Appropriate levels of nutrients in the soil are needed to achieve good sustained plant growth. The main elements of nitrogen, phosphorus and potassium are the most critical. As such, some of these elements may need to be periodically added to achieve that best plant growth. Of these main elements, phosphorus and potassium are the most likely to reach a level in the soil of home gardeners where future applications can be few and far between. This is because those elements are harder to leach from the soil and aren’t normally used in such high quantities each season as nitrogen.
Submitting a soil test to a quality lab every three to five years will show you the levels of phosphorus and potassium in your soil and whether there is a need to apply more. Nitrogen is water soluble and can be leached from the soil with inappropriate watering. Since nitrogen is the nutrient responsible for rapid leafy green growth, it needs to be applied to the soil each and every year.
Should your soil test show that you need to apply any of these nutrients there are options for how to do so. Conventional fertilizers often offer all three main nutrients in similar amounts, such as a 16-16-16 application; in varying amounts, such as a 28-3-10 application; or as single nutrients, such as in a 21-0-0 application. These fertilizers are usually fast-release and provide nutrients to the plants quickly, but it is possible to find formulations that are encapsulated for slower release over time. You can also find conventional fertilizers with micro-nutrient packages, although rarely is this required for the home gardener.
There are also organic fertilizers that are packaged in a similar way as conventional fertilizers, with the three main nutrients – nitrogen, phosphorus and potassium – along with other minor nutrients. These packaged organic fertilizers can provide nutrients faster than other types of organic materials and so are similar to conventional fertilizers, although not quite as fast-release in nature.
There are also organic materials, such as manures, composts and cover crops, as well as other specific types, such as bone, blood, cottonseed, and fish meals or even grass clippings and leaves. All of these, in appropriate amounts, can be used as fertilizers and provide some nutrients or all three main nutrients. While some of these materials provide fast-release, most are slow- to very slow-release. More importantly, they usually have very low nutrient levels, meaning that substantially more of these materials is required to provide adequate fertilization.
The bottom line is that plants need nutrients, which means at some point you will need to fertilize. Understanding your soil nutrient levels and the materials you are using is critical to having good plant growth. However, regardless of the materials used to fertilize, the tendency is to add more potassium and phosphorus than is required but not enough nitrogen, which is a critical yearly need. Soil testing is a great way to make sure what you truly need for your garden.
Thought for the day: “You can bury a lot of troubles digging in the dirt.” —Author unknown.
For more information about these topics call the Utah State University Extension Grand County office at 259-7558 or email Mike Johnson at mike.johnson@usu.edu.