What exactly is fertilizer? All plant life, whether it be a tomato plant or a cactus, requires certain elements to aid in growth. In essence, fertilizer is a mixture of nutrients that plants need in order to mature. The three most essential elements needed by plants are nitrogen, phosphorus, and potassium. Nitrogen (N) is vital to the building of chlorophyll in a plant, which allows photosynthesis to take place. Phosphorus (P) is crucial to a plant’s growth, as it helps promote the development of root systems, encourages plants to bear fruit or flowers, and makes plants more resilient to disease. Potassium (K) (often called potash when being used in fertilizer) plays an important role in regulating the amount of water a plant absorbs and expels. Not only do these elements help plants grow to be healthy, but they also help make the plants more nutritious. While these elements are naturally occurring in soil, without fertilizer, the food grown in gardens or farms would not have the same amount of nutritional value that they do now. Furthermore, the nutrients found in soil get depleted after a few cycles of plants have been grown in them, but the use of fertilizer can help in keeping the soil usable for longer.
A lot of commercially available fertilizers found at a garden or home improvement store are a combination of the aforementioned nutrients. What is different between various types of fertilizer is the amount of nitrogen, phosphorus, and potassium found in them—often called the NPK balance. The NPK balance is displayed on the fertilizer’s container and shows what percentage of each nutrient is contained in the soil. So, an NPK of 5-10-5 contains 5% nitrogen, 10% phosphorus, and 5% potash. The NPK balance varies from fertilizer to fertilizer to suit whatever kind of plant you are growing. For instance, leafy greens, like lettuce, Brussels sprouts, or kale, are all plants that require a decent amount of nitrogen, which means you should consider a fertilizer with a NPK balance high in nitrogen. Root vegetables, fruits, and corn thrive best with fertilizers high in phosphorous and potassium. Some fertilizers are marketed as all-purpose, which means that their NPK balance is equal parts nitrogen, phosphorus, and potassium.
Fertilizer should generally be added to soil prior to planting, but it can be added after planting so long as you are using granule fertilizer. Using a liquid fertilizer after you plant your crops runs the risk of damaging or even killing your plants. Some plants, like tomatoes, corn, or squash, can benefit from a fertilizer boost after they have started growing. Overall, it is advisable to look into what nutrients your plants need before you start planting so you can acquire the best kind of fertilizer for your situation. Moreover, it may be worth investing in a soil nutrient test kit, available at most garden supply stores, to get a precise measurement of what nutrients are present in your soil. Average test kits are typically $10 to $30, but you can expect to pay more ($100+) for advanced kits.
Fertilizers are often necessary, but they should be used responsibly. Fertilizer runoff can be damaging to your garden’s surrounding environment, especially if it gets into a storm drain or other water runoff area. You should also be sure to not fertilize your garden when it is windy out, as the fertilizer can be carried by the wind into areas surrounding your garden.
If you are concerned about the environmental impact of manufactured fertilizers, there are more natural options. Manure, which is effectively just animal excrement, is an excellent alternative to store-bought fertilizers. Animal manure contains high levels of nitrogen and is a great way to enrich your soil prior to planting. Not all animal waste can be used as manure, but cows, horses, sheep, and poultry are all great sources. You will want to mix the manure into your soil. If the manure is left lying on top of the soil, it will likely evaporate into the air, making the manure essentially useless. When tilled into the soil properly, manure not only promotes the growth of your plants, but it also helps improve the quality of your soil in the long run. Compost, bone meal, grass clippings, and coffee grounds are just a few other great additives to improve your soil in the long run. The downside to using manure as your fertilizer is that you cannot as precisely control the amount of nutrients going into the soil. On top of that, there is not as much phosphorous or potash in most animal manures compared to chemically produced fertilizers.
Enriching your soil with fertilizers is a necessary step to take in order to have a healthy garden. There is nothing but options when it comes to fertilizers from store-bought fertilizers containing precise NPK percentages to good old-fashioned manure. Every garden has different needs depending on its surrounding environment and soil condition. Understanding how fertilizer works and how to differentiate between various types of fertilizer is a great first step at making your garden as prosperous as possible. 
Andy Baker
Home & Yard Magazine
