Soils and Composting: Soil Improvement

Soils and Composting | Soil Testing | Soil Type | Soil Improvement | Composting


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In simple terms, gardeners may think of soil improvement as making soil favorable for plant growth. Some soil qualities gardeners seek to achieve in a soil include: soil workability, proper drainage and water holding capacity, and adequate nutrient holding capacity and availability.

Because soil physical and chemical properties change over time, so may your methods for making soil improvements. Similarly, the kind of plants you grow and how you grow them may also affect your soil improvement practices. When applying soil amendments, take a soil test to make sure you are applying the correct amount.


This soil was brought in to create raised beds. (Photo credit: Karen Jeannette)

When additional soil is needed for raised beds or other garden needs, many homeowners look to purchase topsoil. Purchasing topsoil can be confusing because the term “topsoil” is often misunderstood. Read the following article, which defines topsoil, what to look for in a topsoil, and which amendments may be necessary to add to new topsoil to make it ready for garden or landscape uses.

  • Purchasing Topsoil (Home and Garden Education Center, University of Connecticut Cooperative Extension)



Organic Matter

Benefits of soil organic matter include improvement of soil structure, infiltration, drainage, water and nutrient holding capacity, and soil fertility, all benefits that promote a favorable rooting environment for plants. Soil organic matter also serves as a source of food and energy for a myriad of beneficial microorganisms. The following article discusses organic matter, how it is formed, sources of organic matter to improve soils, and carbon-nitrogen ratio.



Derived from natural or synthetic materials, fertilizer contains plant essential elements aimed at improving soil to promote plant growth. Improper use of fertilizers can cause environmental harm and damage or death to plants.

An assortment of fertilizers and soil amendments on a store shelf.

There are many types of fertilizers. Learn what these fertilizer terms mean: organic, inorganic, composts, chemicals, slow release, and manure.

Application Amount

Your best bet for applying the right amount of fertilizer is to have your soil tested. Soil test reports will recommend a particular grade of fertilizer and amount to use that most closely matches your soil conditions. If a soil test is not taken, some extension documents recommend certain grade fertilizers for specific purposes. In these cases, use the recommendation for fertilizer grade in the document and apply it according to the directions on the fertilizer label.

Follow these next steps for further information on applying the right amount of fertilizer. Note: Follow the directions on the label for all fertilizer products.

1.    Fertilizer Grade: Understand what the fertilizer grade or analysis on the fertilizer bag means.


  • Inorganic Fertilizers (North Carolina Cooperative Extension), a quick lesson showing where to find the fertilizer grade on a typical bag of inorganic fertilizer and how that information is applicable to fertilizing.
  • Fertilizer Grade [Pg. 14-15] (University of Minnesota Extension), a one-page article that explains fertilizer grade; the percent nutrient composition also is given for a large variety of inorganic and organic fertilizers.


2.    Fertilizer Calculations: Calculate the amount of fertilizer needed based on the soil test and the fertilizer grade you will be using.


  • Calculating Fertilizer Rates from Soil Test Recommendations [Pg. 16-19] (University of Minnesota Extension) Many soil test reports come with recommendations for a particular fertilizer grade, which is usually assumed to be inorganic. However, some gardeners prefer to use organic fertilizers.



Application Methods

Banding, broadcasting, top-dressing, side-dressing, and foliar feeding are all terms that refer to different ways of applying fertilizer.


-Note: Always follow the application methods provided on the fertilizer label.

Soil pH

Soil pH is often considered the master variable because it affects the solubility of all elements, including the nutrient elements required by plants. In general, plant essential nutrients are most available around the slightly acidic to near neutral soil pH values of 6.0 to 6.8. However, there are some exceptions. Iron, which is required in relatively high amounts by ericaceous plants such as rhododendrons and blueberries, is more available at lower soil pH levels. Also, both high and low soil pH levels decrease the availability of phosphorus.


  • Nutrient Availability (Michigan State University Extension), a helpful illustration depicting which nutrients are most readily available in the soil at a particular pH.

Modifying Soil pH

pH test in a soils laboratory. Accurate results provide helpful recommendations. (Photo credit: Peter Bierman)

It is often necessary to modify the pH of a soil. In general, soils east of the Mississippi tend to be acidic and those west of the river, alkaline. Many gardeners prefer to grow nonnative species like turf grasses, flowers, and vegetables that require a soil pH different from that naturally occurring on their site. An undesirable soil pH can limit plant growth by affecting nutrient availability, plant physiological functions, and soil microbe activity.

Typically, ground or pelletized limestone is used to raise soil pH while sulfur or sulfur compounds are used to lower it. How much to apply depends on your soil’s present pH, the desired pH change, and the amount of clay and organic matter present in the soil. Contrary to popular opinion, soils can have too much limestone or sulfur applied to them. To determine how much, if any, of these amendments to apply, test your soil first. If a soil test indicates your soil pH is not in the optimal range for growing plants, pH modification may be necessary.

For more information on soil pH modification, see:

  • Soil pH Modification. Learn how soil pH affects nutrient availability to plants and how to raise and lower soil pH.

Soil-Related Problems

Discovering soil-related problems can be challenging, especially when plant symptoms are similar to those of insect, disease, or other abiotic causes. Fortunately, for soil-related problems such as nutrient disorders, soluble salts, and lead contamination, a soil test with recommendations can help point toward or away from the cause in question. As with any diagnostic effort, it’s helpful to have a good knowledge base of possible plant problems, symptoms, and their management. See the following resources on how to identify problems and minimize their negative effects on plants or people.

Nutrient Disorders

An example of nutrient deficiency: Iron chlorosis on pin oak. (Photo credit: Joseph O’Brien, USDA Forest Service,

Nutrient disorders can affect the look or health of plants by disrupting internal plant mechanisms that cause the plant to function properly. Nutrient disorders may be noticed as nutrient toxicity, when too much of a nutrient is available, or as nutrient deficiency, when not enough of a nutrient is available to the plant. Both nutrient toxicities or deficiencies can lead to problems in how the plant functions and grows. This is one reason why taking soil tests before planting is strongly recommended. Taking a soil test and then appropriately managing or improving the soil in accordance with soil test recommendations and plant needs is analogous to building a home with a sturdy foundation. If the soil has the right balance of nutrients, air, water, minerals, and organic matter, the plant will have access to the nutrients it needs to function and grow properly. If soil is not managed properly, plants are likely to struggle for nutrition and resources, making them function poorly as a direct result of a nutrient disorder or indirectly by weakening the plants defenses, making it susceptible to other problems.

Detecting and Diagnosing Guides and Keys

Soluble Salts

High-soluble salts may be present in soil as a result of overfertilization, use of de-icing salts, irrigation waters, or mineral weathering. Learn how to correct soluble salt problems and identify symptom of soluble salt injury.


Soil Contaminants

While the EPA lists a number of common soil contaminants, most of which are a concern near superfund sites (U.S., EPA). One contaminant that is more prominent in home yards or gardens than many other contaminants is lead. The presence of lead in soil can be tested by a specific lead soil test, available through most university or private laboratories. Learn more about lead in the garden in the following article.

Soil Drainage

Both texture and structure influence the drainage capacity of a soil. Adequate soil drainage enables a plant to access the air, water, and nutrients it needs to survive and flourish. Poor soil drainage can inhibit a plant’s access to air, water, and nutrients, causing stress, and sometimes, decline or death.

How can you determine if you need to modify soil drainage? What can you do to modify soil drainage?


  •  Soil Drainage (Colorado State University Extension) a look at water movement, testing for drainage, and dealing with poor drainage.