Fertilizer companies advertise their product as plant food. Who would want to starve a plant by withholding food? So, people buy the product. According to the late tree biologist, Dr. Alex Shigo, however, plants make their own food so fertilizer is not plant food.
Good soil is full of minerals, beneficial fungi and bacteria, and chemical elements that are essential for good plant growth. These nutrients and minerals also contribute to the photosynthesis process by which plants make food.
The problem is that much of our soil is not that good. Developers scrape away good top soil at the start of a building project. Some may store it and return it when landscaping the finished site. Others sell it and then truck in soil from somewhere else. As a result, the soil in your yard may not be as nutritious to plants as it should be. Fertilizer replenishes nutrients depleted or missing from the soil.
Plants need three macronutrients: nitrogen, phosphorous and potassium. They also need all or some of these 8 micronutrients in varying amounts: boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Nl) and zinc (Zn).
The percentages by weight of each of the three macronutrients are represented by the three numbers on the front of the package. They are always in the same order – N (nitrogen), P (phosphorous) and K (potassium).
Micronutrients do not get their name from their importance but, rather, from the amount needed. Plants only need tiny amounts of micronutrients. The specific micronutrients and the amount they need vary by plant.
With that explanation, the answer to the title question is that you need to fertilize to replenish soil nutrients. The exact amount and formulation can be determined by a soil test. However, a good rule of thumb is that your lawn needs several fertilizations in spring and at least one in fall. Perennials and shrubs may need fertilization in spring and fall. We usually only fertilize trees in the fall to aid in their final push to manufacture enough food to sustain them through the winter and next spring’s leaf flush.
We apply fertilizer to trees and shrubs in liquid form, using a probe to inject it right into the soil at the root zone. Fertilizer has to be in liquid form for plants to absorb it, and this method places it where the plant can begin absorbing it immediately.
If you have questions about fertilization and your property’s needs, call us to schedule an appointment. One of our plant health professionals will look over your property and give you recommendations specific to your landscape.