Thursday, July 2, 2009

pH is Sexy!

     OK, pH - the measurement of the alkalinity or acidity of your soil - may not exactly be sexy. But (and this is a stretch), according to Webster's Collegiate Thesaurus, the second synonym for "sexy" is "blue". And if you have ever conducted a pH test with a LaMotte Soil Test Kit, you know that the blue color that might be the end result of that mix of soil and pH indicator fluid is a very desirable color, indicating a very sexy pH of 7.0.

How sexy is a pH of 7.0?

     The "pipeline" for the nutrients in the soil going to your plant roots is the largest when the pH is in the neutral range, about 7.0. Actually, if your soil tests in the range of 6.5 to 7.5, virtually all types of plant foods and essential chemicals become more available to the plant roots for uptake.

     Some plants, though, prefer soil that is slightly to strongly acidic, including rhododendrons, azaleas, camellias, gardenias and holly. Fruits and vegetables that prefer a pH range of 5.5-6.5 include lima beans, carrots, potatoes and strawberries. Most other vegetables prefer a pH between 6.0 and 7.0.

     So, let's say you test your soil pH and the result is strongly acidic (4.0-5.5). How can you raise the pH to make your soil more alkaline? Add lime. How much lime? The following chart's recommendations can raise your soil pH by 1 point:

     The lime should be incorporated into the soil by either turning it in by hand or by rototilling. Hydrated lime or finely ground limestone is available from most yard and garden centers. But handle it carefully, wear protection and follow the manufacturer's instructions. 
     If you need to apply more than 20 ounces of lime per square yard, you should apply half of the total amount required each six months and checking the adjusted pH before the second application. If you plan to adjust the pH of your soil, it should be done in the fall before the winter rains.

     How about if your soil pH is too alkaline (8.0-10.0)? Increase the quantity of organic matter. Organic materials are decomposed by soil bacteria and other organisms generating complex organic acids. These acids can help lower the soil pH, but because the amount and type of organic acids generated depends on the type of organic matter being decomposed, the type of soil, the temperature as well as overall numbers and activity of bacteria and other organisms, so the amounts required can only be approximated.

     In general, to reduce the soil pH by 1.0 unit, the estimated application rates (thoroughly mixed into the soil by hand or using a rototiller) for various organic soil amendments is as follows:

    •    Peat moss - approximately 2.5 pounds per square yard
    •    Compost - approximately 14 pounds per square yard
    •    Manure - approximately 5 pounds per square yard

     Another approach is to use acidifying fertilizers. Generally, such products are applied at a rate of approximately 2 to 3 ounces per square yard, and typically lower pH by about 1.0 unit. This approach is usually not a satisfactory approach to long term pH adjustment, since the effects are very short lived.

     Another approach used is the application of ground rock sulfur. The typical application rate to reduce pH by 1.0 unit is to apply the ground rock sulfur at approximately 1 ounce per square yard on sandy soils, 1 to 2 ounces per square yard on loam soil, and 1 to 3 ounces per square yard on clay soils. Ideally, the sulfur should be thoroughly mixed into the soil in the fall and checked periodically to see when a new application may be necessary.

     This information came from a variety of sources, including the University of California, the Lamotte Soil Handbook and various other governmental agencies.

And to answer your first question: What the heck does "pH" stand for? Potential Hydrogen Ions. The scientist that developed this concept in 1909, a Danish chemist named Sorensen, originally wanted pH to stand for: "the power of Hydrogen". And that is definitely more sexy.

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