Evergreen trees maintain their foliage throughout the year, including conifers like pines and firs and broadleaf varieties such as holly. Established evergreens generally possess lower nutritional requirements compared to deciduous trees, which must produce entirely new leaves each spring. However, relying solely on natural nutrient cycling is not always feasible in residential landscapes where soil conditions are often less than ideal. Supplemental feeding becomes necessary when the tree’s health or growth rate indicates it is not receiving adequate nutrients from the soil.
Assessing the Need for Supplemental Nutrition
Determining whether an evergreen requires fertilization begins with a visual inspection for signs of deficiency. Slowed or stunted growth, with annual twig extension significantly shorter than expected for the species, suggests a lack of nitrogen or phosphorus. Chlorosis, or the yellowing of needles, is a common indicator of a nutrient problem, pointing toward shortages of nitrogen, iron, or magnesium. Magnesium deficiency often causes older needles to yellow while new growth remains green, whereas iron deficiency typically affects the newest foliage first.
Before applying fertilizer, a soil test is the most reliable diagnostic tool, revealing existing nutrient levels and the soil’s pH. Evergreens generally prefer a slightly acidic soil (optimal pH 6.0 to 7.0); a pH that is too high can prevent the tree from absorbing available nutrients. Newly planted or recently transplanted trees should not be fertilized until they have established their root systems (generally for a full year), and trees under stress from drought or disease should also be left unfed.
Identifying the Optimal Fertilization Window
The most effective time to fertilize evergreen trees is just before or at the beginning of their active growth cycle. This period typically occurs in late winter or early spring, generally from March through May, depending on the regional climate and when the ground thaws. Applying fertilizer at this time ensures nutrients are available to the roots as the tree breaks dormancy and prepares for its flush of new growth, supporting its greatest energy demand for the season.
In some cooler climates, another window is late fall, after the tree has entered dormancy but before the ground freezes solid. Late fall fertilization promotes root growth and nutrient storage rather than stimulating above-ground foliage. The roots continue to grow in cooler temperatures, storing absorbed nutrients to fuel the burst of growth the following spring. Avoid applying fertilizer after mid-July in most regions; stimulating new, tender growth late in the season leaves the tree susceptible to damage from early frost before the wood hardens off.
Choosing the Right Fertilizer Formula
Selecting the appropriate fertilizer involves understanding the NPK ratio: the percentage by weight of Nitrogen (N), Phosphorus (P), and Potassium (K). Evergreens benefit from a balanced formula or one slightly lower in nitrogen, such as a 10-8-15 or 10-10-10 blend. Nitrogen promotes foliage growth, phosphorus supports root development, and potassium aids in overall tree health and disease resistance.
Slow-release granular fertilizers are generally preferred over quick-release liquids for established trees because they provide a steady supply of nutrients over several months, mirroring the tree’s sustained feeding needs. This minimizes the risk of nutrient runoff and reduces the chance of fertilizer burn to the shallow feeder roots. Specific evergreen formulas often include micronutrients like iron and magnesium, which are necessary to correct common issues like chlorosis when a soil test confirms a deficiency.
Proper Application Techniques
The effective delivery of fertilizer depends on placing it where the tree’s fine feeder roots can absorb it. These roots are concentrated around the tree’s drip line—the circular area beneath the outer edge of the branches—and often extend well beyond it. Fertilizer should be broadcast evenly over this entire root zone, starting a few feet away from the trunk to avoid damaging the bark and root crown.
For mature trees, deep root feeding involves placing fertilizer into holes 8 to 12 inches deep, spaced about two feet apart throughout the root zone. A more straightforward method for granular products is to simply spread the fertilizer across the surface and water it in thoroughly. Established evergreens in a natural setting rarely require annual feeding; they often thrive with fertilization only every three to five years, or annually only if a severe nutrient deficiency has been confirmed by testing.