Nutrition is nearly as important to plants as it is to humans. Understanding fertilizers and how they work with plants and soils is imperative to a healthy garden. Nutrients act differently from one another and in function in a different way in other types of soils. “Plant food” is a phrase that is somewhat misleading. We can not feed plants; they produce their own food through the process of photosynthesis. We can supplement their nutrition through fertilizers.
Most all purpose fertilizers are made up of thee essential elements. The analysis of nitrogen, phosphorus, and potassium is represented by the three numbers found on the bags of fertilizer (like a10-10-10). The numbers10-10-10are the analysis of the elements in the order of nitrogen, phosphorus, and potassium. The order stays the same on any bag of fertilizer. The numbers can vary on specialty fertilizers that feature a higher percentage of one nutrient to the other two. Super phosphate is a good example being a 0-40-0 analysis. There is no nitrogen or potassium in this fertilizer, just phosphorus with would be good for root establishment or bud development. Nitrogen is an extremely important element to plants. Nitrogen plays a vital role in many plant processes. The typical response that we as gardeners see is the greening of foliage and new leaves or shoots. Phosphorus helps promote root growth, helps plants be more tolerable of adverse conditions, and can stimulate bud and seed development. Potassium helps improve water retention, promotes growth, aids in photosynthesis, and has many other functions. These three elements are considered the “essential nutrients”, and obviously help perform the most vital tasks of plant life. There are many other nutrients that we consider “micronutrients” that also aid in other plant processes. Many of these can also be found in all purpose fertilizers.
Soils play a major role in a plants ability to obtain nutrients. I hear a lot of people talk about how terrible their clay soil is. It is easy to understand their resentment of clay because of the effort it takes to dig a hole in compacted clay and rock. The truth is that most clay soils have the ability to be wonderfully nutritious for plants. Without going into too much chemistry, clay particles have the potential to hold many more ions than other soil particles like sand or loam. Remember the phrase “opposites attract”? This is the same thing. The positive and negatively charged soil particles and fertilizer elements hold to one another in a fashion that eventually makes them available to the plant. Sand and loamy soils do not have the same amount of attraction as clay soils. What does all of this mean? Clay soils can be really nutritious soils and not require too much supplemental fertilizer while sandy and loamy soils can need fertilizer on a more frequent basis.
Having a soil test is something that I recommend for any gardener about every other year. Fertilizing (or liming) on a yearly basis is pointless unless you know what needs to go in your soil for your garden to be efficient. The process of taking a soil sample is pretty simple. All you need to do is pull away any mulch, plant material, or grass and take about a cup full of soil to place in a brown paper bag. Plastic bags retain too much moisture and can change the properties of the soil. Some great information about soil samples and where to turn them in can be found here: http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-30/#SubmittingtheSample
This is a free service offered by the North Carolina Division of Agriculture. I recommend avoiding taking samples during the late winter months as many farmers have submitted their samples at this time. You will get quicker results at other times of the year. Several weeks after you have taken your soil sample, you will receive the results in the mail. The results can be somewhat difficult to understand. Feel free to bring them to the garden center and we will help you decipher the results. One really important piece of information that is included in the report is the soil pH. The pH of your soil can greatly affect the uptake of certain nutrients and micronutrients. A pH in the range of 6.0 to 6.5 is what we consider ideal for many of our plants here in the piedmont ofNorth Carolina. A more alkaline (higher) pH results in plants having difficulty obtaining iron, copper, boron, zinc and other nutrients. A more acidic pH (lower) makes the uptake of nutrients like nitrogen, phosphorus, potassium, sulphur, calcium, and magnesium more difficult. Soil tests will almost always recommend the application of nitrogen regardless of what the garden contains. It is important to note that nitrogen does not stay in the soil for any great length of time. Most unused nitrogen will be leached out of the soil or mixed with runoff to flow into our rivers and lakes. Please make sure that the proper amount of nitrogen is applied to turf and landscape areas.
Hopefully this quick overview of plant and soil nutrition was not too boring. There is obviously much more to know about this topic and I welcome any questions that you may have. I can not stress enough the importance of a soil test, knowing your pH, and applying the correct amount of fertilizer. Understanding these three things will help keep our environment clean and our gardens beautiful.