Skip to main content

NC State Extension

Answers to Frequently Asked Questions – SOILS

en Español / em Português

El inglés es el idioma de control de esta página. En la medida en que haya algún conflicto entre la traducción al inglés y la traducción, el inglés prevalece.

Al hacer clic en el enlace de traducción se activa un servicio de traducción gratuito para convertir la página al español. Al igual que con cualquier traducción por Internet, la conversión no es sensible al contexto y puede que no traduzca el texto en su significado original. NC State Extension no garantiza la exactitud del texto traducido. Por favor, tenga en cuenta que algunas aplicaciones y/o servicios pueden no funcionar como se espera cuando se traducen.


Inglês é o idioma de controle desta página. Na medida que haja algum conflito entre o texto original em Inglês e a tradução, o Inglês prevalece.

Ao clicar no link de tradução, um serviço gratuito de tradução será ativado para converter a página para o Português. Como em qualquer tradução pela internet, a conversão não é sensivel ao contexto e pode não ocorrer a tradução para o significado orginal. O serviço de Extensão da Carolina do Norte (NC State Extension) não garante a exatidão do texto traduzido. Por favor, observe que algumas funções ou serviços podem não funcionar como esperado após a tradução.


English is the controlling language of this page. To the extent there is any conflict between the English text and the translation, English controls.

Clicking on the translation link activates a free translation service to convert the page to Spanish. As with any Internet translation, the conversion is not context-sensitive and may not translate the text to its original meaning. NC State Extension does not guarantee the accuracy of the translated text. Please note that some applications and/or services may not function as expected when translated.

Collapse ▲

Do I have to get a soil test report or can you just tell me how much fertilizer to add?

A soil test is the only accurate way to determine the amount of fertilizer needed for each individual yard. A soil test is a process by which nutrients are chemically removed from the soil and measured for their “plant available content” within the sample. The quantity of nutrients extracted is used to determine the type and amount of fertilizer to be recommended. The pH and acidity of the soil sample is also measured and used to determine if lime is needed and how much. Soil testing is provided by the NCDA&CS. There is a small fee for each soil sample submitted to the NCDA&CS during December through March, which is the peak season for soil testing in North Carolina. There is no fee for soil samples submitted to the NCDA&CS during the rest of the year (April through November). Samples must be mailed in to the NCDA&CS and boxes are available at their main office, 4300 Reedy Creek Road, Raleigh, NC, or at any N.C. Cooperative Extension center. More information and forms are available on the NCDA&CS website.

How often should soil be tested?

If a soil test report indicates the pH and nutrient levels are in the range needed for plants to be grown, you may not need to sample every year. As a general rule, sandy-textured soils should be tested every two to three years and clay soils every three to four years. However, if nutrient or pH levels are excessively high or low, you should submit a sample every year to determine how much improvement has been achieved and what additional amendments should be made. In addition, if problems occur during the growing season, collect a sample and have it analyzed.

Can I add Epsom salts to my plants?

Epsom salt (magnesium sulfate) can sometimes be beneficial, especially in sandy soils that may be low in sulfur or magnesium. However, the best recourse is to rely upon a soil test and make adjustments to the soil pH and nutrient content based on the soil test report’s lime and fertilizer recommendations.

Why are my (azalea, blueberries, maple, rhododendron) leaves yellow?

Ruling out water issues, the likely culprit is pH. Azaleas, blueberries, maples, and rhododendrons are acid-loving plants requiring a pH of 4.5–6.0 to thrive. Knowing your soil pH will help you select plants that will thrive in your soil. Altering the pH of a soil is difficult, but can be done in small areas.

My shrubs/trees are wilting, the leaves are brown on the edges, and are falling off. What is causing this?

This could be the result of salt injury due to improper application of fertilizer. High salts decrease a plant’s ability to extract water from the soil, and salts can move through the plant’s vascular system to the leaves where the water evaporates and concentrates the salt to toxic levels. Plants may recover from salt/fertilizer injury if high levels of salts are reduced through repeated, deep irrigation. The best defense against this problem is to obtain a soil test and follow the fertilizer recommendations. Avoid the use of high salt fertilizers such as sodium nitrate; use slow release fertilizers and apply correctly. Azaleas and blueberries are very susceptible to salt/fertilizer injury.

My soil is very heavy clay. What can I do?

  • There are several ways you can manage your clay soil.
  • The easiest thing you can do is select plants that perform well in clay soil. Water moves slowly into clay soil so be sure to irrigate slowly. A soaker hose is a good option.
  • Clay soil compacts very easily when wet so keep foot traffic and vehicles away from your garden beds.
  • Adding organic matter like compost or pine bark to the soil is another option. Add a few inches of organic matter to the top of the soil. This will need to be repeated for several years to see results.
  • Build a raised bed on top of the clay soil and bring in soil from a reputable source. Loosen the clay layer in the existing soil before adding new soil to the raised bed so water can adequately drain.

The soil in my lawn is compacted; what can I do to resolve this?

Foot traffic, mowing, recent home construction, and even rainfall can contribute to soil compaction, which can be especially problematic in clay soils. Turf grass roots need air and water to grow. Core aeration is the removal of small cores from the top few inches of soil to allow air, water, and nutrients to enter the root zone of your turf. The result is reduced water runoff and enhanced water and nutrient uptake, gas uptake, thatch breakdown, and heat and drought tolerance of your turf.

The best time to perform core aeration is when grass is actively growing. That means late spring or early summer for warm-season grasses and fall for cool-season grasses. The soil should be moist, but not wet. Be sure to mark sprinkler heads, shallow lines from the sprinkler, and underground utility, cable, and septic lines to prevent damage. Soil cores should be left on the lawn; they will work their way back into the soil within two to four weeks. Lawns may be fertilized, seeded, or top dressed with a soil amendment immediately after coring, although ensure the timing of fertilization corresponds with the recommendations on the maintenance calendar for your turf. Lawns can be aerated once a year, especially under heavy-use conditions and with heavy clay soils. Note that spike aeration is not recommended, as this method of aeration only further compacts the soil.

More Information on Soils