clover as an example, as a low-effort way to build soil.
Utah State University Extension treats cover crops as an alternative way to increase organic matter. Its page notes that legumes can supply nitrogen, and that cover crops do not raise soil salinity the way some manures and composts can. Colorado State University Extension takes a more cautious view for its own climate. Because Colorado vegetable gardens use the whole growing season for production, the page says a green manure is less practical there.
Choose compost you can trust
Where the material comes from matters. Oregon State University Extension says that compost and soil mix products sometimes contain herbicide residue, which can damage certain vegetable, fruit and flower crops. Before you buy a bulk load, it suggests asking the vendor how they handle that risk. Utah State University Extension notes that compost is sold through garden centers, landfills and specialist companies.
Mistakes to avoid
- Expecting one season to fix the soil. Utah State University Extension says that garden soils improve over time, so plan on yearly additions.
- Mixing sand into clay. The Utah State page says to avoid amending clay with sand, and Oregon State says sand alone does not hold water or nutrients well.
- Tilling too hard or in wet soil. Oregon State warns about over-tilling, and Utah State warns that tilling wet soil creates compaction and a hard pan in clay soils.
- Spreading fresh manure on an established bed. Oregon State says fresh manure can burn roots, so compost it first.
- Adding compost or manure without a test. Utah State says to test before adding composts and animal manures, and Colorado State says salt in manure-based compost can limit the rate.
- Assuming all compost is the same. Oregon State warns about herbicide residue, and Colorado State warns that many commercial products carry salt.
A simple yearly routine
Start in spring or fall, when the soil is not wet. Test the soil first, and let the results guide any extra nutrients. Spread compost at the rate that fits your region and garden type. Use the Colorado table or the Oregon range of 1 to 3 inches as a planning guide. Work the material into the top 6 to 8 inches with one or two passes instead of repeated tilling.
After planting, mulch to hold moisture and keep building the soil. Between crops, consider a cover crop where your local climate allows it. Utah State notes that its garden soils constantly lose organic matter, which is why the annual addition matters. Repeat the routine each year.
How we chose
This guide draws on three university extension pages: Oregon State University Extension, Utah State University Extension and Colorado State University Extension. We opened each page on 2026-10-23 and kept only statements that the page makes itself. Where the pages give different rates, we show the differences rather than picking one silently. We left out retail, supply, news and blog pages, which add no guidance the extension pages lack. The one calculation is our own arithmetic from a Colorado figure, and it is labeled.
What we could not verify
We could not confirm one rate that fits every garden. Each page is written for its own climate and soils, so the numbers do not transfer neatly from Oregon to Utah or Colorado.
What the sources do not say
The sources do not say how much organic matter your soil holds now, and none of the three pages describes a home test for it. The Colorado page states the broad goal of raising organic content to 3 to 5 percent over a period of years, but the pages do not give a target that applies to every garden. They also do not describe how long it takes a specific soil type to reach that level. The Oregon news release on the same topic repeats the extension article, so it adds no new facts. None of these pages recommends a product, and this guide does not either.
Frequently asked questions
How often should I add compost to garden soil?
Most of the pages call for a yearly addition. Utah State University Extension suggests 1 to 2 inches of organic matter each year. Colorado State University Extension’s table gives 1 to 2 inches of plant-based compost each year for established vegetable gardens older than three years. Oregon State University Extension describes a 1 to 3 inch layer. Start with the range for your garden type and adjust after a soil test.
Do I need to test my soil before adding compost?
Utah State University Extension says yes for composts and animal manures, because these are naturally high in phosphorus and potassium. Colorado State University Extension adds that compost made with manure or biosolids can be high in salt. A soil test helps you decide how much to add and whether the bed needs fertilizer on top.
How deep should I work compost into the soil?
The pages agree on the top 6 to 8 inches. Colorado State University Extension says to cultivate the amendment into that depth, and Oregon State University Extension says to work it into the same depth with minimal passes. Avoid working the bed when the soil is wet.
Is sand a good way to loosen heavy clay soil?
Utah State University Extension says to avoid amending clay with sand. Oregon State University Extension says sand alone does not hold water or nutrients well and can make silt or clay more compacted. Both pages point to organic matter as the better choice.
Can I add fresh manure to a vegetable bed?
Not onto an established bed. Oregon State University Extension says fresh manure can burn roots, so compost it first. Utah State University Extension also says to avoid manure from meat-eating animals unless it is hot composted.
How long does it take to see results?
Expect several seasons rather than one. Utah State University Extension says garden soils improve over time, and it describes annual additions as the way to build soil gradually and sustainably. Oregon State University Extension describes organic matter as a slow, steady trickle of nutrients.
Bottom line
Test the soil, add organic matter at a rate that fits your region each year, work it into the top 6 to 8 inches when the soil is not wet, and avoid over-tilling.
Sources
- https://extension.oregonstate.edu/news/add-organic-matter-improve-garden-soils (opened 2026-10-23)
- https://extension.usu.edu/yardandgarden/research/preparing-and-improving-garden-soil.php (opened 2026-10-23)
- https://extension.colostate.edu/resource/vegetable-gardens-soil-management-and-fertilization/ (opened 2026-10-23)
