Whether you have a new, young tree that has recently been planted or more established trees, the best time to fertilize them is late April or early May.

The main reason that you want to fertilize your trees is to bolster their health, encourage new growth and develop a strong root system to fight off pests, disease, and environmental stresses. Young trees with a trunk diameter of less than 6 inches can especially benefit from regular applications of fertilizer.

While fertilizing will help new or more established trees to develop a strong core system, it can’t solve all of the problems a tree may encounter. However, fertilizing will certainly go a long way in giving your newly planted trees, or established trees, a fighting chance to flourish.

Natural Habitat

When trees grow in their natural habitat, they’re usually supplied with all of the minerals and nutrients they need to grow and survive. In a non-natural habitat, like your front or backyard property, anything that you can do to mimic a natural environment will help the tree to flourish. This may involve leaving leaves on the ground to decompose back into the soil, but chances are that despite your best efforts, the need to fertilize will still exist.

Young Trees

When you have newly planted or young trees, they literally soak up nitrogen from fertilizer, which helps them to grow quickly and establish a dense canopy right into the fall. The tree root system can extend for a long distance over time and the tree continues to absorb nutrients when the area around them is fertilized. As the young tree matures, their roots develop an association with fungi called mycorrhizae that helps the tree utilize minerals in the soil. This association is extremely beneficial because most young trees average about 12 to 18 inches of new shoot growth yearly.


Since trees require nutrients to live and thrive, soil that is deficient in one or more nutrients required for the tree to reach its full potential will be more susceptible to disease, insect problems, and shorter life than a similar, well-fertilized tree. A word of caution is that you should always test your soil for nutrient excesses or deficiencies before applying soil additives because over-fertilization has adverse effects on trees.

According to the Agriculture Department of the University of Minnesota tree-fertilization-guide, the nutrients required by all plants, including trees, is divided into two groups:

  • Macronutrients: 

    Are required by plants in larger quantities than micronutrients. The macronutrients required by plants for growth include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). The addition of macronutrients, especially nitrogen, can result in improved growth while deficiencies can lead to slower growth and visible symptoms.

  • Micronutrients: 

    Are required in very small amounts, include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), chlorine (Cl), and molybdenum (Mo).

Many of the products that you find at your favorite garden center provide trees with the appropriate nutrients and all fertilizer labels indicate the amount of nitrogen, phosphorus, and potassium contained in the product by percent.

How to Determine the Need to Fertilize

Trees in cities and suburbs are often stressed due to low moisture availability, soil compaction, physical damage, nearby construction, and competition from turf, nearby trees and shrubs. While fertilizing may reduce environmental stresses, it cannot eliminate them entirely. Therefore, newly planted trees should be watered and pruned regularly to keep weeds away from their bases to avoid excess stress.

A Final Note

The history of the yard can be a final indicator of the need for fertilization since trees in regularly fertilized yards for turf rarely need to have supplemental fertilizer applied. The need to fertilize a newly planted or more mature tree should only be considered if shoot growth is less than 2 inches or soil testing reveals a specific nutrient deficiency.

Testing tree fertilizer or planting a new tree can be troublesome. Depending on your tree species, too much, or the wrong type of tree fertilizer could kill it.  Contact our Burlington landscaping company today and we’ll be ready to help with all your lawn and landscaping needs.