If you have rich, loamy soil with a high amount of organic matter you may not need to fertilize your plantings – particularly if they are primarily ornamental trees, shrubs, and perennials. However, if you have depleted soils or grow heavy feeders like blooming annuals or vegetable plants, fertilizers can be the difference between successful and unsuccessful plants.
Identifying the N-P-K Ratio of Your Fertilizer
Nitrogen assists in the development of the vegetative growth of plants. It’s necessary for healthy leaves and stems. Minimal plant growth or pale leaf colors are common indicators of a lack of nitrogen. Too much nitrogen may encourage excess vegetative growth, at the expense of blooms or fruit.
Phosphorus assists in root development, flowering, and fruiting. It also aids in the plant’s ability to resist disease. A phosphorus deficiency increases the likelihood of plant disease.
Potassium is a necessary macronutrient for the proper functioning of all living cells. In plants, it’s a critical component of photosynthesis. Low plant vigor and discoloration or curling leaf tips are symptoms of potassium deficiency. You often see these symptoms on older leaves because plants will deliver accessible potassium to newer growth first.
You typically find an N-P-K ratio on the front of fertilizer packaging. The three numbers represent the percent of each nutrient in the fertilizer, by weight. These numbers alone will not tell you whether it’s quick-release, slow-release, or organic. Expect to see higher numbers on synthetic fertilizers than on organic fertilizers. More on that later.