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Soils
and pH
How important is soil to the success of gardening here in the Central Valley? Tulare has moved ahead of Fresno as the leading agricultural county in California, so we must have good soil in our home gardens right? Well, maybe yes and maybe no! While volunteering as a Master Gardener I talked to a homeowner in a new subdivision that until recently had been a pasture for years. He determined the soil pH was 7.5 with a test kit that he purchased at a garden center and wanted to know if that was normal for this area. I told him soil pH could vary widely from one side of the street to the other but, generally, soils in dry climates such as ours tend to be alkaline and those in high rainfall areas tend to be acid. Plant roots absorb water, which is then channeled throughout the entire plant. Along with water plant roots absorb minerals that are dissolved in the soil water, which are essential for plant growth. The pH is a measure of the acidity or alkalinity of the soil and indicates whether minerals dissolve in water or remain as a solid in the soil. The pH affects soil life, soil structure (porosity and density), nutrient availability, and ultimately plant growth. The power of hydrogen (pH) is measured on a scale of 1-14. A pH of 7 means the soil is neutral. A pH below 7 indicates acidity; one above 7 indicates alkalinity. Most plants grow best in soils with a pH between 5 and 7. When the pH is 5 and below, nitrogen, phosphorus and potassium become less available to plants, earthworms disappear and bacteria become less active. When the pH is 8 and higher, iron and zinc become less available to plants, chlorotic leaves develop, and salt burn from sodium and boron tend to occur. Alkaline soil is high in calcium carbonate (lime) or other minerals like sodium. Sodium impedes water infiltration in the soil. Deep watering can help lessen salinity, but only if the soil drains quickly. Some alkaline soils are high in sodium and low in calcium carbonate. Amend with gypsum and apply liberal amounts of water to leach away the sodium. Many plants grow well in moderately alkaline soil, which predominates in the Central Valley. Very rarely do we want to make our soils more alkaline but in other parts of the country where soils are very acidic, gardeners amend with lime to raise the pH. Yams, peppers, parsley and legumes are a few plants that like a slightly alkaline soil. Surprisingly, clematis and spinach prefer a pH of 8.0. Slightly alkaline soils can be amended to grow acid-loving plants like azalea, camellia, gardenia, heather, hydrangea, and rhododendrons by adding composted manure, peat moss, ground bark, and periodic applications of iron and zinc chelates. Mulch these plants with evergreen needles or leaf mold. Sulfur has also been used safely for years to lower pH but be careful not to overuse. You don't have to test a soil's pH. I've never tested mine. However if you are losing prized plants, then consider purchasing a kit to satisfy your curiosity or just add composted steer manure to the soil. It may take a year or two to appreciate the real improvement, but the use of organic material will help bring your soil pH to neutral. Try adding two to three inches per year to the flower beds and vegetable garden and you'll be amazed by the plant growth. Steer manure is available in easy to handle bags and it is inexpensive for the amount of value it provides. If you don't have the time or inclination to till it into the soil just spread it, add water and let the earthworms do the work. You will encourage growth above and below the soil. You will help your soil reach the "neutral zone" and increase your chances of having a beautiful garden.
July 25, 2002 |