Tending the plants you grow: Soil Testing

Good gardeners and farmers know how to tend the plants they grow. They know what and when to plant, and how to respond to issues like pests, diseases, and abnormal weather to have good results. Great gardeners and farmers, on the other hand, know that tending the soil where their plants grow is the first, and most important, step to growing with the greatest results.

As an extension agent, I’ve heard more than once from colleagues that the best farmers are soil farmers — they take care to plan their practices based around the health of the soil. It totally makes sense — the health of the plants you grow in the soil is largely dependent upon the health of the soil. You must remember that the plants are only a small fraction of the life that is in or supported by the soil.

In his book “The Unsettling of America: Culture and Agriculture,” celebrated author, poet, and agriculturist Wendell Berry notes that, “The soil is the great connector of lives, the source and destination of all. It is the healer and restorer and resurrector, by which disease passes into health, age into youth, death into life. Without proper care for it we can have no community, because without proper care for it we can have no life.”

The importance of soil to human life and health led the United Nations Food and Agriculture Organization to deem 2015 the International Year of Soils. Loss of healthy, arable soil is one of the critical issues facing many countries who are already struggling with hunger and malnutrition. Without good soil, we cannot produce good food.

Back here at home, many gardeners sometimes fail to see that it isn’t just what you plant but how you care for the soil year round that makes your garden a success. Many gardeners treat their soil and fertility as an afterthought, relying on quick fixes like water soluble fertilizers to feed their plants while ignoring the bigger picture.

Soil health relies on a number of different factors. The first step is to assess the soil. My regular readers know that I say it often, but soil testing is important for gardens of any size. A soil analysis will provide a snapshot of soil chemistry, the level of element-based nutrients, for the sample. Many of these nutrients are minerals, broken down from the parent rock material. This forms the backbone of the soil. Fall is really the best time to test soil, since it can take several months for amendments like lime to break down and be incorporated into the soil. Waiting until spring when you are planting the year’s first garden will mean that it will be too late to get the soil amendments incorporated.

Plants have a number of essential plant nutrients that they need from the environment in order to properly grow and function. Hydrogen, carbon and oxygen are all important, but are not something that gardeners have to supply since they are taken in by the plant in the form of water and carbon dioxide (unless you forget to water your plants, like I sometimes do — but death will occur from dehydration well before lack of hydrogen).

There are six soil macronutrients, which means that they are used in larger amounts by the plants. These include nitrogen, phosphorous, and potassium, which form the basis of most common fertilizers that have those magic three numbers on them (example: 10-10-10). Those three numbers indicate that the fertilizer contains that percentage of the elemental nutrient in it. For this example, the fertilizer contains 10 percent nitrogen, 10 percent phosphorous, and 10 percent potassium.

The other three soil macronutrients are magnesium, sulfur, and calcium. Whatever fertilizer you choose, a soil test will allow you to add the right amount to ensure proper growth without under or over fertilizing.

Here in West Virginia, we usually add calcium and magnesium in the form of lime, since we also need to raise the pH of the soil. Sulfur is most commonly found in the breakdown of organic matter, so as long as you add fresh matter such as compost, you are usually covered.

Soil micronutrients are needed in much smaller amounts. Those nutrients are boron, copper, chlorine, manganese, molybdenum, and zinc (remember the periodic table?). These are also usually supplied from organic matter, so you don’t usually have to supply them if you are incorporating compost.

Maintaining a soil pH in the 6 to 6.5 range is very important for gardeners. At this pH, the soil chemistry is optimum to make the nutrients available to the plant. If the pH is too low or too high, you can add all the fertilizer you want, but it won’t be available to the plant.

The one exception is for plants like blueberries, azaleas, and Rhododendrons that require lower pH ranges. The reason is not that they like acidic soil, per se, but that it makes iron more available to them. They are heavy iron feeders and require larger amounts than other plants.

Aside from providing micronutrients, addition of organic matter such as compost also improves soil structure and feeds the bacteria and fungi that are part of the living soil food web. Heavy clay soil (which is common in West Virginia) can be too dense to support healthy plants, since the clay particles are so small they stick together and do not leave space for air. This can be aided with the addition of compost, which improves the porosity (air pockets) in the soil.

3 thoughts on “Tending the plants you grow: Soil Testing

  1. What is the proper pH for potatoes and sweet potatoes? Do they need an abundance of any particular element?

    John White

    1. Mr. White – potatoes prefer a slightly acidic pH between 5.3 to 6.0. I would keep it in the 5.5 range – the higher your pH, the more likely you are to get disorders such as scab. Sweet potatoes prefer a pH in the 5.8 to 6.5 range.

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