In the last post we found out what pH was, some generalizations of soil pH based on the region you live in, and what it means. Today, we'll look at how to test for soil pH, and give some basics on how to affect the number.

  If your crops seem to be thriving, then you probably don’t need to worry much about your pH. But if you find that plants just don’t seem to be growing as well for you as they do for your neighbors, then the problem could be related to pH and you should probably have your soil checked with a pH test. The cost for basic soil evaluation done by a state soil-testing lab ranges from free to $25, depending on the state in which you live, and typically includes a pH test along with results for major and sometimes minor nutrients. Soil-test kits with detailed instructions are usually available at extension service offices, or you can order them by mail.

  If one bed or small section of your garden goes wonky, you might try a home pH test kit rather than waiting on lab results. When a team of Missouri extension experts submitted soil samples to 82 soil-testing laboratories and compared the lab’s results with those from do-it-yourself pH-measuring kits, the $20 LaMotte home color kit (available at Peaceful Valley Farm & Garden Supply ) earned high accuracy ratings. Personally, I like pH color kits because they are fun to use, and a practiced eye can detect the small changes in color between shades of orange (acid) and green (neutral to alkaline) in the test results.

  Raising the organic matter content of soil will usually move the pH of both acidic and alkaline soils toward the neutral range. This is because organic matter plays a buffering role, protecting soil from becoming overly acidic or alkaline. Finished compost usually has a near-neutral pH, so regular infusions of compost should be the primary method you use to improve soil with extreme pH issues. If your pH readings are only slightly acidic or slightly alkaline, compost and organic mulches may be the only amendments you need to keep your crops happy and your garden growing well.

  The standard intervention for overly acidic soil is to amend it with lime, an inexpensive soil amendment made from ground limestone that slowly raises the pH over a period of months. Products labeled “dolomitic lime” are usually preferred because they contain both calcium and magnesium. But if you have dense soil and a soil test indicates excess magnesium (which can tie up nitrogen), you should use low-magnesium, calcium-rich powdered crab or oyster shells as your liming material. Read and follow the label, because products differ in application rates, which, in turn, vary with soil type. You can’t apply a correct amount of lime unless you know your soil’s pH first, and if you apply too much, it will be extremely difficult to correct. Err on the cautious side by applying too little lime at first.

  After the pH of acidic soil is raised above 6.0 using organic amendments and dolomitic lime, I’ve found it can be maintained with a light, yearly application of alkaline woodstove ashes. In addition to containing enough calcium and magnesium to have a liming effect, wood ashes contain an array of micronutrients, too. The key is to use them sparingly, in small, dispersed amounts, and to never add wood ashes or lime to soil with a pH higher than 6.5. A quart of wood ashes (1 pound) is about right for 50 square feet of cultivated space. When you have a lot of ashes to spread, apply no more than 20 pounds of ashes per 1,000 square feet of garden bed.

  If you are not using acidic chemical fertilizers, a normally acidic soil may not require liming again for several years, if ever. Then again, if your soil is porous sand in a high-rainfall area, pH testing may show a need for liming every other year. Just be careful to never apply lime unless a pH test shows it is needed, and never use it where you are growing plants that prefer acidic soil conditions, such as blueberries and azaleas.

  If you have exceptionally alkaline, high-pH soil, you can often tame it by adding organic matter and powdered sulfur. However, sulfur may do little good in alkaline soil that is rich in free lime, also known as calcium carbonate. You can test for free lime by covering a soil sample with vinegar; if it bubbles, you have free lime and should consider gardening in beds filled with non-native soil.

  Extension experts in places where alkaline soil predominates emphasize that most plants will grow well in organically improved soil with a pH as high as 7.5, and improving soil quality with organic matter — rather than lowering the pH — should be your primary goal. Alkaline soil can be stubborn about releasing its valuable phosphorus to plants, so amend it every chance you get with composted manure, which has been found to solve several problems associated with high pH levels. The humic acids in both composted manure and vermicompost help make phosphorus available to plants grown in alkaline soil, as does the presence of rotted plant tissues from both regular compost and cover crops. Acidic mulches, such as pine needles, can help lower soil pH slightly, but other mulches, such as bark or wood chips, have little effect on soil pH.

  Special thanks to for the information!

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