Garden Q&A: Proper alkalinity vital to plants
Question: We took a soil test last fall, and the results said that our pH is too low. It said we need to add lime to fix this. The test results told us how much to add, but we don't know what to buy or how to do it.
Answer: Here in Western Pennsylvania, our soils are clay-based and often too acidic for optimum plant growth. The pH scale runs from 0 to 14, with measurements in the 0-to-7.0 range being acidic and those above 7.0 being alkaline. A pH of 7.0 is neutral.
Soil pH is important to plant growth because it determines the availability of almost all essential plant nutrients. When soils become too acidic, certain nutrients (such as phosphorus) become less available, beneficial soil bacteria are less active, and certain elements — like aluminum and manganese — can become toxic. Not to mention the fact that your plants simply won't perform their best. This is true no matter what you are growing — veggies, lawns, perennials, etc.
And so we are told to use lime to raise the soil's pH and make it less acidic. Our goal in most gardening situations is to adjust the pH to 6.5. This is the “magic number” at which the most nutrients are available in optimum amounts. Some plants (including evergreens, rhododendrons, azaleas and blueberries) prefer acidic soils, but the large majority of the plants growing in your vegetable patch need a pH of about 6.5 to maximize their yields. It is important to conduct a soil test every few years to determine your soil's pH and fertility levels.
Liming materials are not all created equal. First, look to your soil test results to determine if you need calcitic lime or dolomitic lime. Calcitic lime is mined from natural limestone deposits and crushed to a fine powder. It also is called aglime or agricultural lime and supplies calcium to your soil as it adjusts the pH. Dolomitic lime is derived in a similar manner but from limestone sources that contain both calcium and magnesium.
If your soil test came back showing high levels of magnesium, use calcitic lime. If the test shows a magnesium deficiency, then use dolomitic limestone instead. Clay soils tend to hold onto magnesium, so more often than not, calcitic lime is the more appropriate choice in Western Pennsylvania.
Next, look for pelletized calcitic lime. This product is created by taking the finely pulverized particles of lime and binding them with a compound to form small pellets that are much easier to spread than powdered lime products and will keep you from getting covered with dust. Uniform coverage is very important, as lime is insoluble and can't move around within the soil.
Skipped areas won't have an effective pH change, and overlapped areas will undergo a more drastic pH change and wind up with potential trace element issues. To cover the area evenly, use a drop spreader to spread half the pelletized lime in one direction over the entire area, then apply the rest in a perpendicular fashion, creating a crisscross pattern.
Pelletized lime is only slightly more expensive and is well worth it for its ease of application and convenience.
Keep in mind that the pH change from adding lime is not permanent. You'll have to retest your soil every three or four years and add more lime as the results indicate.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.
Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
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