Tree Nutrition and Fertilization


The stated objective for fertilization with typically fall into 3 categories:

1. Correcting a Nutrient Deficiency.

2. Maintenance fertilization.

3. Growth Promoting Fertilization.

Fertilizer Types: are defined by their chemical composition, form, and mode of action

  • Chemical Composition – Is the analysis of a fertilizer. This simply indicates the elements contained in the fertilizer, and the relative proportions ( % of dry weight) of each element. The percentage of “N” (nitrogen) is always listed first followed by “P” (phosphorus-phosphoric acid P2O5) and then “K” (potassium-soluble potash K2O)
  • Mode of Action (fast-release & slow-release) – regardless of the mode of action the intent of fertilization is to provide essential elements to the tree in a timely manner. Fast release fertilizers are soluble immediately after their applied. Slow release fertilizers are soluble over time in 1 of 3 mechanisms: Biological decomposition of the fertilizer, hydration (water dissolves the fertilizer) or heat. Over all slow release is preferred due to its many benefits; lower concentration of salt therefore less burning of foliage, can be applied in higher concentrations, les prone to leaching losses.
  • Fertilizer Form (organic & inorganic fertilizers) – organic fertilizers are recognized as having been derived from once living organisms (ex. Manure, treated sewage, fish meal, bat guano and compost) inorganic fertilizers are manufactured combinations of minerals and essential elements offered in liquid or dry formulations.

Fertilizer Application Methods: 4 methods of delivering fertilizer to a tree: broadcast application, sub-surface application, trunk injection, and foliar application.

  • Broadcast – fertilization is delivered to the surface of soil in either liquid or dry form. In the rooting zone distributed evenly (good if little or no vegetative understory)
  • Sub-Surface – applied 6-12 inches (15-30cm) beneath the soil in either liquid or dry form. Good if high density of competing understory vegetation. 3ft x 3ft (1m x 1m), beneath the crown of the tree (drip-line), divid equally amongst each hole.
  • Trunk Injection – or capsule implants mostly used to treat micronutrients deficiencies, not a viable method for delivery of macronutrients. Technique is a low volume of product inserted directly into the vascular system (xylem) of the tree. Every 6 inches or 15cm around the circumference of the tree at the base (root flare). Disadvantage it wounds the tree therefore not recommended annually
  • Foliar – if essential elements in the soil are not a soluble form and other methods have weak results then consider this method. Fast-release fertilizers sprayed in liquid form onto leafs surface. Effectiveness determined by the formulation and length of time spent on the leaf. Most successful supplements are calcium, potassium, iron, zinc

Rate of Application: ANSI A300 standards (“N” content)

Maintenance fertilization – 1bls (0.5kg) per 1000ft2 (93m2)

Maximum fertilization fast release – 3bls (1.4kg) per 1000ft2 (93m2)

Slow release – 6bls (2.7kg) per 1000ft2 (93m2)

Growth promoting fertilization – 2bls (0.9kg) per 1000ft2 (93m2)

Timing of Application: When the tree can use it! Best time to apply is just as leaves expand

Prescription Fertilization & Nutrient Management Plan: nutrient management plan should address the “tree(s)” needs based on species, growth phase, health, and soil’s ability to meet annual demands for essential elements. The plan should also identify potential limiting factors for maximum tree health. Remember fertilizer helps trees in many ways, however the misapplication can seriously affect the health and longevity of a tree and have tremendous affects on the environment.