The big three mineral elements of plant nutrition are nitrogen, phosphate and potassium, somewhat closely followed by calcium, and then far after these are the trace minerals: magnesium, boron, manganese, sulfur, iron, zinc. Even more minimally are copper, cobalt, molybdenum, chlorine and others.
With the exception of calcium, the best way to assure the very small amounts of these minerals that are needed are present in your soil is to have generally good soil, because good soil contains these in the trace amounts that plants require. The first step to good soil is compost and a soil pH ranging near 6.5.
Compost by its nature will generally supply the trace minerals in the normal amounts that plants have evolved a need for. (Equally, too large — and this is a very small “too large” — an amount of any of these can be toxic to your plants; compost will not contain these in toxic amounts without determined effort). Proper pH in turn will assure that soil minerals already present are “plant available,” for plants generally cannot take up the minerals they need when soil pH is at extremes. Only a professionally done soil test can tell you what your soil deficiencies are along with how to correct its pH.
In Boone Country, achieving good soil pH generally means raising the pH by applying lime, and liming generally contributes often needed calcium (particularly if in the form of calcium carbonate) and some forms of lime (dolomite lime) contribute magnesium as well.
In particular a calcium deficiency is the cause of “blossom end rot” in tomatoes, peppers and sometime squash and other vegetables, recognized as a dry brown-gray sunken unappealing decay on the blossom end (the end away from the stem) of the fruit.
Achieving a good calcium and pH environment in your soil takes time and is influenced by, and in turn influences, a multitude of soil factors beyond the scope of this article. A soil test is the best way to go: for example in clay soil, 8.75 pounds of lime per 100 square foot raises the pH one point, while in light sandy soil, 2.5 pounds per 100 square foot also raises the pH one point.
The remaining trace minerals contribute in various ways to your plants. Magnesium is the only earth element used in the build-up of chlorophyll. The exceedingly small amount of needed boron, excessive amounts are toxic, regulates the metabolism of carbohydrates in plants. Your plants cannot transform nitrogen into amino acids without molybdenum. Remaining trace elements act in similar ways, crucial if lacking, but hardly used at all.
The signs of deficiency in these and the remaining elements tend to be the yellowing or curling of leaves, but these are signs with many causes. A soil test and resulting good soil is again the best approach.
When I learned soil copper influences the sweetness of fruits it immediately reminded me of an annual summer experience: how the Fuji apples that occasionally appear here from New Zealand (when it is fall there) are incomparably sweeter and better than the typical Fuji apples from Washington state arriving at any time of year, despite their presumably identical genetics. It too is commonplace for me that the vegetables, and their dishes, that I’ve experienced in Europe are typically several points higher on the taste scale than any I’ve generally tasted here, including even my own vegetables, grown as well as I can. While less extreme climates elsewhere have some effect it is my instinct — and I have no proof at all — that, given the identical genetics, the presence of trace minerals must play some significant role in these taste differences. This quality of taste and goodness is my measure of a successful garden and more research on the topics of taste and trace will follow.
There are commercially available trace mineral supplements for your soil. Here is the formulation for one of these, known as STEM (Soluble Trace Mineral Mix): sulfur, 13 percent; boron, 0.025 percent; iron, 7.50 percent; copper, 2.3 percent; manganese, 8.0 percent; molybdenum, 0.04 percent; zinc, 4.50 percent. In use, carefully understand from the labeling when and how such mixes may be gainfully applied.
Dennis Sentilles, MU professor emeritus of mathematics, is a Missouri Master Gardener and a member of Katy Trail Slow Food International with a love for working outdoors and eating simply and well every day. He can be reached at firstname.lastname@example.org.