How to Fertilize
Fertilizer is not necessarily plant food. It is a blend of nutrients that help the plant to perform its daily functions with less stress. The stimulants in the fertilizer are absorbed through the plant's roots, and then distributed throughout the plant. In order for the nutrients to be absorbed evenly, it is important to spread the fertilizer over the entire root zone area. This area usually extends two to three times the width of the branches. A thin layer of fertilizer should be applied to the top of the soil or mulch and then watered lightly. Too much fertilizer can burn the roots, so err to the side of using less if you are not sure about the quantity of fertilizer your tree needs..
When to Fertilize
Hazelnut trees can produce the majority of the nutrients they need on their own. It is even suggested that these trees not be fertilized until after the first two growing seasons have passed. (A typical tree will grow approximately 18 to 30 inches a year.) When these trees are large enough to need the extra nutrients, they should be fertilized in the spring.
There are two common approaches to fertilizing hazelnut trees. Some professionals state that a slow release 10-10-10 fertilizer be used once a year, in March, after active tree growth has begun. This should stimulate healthy growth throughout the summer.
Others state that fertilization should be divided into two stages: first in March, and then again in June. This is supposed to make more nitrogen (the most important nutrient needed for hazelnut trees) move to the roots and throughout the trunk for storage through the dormant period.
Regardless of which method you choose for your tree, fertilizing should never be done after July. This can stimulate tree growth too late in the season and cause damage when the winter comes.