Plants get most of the nutrients they need to make their food from the soil. While fertile soil generally has sufficient supplies of the nutrients plants need, over time some of them are depleted by the plants and need replacing. Building soil health by adding lots of organic material maintains its fertility so that only a little fertilizer is needed each year. The proper fertilizer can help replace those depleted nutrients, but in the end, adding organic matter every year is the best way to keep a soil full of all the nutrients needed by your landscape plants.
Unfortunately, in many cases the soil in residential yards and gardens is not naturally fertile, so until its made fertile from added organic matter, it is necessary to add fertilizer to assure a healthy landscape for a few years. If you add no organic matter to your soil, you must use fertilizer every year forever. So the more you do to improve the health and quality of your soil over the years, the less time and money you need to spend in the long run on fertilizers.
In average or poor soils, most plants including grass, shrubs, trees, flowers and vegetables grow better if they receive some fertilizer some time during the growing season. Unfortunately, it is possible to use the wrong type of fertilizer on a particular group of plants, and you can, very easily, fertilize any plant too much. Excessive fertilizing can cause more harm to lawns and gardens than neglecting to feed plants at all. Sick plants should never, never be fertilized!!!!
So here are some guidelines for using and choosing fertilizer.
Three Step Fertilization
No matter what type of plants you are feeding, it is helpful to think about feeding them in three ways, similar to the way we humans take our nourishment.
Main Meal - To maintain a low maintenance landscape, give all your plants (lawn, trees, shrubs, flowers, etc.) a basic main meal once, maybe twice, each year. Some specific ornamental plants may need more than two applications.
Snacks - While optional, you may supplement the main meal with occasional snacks for certain plants if they need an energy boost over the long growing season. Remember, snacks are optional.
Vitamins and Tonics - Finally, to increase your plants' ability to make the most efficient use of the nutrients it receives from the soil and any fertilizers, you may give them some "vitamins" or “tonics” designed for plants. Called “bioactivators”, these products are designed to maximize a plant's growth potential. Vitamins and tonics are definitely optional, but often will in the long run help reduce the future need to fertilize a plant.