Last week I discussed amending soil to improve the structure so that it is beneficial for the kind of plants you want to grow. This week we will discuss nutritional amendments.
Clay soil, which is what most of us have, does a good job of retaining nutrients. The makeup of our soil (mainly the high alkalinity) often prevents plants from using nutrients that are in the soil. Amendments can be incorporated into the soil to change its chemical composition such that nutrients in the soil can be released for plant use.
Plants need 16 elements for normal growth. Nitrogen, Phosphorus, and Potassium (NPK) are the main elements we add to our lawns, gardens, and potted plants. These are the most visible on the labels of products we purchase to feed our plants and soil, but sometimes other elements are needed also. If so, you must read the fine print on the labels and/or purchase different products from those you commonly use.
As previously mentioned regarding soil structure, a soil test should be performed before adding amendments willy-nilly. A good soil test will identify your soil’s need for specific nutrients and if you have too much of something, that will also be identified.
The alkaline nature of our soil is difficult and expensive to change very much for very long. It can be mitigated to a degree for some time, but the best approach in dealing with this characteristic is plant selection, working with the condition rather than trying to substantially change it.
Lowering the pH of soil (to make it less alkaline) requires ongoing addition of amendments. Once again compost helps with this problem. It provides organic matter to feed soil critters that, in turn, enrich the soil and help make nutrients available to plants. Sulfur is the primary element used for appreciably lowering alkalinity. The frequency and cost will depend upon the product you use, the amount that you are lowering the pH, and the amount you need.
Greensand helps change texture and contains some trace elements but is expensive. I mention this simply to make the point that sometimes a product can do double duty. Check labels carefully.
There are many organic and synthetic products available to correct nutritional deficiencies. Some common amendments are fish meal, blood meal, bat guano, gypsum, diatomaceous earth, and lime. Lime is used to raise the pH of soil, so it should not be used here despite it often being recommended by gardening experts, who are generally from other areas with acidic soil.
Gardeners in this area who grow roses sometimes give their roses a tablespoon of Epsom salt which contains magnesium and sulfur. This must be added with care to avoid building up too much magnesium in the soil. Very little magnesium is used by plants.
As with amendments that change soil texture, do appropriate research before adding nutritional amendments. Also keep in mind that more is not better and can be harmful. Add only the recommended amount to correct the problem.
This article originally appeared on Amarillo Globe-News: Garden Guy writes more about soil and the 16 elements plants need
Reporting by By Bob Hatton, Special to the Amarillo Globe-News / Amarillo Globe-News
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