Knowing your garden soil's pH level, and then effectively applying this number, can go a long way in learning what makes your garden "tick".  It can help troubleshoot issues you're having in growth and yield.  It can also take a garden that's producing well to the next level.

  In this two-part series, we'll look at what pH is, and what to do with it once you know it.

  First, what is pH?

  The pH describes the relative acidity or alkalinity of your soil’s makeup, and it has important implications for plant health and growth. Soil pH impacts beneficial fungi and bacteria in the soil and influences whether essential minerals are available for uptake by plant roots.

  A solution’s pH is a numerical rating of its acidity or alkalinity. All pH is measured on a logarithmic scale from zero (most acidic) to 14 (most alkaline, or basic); 7.0 is neutral. The pH scale is used by chemists to measure the concentration of reactive hydrogen ions (H+) in a solution.

  Most food crops prefer a pH of 6.0 to 6.5, but you can have a productive food garden as long as your pH is about 5.5 to 7.5. A difference of just 0.5 may not seem like much, but the pH scale is logarithmic, which means, for example, a pH of 7.0 is actually 10 times less acidic than a pH of 6.0. Potatoes and most berries, which grow best in more acidic soil, are the main exceptions to the average preferred pH range.

  A soil’s pH results from interactions among native rocks, plants and weather conditions over many years, and it varies with climate and physical surroundings. In moist climates that support dense forests, such as those east of the Mississippi River and along the Pacific Coast, soil tends to be acidic, with pH ratings usually between 4.0 and 5.5. The grasslands of the comparatively dry Midwest often have slightly acidic soil (6.0 to 6.5), while most arid regions, such as the Rocky Mountains, are dominated by alkaline soil (7.0 to 7.8). Local differences in rock can cause huge variations within these general patterns, however — for example, when weathered limestone creates alkaline patches in otherwise acidic landscapes, or when elevation leads to more or less rainfall. Plus, soil is often severely disturbed during construction, and sometimes native topsoil is completely lost.

  Alkaline soil occurs naturally in places where soil is formed from limestone or other calcium-rich minerals, and high water-evaporation rates common in arid climates aggravate the problem by loading the topsoil with accumulated salts. Many garden plants can still thrive when grown in alkaline soil that has been generously enriched with organic matter, which also improves the soil’s ability to retain water. Mulches also will slow the buildup of salts in plants’ root zones by reducing the amount of surface evaporation.

  The next post will discuss how to test your soil, and give some simple methods to affect it.

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