Why Fertilize Your Trees

McFarland’s Arborists generally recommend fertilizing trees in the fall. When discussing fertilization with our clients, we have found three questions reoccur. Here are those questions and our answers to them:

Q. Why is it necessary to fertilize my trees when it appears the ones growing in a forest environment seem healthy without it?

A. Trees growing in designed landscape settings are not the same as those growing in a forest. Leaves and debris that fall from forest trees remain there. Breakdown of these materials creates a less compact and more nutrient-rich soil that is rarely reproduced in the average yard.

Leaves in yards are usually raked up and hauled away. Ground covers (ivy, pachysandra, etc.) and grass (the worst of all) are in competition with tree roots. Therefore, your trees must work much harder to get the water, oxygen and nutrients they need.

When you walk through a forest, you may notice many trees which are dying. Typically, that is not a problem because other trees will fill in and replace those that die. However, in your yard which has a limited number of trees and space, losing even one tree can be devastating to your landscape.

Q. Doesn’t fertilizing just make my trees grow faster and therefore accelerate the need to prune?

A. If your trees are growing more, they are healthier. Using a slow-release fertilizer in the late Fall, we create a gradual breakdown of nutrients, encouraging root growth over the winter and some new growth the following Spring. This is the optimum method of fertilizing trees and comes closest to the way trees feed themselves in the forest.

In most cases, pruning trees more often is less expensive than removing and replacing them when they die. Who wants to wait 20 years for the new trees to grow?

Q. Will fertilizing burn trees already stressed due to this summer’s drought?

A. The fertilizers we use do not burn trees. They release Nitrogen and the other necessary nutrients slowly into the soil over the course of the entire year. In fact, the extended drought over recent years is another reason to fertilize. When trees are stressed due to drought, their roots die.

Fertilizing encourages root regeneration, helping trees cope with drought stress in the future. Stressed trees are more susceptible to insect and disease problems that are killing so many of our trees in the Philadelphia region.

Providing adequate nutrients keeps trees healthy longer, and helps them not to succumb to problems as they age.


Mulch comes in various forms. Here to assist you are the main options and their pros and cons frpm McFarland Tree Service:


Wood chips are a good choice for mulching paths or areas with a lot of ground to cover. Chips often can be obtained for free from tree and utility companies, arborists, and municipal yard-waste facilities. Wood mulches should not be used in garden beds or locations near the house due to termites and other destructive insects that may be living in them. A popular low-cost choice for wood chip mulch is made from construction wastes and wood pallets, however they should not be used in vegetable gardens due to possible industrial contaminants.


Typically sold as shredded pieces, bark decomposes slowly but stays in place. Options include hardwood or softwood. Common hardwood types include hickory, oak, and elm. Softwood bark, such as pine, fir and redwood, decompose more slowly than hardwood. For garden beds with perennials and shrubs, or where you don’t turn the soil often, you can use mulch materials that break down slowly.


Durability is both the appeal and the drawback of stones as mulch. They stay put and don’t degrade, however they do nothing to improve the soil. Stones or gravel are best used in paths or around trees and shrubs about one inch deep for weed control and water permeability. During hot weather, stones or rocks can radiate heat and cause extreme temperatures, resulting in water loss and severe plant stress.


If weed control is your goal, shredded leaves are your star, especially in garden beds. Leaves from just about any deciduous tree work well. Contrary to popular belief, leaves such as oak will not acidify the soil. Oak leaves are acidic when they’re fresh, but they lose acidity as they decompose.

Leaves should be coarsely shred or chopped by running over them with a lawn mower to prevent matting or blowing away. When you dig into soil that’s been mulched with leaves, you’ll find lots of plump earthworms—nature’s finest fertilizer for your garden.

GRASS CLIPPINGS Grass clippings are a treat for vegetable, annual, and herb gardens, because you can get them from your own yard (though never use grass that has been treated with herbicide). Grass clippings decompose quickly, especially in very hot weather, so reapply them often. For best results, allow them to dry before spreading. Both leaves and grass should be applied two inches deep and replenished as needed. Grass clippings and shredded leaves provide a natural mulch. They breakdown much more quickly than bark or wood chips and offer more nutrients to the soil.


When you dig into soil that’s been mulched with leaves, you’ll find lots of plump earthworms—nature’s finest fertilizer for your garden. Spring is the best time for mulching trees, shrubs and planting beds when Landscaping. Mulching offers many benefits, including weed control, retention of soil moisture, and improvement of the overall aesthetics of the landscape. Mulch helps maintain uniform soil temperatures, minimizing damage during drought conditions in summer and root freeze in winter.

Fertilizing in Urban Landscapes

Why fertilize trees in urban and suburban landscape? In a forest—trees’ natural environment—trees self-feed through the natural process of leaf drop and dead wood decaying on a thick, nutrient-rich floor. In urban and suburban settings, the absence of this natural litter, diminishes the ability of trees to fight insects and disease. These settings also bring other stress factors, such as a higher average heat index, soil compaction due to sidewalks and parking lots, and pollutants, including winter’s excessive road salts. When a tree is out of its natural environment, we must take responsibility for its care and pick up where Mother Nature left off. Our job as arborists is to mirror nature as closely as possible by restoring the balance as best we can. Through a non-spray, sub-surface, fall fertilization program, administered periodically, nutrients are injected into the soil to encourage the root system’s ability for nutrient uptake which fortifies a tree’s ability to withstand stress.