Soil conditions may be a mystery because gardeners have heard of the term "soil pH" but know little about it. So, what is soil pH and why is it important?
The scale for measuring acidity or alkalinity contains 14 levels known as pH units. Numbers less than 7 are acidic, and numbers more than 7 are alkaline. They appear to be simple, but at each step they change by a power of 10.
For example, a 5.5 pH is 10 times more acidic than a 6.5 pH, a 4.5 pH is 100 times more acidic than a 6.5 pH, a 3.5 pH is 1,000 times more acidic than a 6.5 pH; and
8.5 pH is 10 times more alkaline than a 7.5 pH, etc.
You may be familiar with the condition of the soil as being acidic, neutral or alkaline. The pH level of the garden soil is an indication of how the roots of all plants will assimilate the fertilizer elements.
A soil test will determine the pH level of your soil. Information is available at AgriLife Extension Office (823-0129) or online at http://soiltesting.tamu.edu.
Chemical properties of soils are important in that they regulate the elements to the roots. Fertilizer elements may be in the soil, but if the pH level is not suitable the plants will have symptoms of a deficiency. The best pH range for the roots to absorb the elements is:
* 5.0-6.5 pH: Manganese
* 5.0-7.0 pH: Boron, Copper, Zinc
* 6.0 or higher pH: Potassium
* 6.0-8.0 pH: Nitrogen
* Lower than 6.5 pH: Iron
* 6.5 or higher pH: Calcium, Magnesium
* 6.5-7.5 pH: Phosphorus
Sam Cotner writes in The Vegetable Book that symptoms of deficiency for the elements are:
* Nitrogen (N): Plants stunted, yellowing from bottom up and leaf tip back to petiole. Reduced size. Slow, stunted growth.
* Phosphorus (P): Plants stunted, short internodes, purple or dark green foliage; old leaves die back; flowers and fruit are poor. Slow growth, delayed maturity.
* Potassium (K): Older leaves scorched on margin; weak stem; fruit shriveled; uneven ripening.
* Calcium (Ca): Young leaves turn yellow, then brown; growing tip bends; weak stem; short dark roots.
* Magnesium (Mg): Leaves are thin, lose green color from between veins from bottom of plant up; tend to curve upward.
* Manganese (Mn): Tissue between veins turns white; leaves have dead spots; plant is dwarfed.
* Boron (B): Tip of growing plant dies; bud becomes light green; roots are brown in center; flowers do not form.
* Zinc (Zn): Terminal leaves are small; bud formation is poor; leaves have dead areas.
If any of these symptoms occurred with your garden plants, then you should have soil samples tested.
Most vegetables and fruits will tolerate a relatively wide range of soil pH. A soil test is the only tool to determine the pH of your garden soil. The test report will let you know what should be applied to correct its condition when warranted.
If the soil is excessively alkaline, the application of a soil-acidifying agent will improve plant health and growth. If the soil is excessively acidic, the application of agricultural limestone will improve plant health and growth. Powdered limestone requires about three months to increase the pH, and pelleted limestone requires more time to change the soil pH.
Soil pH is a critical factor often overlooked by many gardeners. The best soil pH range for vegetables is:
* 4.8-6.5 pH: Irish potato
* 5.5-6.5 pH: Sweet potato
* 5.5-7.0 pH: Carrot, cucumber
* 5.5-7.5 pH: Cauliflower, tomato
* 5.8-7.0 pH: Onion
* 6.0-7.0 pH: Broccoli, lettuce, melons
* 6.0-7.5 pH: Beet, cabbage, spinach
* 6.0-8.0 pH: Asparagus
The best soil pH range for fruits is:
* 4.0-5.0 pH: Blueberry
* 5.0-6.5 pH: Apple, strawberry
* 5.5-7.0 pH: Red raspberry
* 6.0-7.0 pH: Apricot, sour cherry
* 6.0-7.5 pH: Sweet cherry, crabapple, peach, pear, pecan
* Write to Elmer Krehbiel, Master Gardener, c/o Brazos County Office, Texas AgriLife Extension Service, 2619 Texas 21 W., Bryan, Texas 77803. His e-mail address is elmer.krehbiel@theeagle.com.
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