A pH soil test will tell you whether your soil is within the optimum range or whether it will need to be treated to adjust the pH level. Although the optimum range is 5.5 to 7.0 some plants will grow in a more acid soil and some at a more alkaline level.

PH is not an indication of fertility, but it does affect the availability of fertilizer nutrients. The soil may contain adequate nutrients yet plant health may be limited by an unfavorable pH level. On the other hand, builder’s sand, which is devoid of nutrients, may have optimum pH for plant growth.

To correct the pH of or “sweeten” an acid soil (5.5 to 0.0) use lime or dolomite. Lime contains mainly calcium carbonate and dolomite contains both calcium carbonate and magnesium carbonate. Ground limestone and dolomite are less likely to burn plant roots than hydrated lime and is therefore recommended for home use. The greater the amount of organic matter or clay in a soil, the more lime or dolomite required to change a pH level. The best results will be achieved if you incorporate the lime uniformly at least six inches into the soil.

If soil is too alkaline you should determine if it is due to a soil characteristic or lime application. It is very difficult, if not impossible, to change appreciably the pH of naturally alkaline soils by using sulfur, ammonium sulfate, or similar acid forming materials. If this high pH is due to applied lime or dolomite, acid forming materials like sulfur or ammonium sulfate can be applied. To decrease the soil pH use superfine dusting or water soluble sulfur. Repeat applications of sulfur should not be made more often than once every two months because soil sulfur oxidizes and mixes with water to form a strong acid that can burn the plant roots — so use it with caution. It takes approximately 1/3 the amount of sulfur to decrease the pH one unit as it does limestone to raise soil pH one unit. Our soil on Marco Island is mostly alkaline due to the high sand and shell content. Using sulfur coated fertilizers is a helpful practice. These coated fertilizers are the slow release kind which is a more environmentally friendly way to fertilize and it slowly adds some much needed sulfur to you landscape.

Desirable soil ph for optimum crop production pH range

The desirable pH range for optimum plant growth varies among crops. While some crops grow best in the 6.0 to 7.0 range, others grow well under slightly acidic conditions. Soil properties that influence the need for and response to lime vary by region. A knowledge of the soil and the crop is important in managing soil pH for the best crop performance.

Soils become acidic when basic elements such as calcium, magnesium, sodium and potassium held by soil colloids are replaced by hydrogen ions. Soils formed under conditions of high annual rainfall are more acidic than are soils formed under more arid conditions. Thus, most southeastern soils are inherently more acidic than soils of the Midwest and far West.

Soils formed under low rainfall conditions tend to be basic with soil pH readings around 7.0. Intensive farming over a number of years with nitrogen fertilizers or manures can result in soil acidification. In the wheat-growing regions of Kansas and Oklahoma, for example, which have soil pH of 5.0 and below, aluminum toxicity in wheat and good response to liming have been documented in recent years.

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What pH do some common plants prefer?

Whilst most plants prefer a neutral environment, there are exceptions. Here is a list of the exact pH preferences for some common plants, including fruits and vegetables. A guide like this may be included with many of the pH meters available.

Plants that like very acidic conditions (5.0-5.8 pH)

5.0-5.8 is considered very acidic for soil conditions. Plants that prefer this include:

  • Azalea
  • Heather
  • Hydrangea
  • Strawberry

Plants that like moderately acidic conditions (5.5-6.8 pH)

Moderately acidic levels are from 5.5-6.8 and some plants which prefer these conditions include:

  • Camellia
  • Carrot
  • Fuchsia
  • Rose

Plants that like slightly acidic conditions (6.0-6.8)

Plants that prefer the conditions just below neutral at between 6.0-6.8 include:

  • Broccoli
  • Lettuce
  • Pansy
  • Peony

Plants that prefer alkaline conditions (7.0-8.0 pH)

Soil conditions do not venture far into the alkaline side of the pH scale, but plants which prefer conditions just above neutral at 7.0-8.0 include:

  • Cabbage
  • Cucumber
  • Geranium
  • Periwinkle
ph tester soil

Factors affecting soil acidity


Rainfall contributes to a soil’s acidity. Water (H₂O) combines with carbon dioxide (CO₂) to form a weak acid — carbonic acid (H₂CO₃). The weak acid ionizes, releasing hydrogen (H⁺) and bicarbonate (HCO₃). The released hydrogen ions replace the calcium ions held by soil colloids, causing the soil to become acidic. The displaced calcium (Ca⁺⁺) ions combine with the bicarbonate ions to form calcium bicarbonate, which, being soluble, is leached from the soil. The net effect is increased soil acidity.

Nitrogen fertilizers

Nitrogen levels affect soil pH. Nitrogen sources — fertilizers, manures, legumes — contain or form ammonium. This increases soil acidity unless the plant directly absorbs the ammonium ions. The greater the nitrogen fertilization rate, the greater the soil acidification. As ammonium is converted to nitrate in the soil (nitrification), H ions are released. For each pound of nitrogen as ammonium, it takes approximately 1.8 pounds of pure calcium carbonate to neutralize the residual acidity. Also, the nitrate that is provided or formed can combine with basic cations like calcium, magnesium and potassium and leach from the topsoil into the subsoil. As these bases are removed and replaced by H ions, soils become more acidic.


Legumes like soybeans, alfalfa and clovers tend to take up more cations in proportion to anions. This causes H ions to be released from plant roots to maintain the electrochemical balance within their tissues. The result is a net soil acidification.

Subsoil acidity

Even if the top 6 inches of soil show a pH above 6.0, the subsoil may be extremely acidic. When subsoil pH‘s drop below 5.0, aluminum and manganese in the soil become much more soluble, and in some soils may be toxic to plant growth. Cotton and, to some extent, soybeans are examples of crops that are sensitive to highly soluble aluminum levels in the subsoil, and crop yields may be reduced under conditions of low subsoil pH. If you’ve observed areas of stunted plants in your field, take a subsoil sample in these areas. If the soil pH is extremely acidic (below 5.2), lime should be applied early in the fall and turned as deeply as possible.

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