When planting trees, I’m sure that you’ve come across the issue of whether or not to use fertilizer. The answer to this really depends on what type of tree and what type of soil it is going to be planted in. It is also important to recognize that different types of fertilizer are going to be needed just depending on the species and what nutrients they require as not all plants need the same things. Different nutrients and chemicals become growth limiting factors which can change between plant species. As always it is important to know what your plants need and with fertilizer, this is arguable more important than most other aspects.
To truly understand how and why you should use fertilizer, you have to look at a tree or plant as a micro-ecosystem and not just a single living organism. Just like in humans, there are hundreds of millions of symbiotic relationships happening on the microscopic level that you have to take into account if you want to create an ideal environment for your plants. In soil, microbes and small detritivores are responsible for all the nutrient cycling that trees and other plants rely on to grow and survive. These microbes and detritivores in turn, rely on other nutrients that come from the plants, the environment and other factors. The whole purpose of fertilizer is to support and enrich this symbiotic relationship which results in larger growth for your plants. This makes it very important to use the right type of fertilizer as well as the right amount.
To start with, there are two types of fertilizer, organic and inorganic (chemical) fertilizers. Organic fertilizers are usually less complicated as it is usually pretty balanced in nutrients and are generally more helpful to plants as it can provide soil structure, increase microbes present that produce nutrients needed, buffer against toxicity to plants in the soil (alkalinity, salinity and pesticides) and can suppress diseases or parasites but they do have their downfalls. Nutrient levels in organic fertilizer tend to be way lower so you need more to satisfy the needs of crops if the soil is not good to start with or if there are a lot of crops. It also has a slow nutrient release rate as microbes have to physically break down and release nutrients for the plants to absorb them.
Inorganic fertilizers, on the other hand, are very fast acting and immediately provide nutrients to the plants, can be packed with more nutrients and are generally cheaper to use unless you make your own organic fertilizer. The only problem is in the over application of these pesticides as it can reduce soil health, create pH changes through an overabundance of nitrogen present in the soil, and can destabilize the ecosystem. This makes it really important to understand what type of fertilizer you should use and how much of it before you start using chemical fertilizers.
Most packaged fertilizer will tell you how much to use but choosing the right type can be difficult and confusing to even the most experienced horticulturist. To start with the basics, fertilizer will have three numbers on the front which go from left to right indicating the amount of nitrogen, phosphorus and potassium. These are all common nutrients that trees need which our environment may lack which makes them limiting nutrients. Normally, nitrogen is the biggest limiting nutrient and usually fertilizer will include lots of nitrogen to offset this need, with the other two nutrients being much more dependent on the species of plant being grown and the soil microbes. The best way to find the right fertilizer is to either research what plant you want to grow or to ask the person selling you the fertilizer as they will usually know what type of fertilizer you should get and how much.
So now that you have your fertilizer, how should you apply it? In general, if you have seasonal plants or a garden that needs to be replanted every year, it is a good idea to use organic fertilizer to replenish the soil before planting. This allows the soil to replenish itself in a natural way and limits the amount of chemical fertilizer, if any, you will end up needing to supplement your plants. If you are planting trees instead of seasonal gardens, it is a choice you will have to make depending on how the soil is in the area you wish to plant. If you haven’t planted the tree outside and still currently have it in a pot, it can be a good idea to till the soil with some natural fertilizer so that you will not need to use as much chemical fertilizer later on and by the time the tree is big enough to be planted outside, the soil will be in much better condition than it was before. If you do need to supplement with chemical fertilizer it is extremely important not to use too much. Besides the fact that it can change the pH of the soil, it can make the plant more susceptible to diseases by softening the plant tissue, provide runoff that can ruin other areas nearby and can lead to the soil not being able to hold onto nutrients making the soil essentially dead which causes more problems.
In the end, it is important to understand that fertilizer should act as a way to reproduce the natural environment as much as possible. Too much fertilizer can lead to problems regardless of what type you use so it is really important to understand what you are doing before you start. This can be done with only a little bit of research and advice from various sources and will help to avoid the catastrophe of over or under feeding your plants.