Healthy soil is the basis for healthy trees and shrubs. But all soils are different. The characteristics of the soil as well as nutrient levels vary from site to site. With this in mind, the best way to fertilize your trees and shrubs is to do so on the basis of a soil analysis.
What’s in the Soil?
Soil contains macronutrients such as nitrogen, phosphorus and potassium as well as micronutrients like iron and zinc. These nutrients are necessary for plant growth, but are not always present in the soil at appropriate levels. When you purchase over-the-counter fertilizer blends, most do contain the most commonly deficient macronutrients. However, secondary nutrients and micronutrients are often missing from store-bought options despite playing a critical role in growth, photosynthesis, and defense against disease and insect problems.
Iron, for example, is important in photosynthesis, but is quite often deficient in leaf tissue. This may even be the case when there is iron present in the soil because the pH of the soil (acidity or alkalinity) can influence nutrient availability. At high pH values (above neutral 7), iron is unavailable for uptake, whereas at more acidic soil pH (4.5-6.5), it is readily available. Often, an iron deficiency is actually a pH issue, identifiable only by soil analysis.
Beyond nutrients, organic matter in the soil is also important. Naturally, it comes from decomposition of things like plants, roots or or even animals. Its presence improves soil structure, helps with water retention and provides other benefits.
Amending the Soil
Soil management standards specify that there should be a goal in order to fertilize. Common goals are to enhance growth or improve appearance. You can achieve these goals by adding amendments to the soil to meet plant needs, adjust pH issues, or correct nutrient deficiencies. However, you can’t know what your soil needs without first knowing what it already has! Soil analysis helps identify the current make-up of the soil, identifying any deficiencies, specifying the pH level and determining the amount of organic matter present. This analysis ensures fertilization and soil amendments adequately address any issues while also reducing the potential for over-applying nutrients.
If over-the-counter fertilizers are applied in excess, a number of problems can develop. Misapplication can actually harm the soil and result in competition among nutrients for uptake. Further, excess nutrients can be a source of surface and ground water contamination. One well-known issue is associated with phosphorus run-off into fresh water. The excess nutrients promote algae growth that may then result in fish kills. Interestingly, our soil samples find that in most areas there is already ample phosphorus in the soil. Therefore, most Bartlett-developed treatments are phosphorus-free.
Not all Fertilizers are Created Equal
Soil nutrient products with a slow-release nitrogen source help ensure nutrients stay in the root zone. This means nutrients are available for plant uptake rather than leaching through the soil into the water table. Further, for best results, the ideal fertilizer will be specific to the soil in question and the plants growing there. A blend based on soil analysis and plant species will result in maximum benefit and minimal environmental impact.