Before you fertilize, take a look at your trees. If you answered yes to any of these questions, the tree might benefit from fertilization. Despite extensive research about how trees respond to fertilizer, scientists and arborists have not reached specific conclusions regarding what type of fertilizer to use, when to apply it, or how much to apply. Below are some of the most common and agreed-upon recommendations. What type of fertilizer to use If fertilization is needed, nitrogen generally is the key nutrient required.
Nitrogen stimulates new growth and keeps leaves green.
Nitrogen is water-soluble and can be carried deep into the soil beyond the root zone by rain and irrigation. Thus, you might need to apply nitrogen every year when trees are young. Phosphorus and potassium also are essential to tree growth. However, neither is used at the same rate as nitrogen, and most soils contain enough of these nutrients. A laboratory soil test will indicate if either element is needed.