Jomar Logo

4 Different Tree Fertilization Techniques

Trees in the forest thrive without the addition of fertilizer. Forest soils are rich in humus, which is replenished by the decay of plant and animal residues. Leaves are relatively high in accumulated nutrients and their decomposition is an important source of returning nutrients to the soil.
In contrast, domestic and urban areas are usually very low in humus and fertility. Leaves and other debris are removed, thus interrupting nature's recycling program for nutrients and preventing the accumulation of organic matter. Shade and ornamental trees in the urban forest require supplemental nutrients for optimum growth and development.

Landscape and urban trees typically grow in soils that do not contain sufficient elements due to disruption of the nutrient cycle by pavement, buildings, turf, granite cover and roads.  Also, leaves, the driver of the nutrient cycle, are raked up before decomposing and micro-organism's break stuff down. Soil in the valley is generally alkaline, or high pH, and therefore 'traps' micro nutrients and prevent their uptake by the trees.

The key to tree fertilization is distributing the right type and the right amount of nutrients at the right time.  Macro-nutrients are nutrients that trees need the most and is frequently deficient in a tree.

Signs your tree is nutrient deficient...
 reduced growth, smaller leaves and the yellowing of leaves.

Secondary nutrients or nutrients needed in moderate amounts include phosphorus, potassium and sulfur. Micronutrients are nutrients that trees need in small amounts include iron, manganese, zinc, copper, boron, silicon, and molybdenum.

Many times it can be hard to tell what nutrient is deficient as the symptoms may overlap. However, it is worth finding out as you may be wasting fertilizer on a tree that needs different treatment.  If you see leaf discoloration or other unhealthy signs on the bark, call me at the number on this page of click HERE to send an email, to get an idea of what might be wrong.

Tree fertilization application techniques vary based on the foliage,  tree condition, the time of year and your preference for using "greener" techniques.

In order of ease to apply:

1. Surface Application
Easy application with ok results

A granular fertilizer is broadcast over the ground surface using a spreader.

The advantage is it's ease, with very little special equipment required.
The disadvantage is lots of residual chemicals on your lawn; washes off into storm drains and subsequently into the water supply; fertilizer leaches through the soil quickly and moves past the root zone where it is not available to the tree. And sitting in sunlight will oxidize the fertilizer and reduce it's potency.

Best Method 2. Sub-surface Application
Harder application with best results

Sub-surface fertilization techniques are necessary when a tree is surrounded by turf or to limit chemical exposure. Turf grass absorbs nutrients more readily than tree root systems so the fertilizer must be applied below turf level.  Subsurface fertilization techniques are also necessary where runoff water is common. Two common techniques are drill hole and injection.

The drill hole method involves drilling holes around the tree in concentric circles. Holes should extend to the drip line. This allows you to put fertilizer deep enough that turf grass won't reach it but shallow enough so it doesn't leach (drain away) especially during the rainy months.

Liquid injection uses fertilizer, dissolved or suspended in water. The solution is injected into the soil using a soil injection system, deep root feeding. This is necessary when a tree is surrounded by turf, granite cover, concrete, pavement or other surface which covers the ground beneath a tree.

Here's Why...Advantages of Deep Root Feeding
  1. Better fertilizer distribution.
  2. Nutrients added directly to the feeder roots.
  3. Better nutrient to root contact.
  4. Adding water directly into the root zone.
  5. No runoff after over-watering or rain.
  6. Slow release fertilizer stays put for up to two years
  7. Soil fracturing to promote oxygen diffusion and aeration.
  8. Reduced or eliminated surface burn.

Pressurized liquid soil injection is the most effective method of distributing nutrients throughout the root zone of woody plants.

Pressurized Liquid Injection -

A soil injection probe with lateral ports results in a distribution pattern that radiates from the probe much like the spokes of the wheel as the probe is pushed into the soil. The ideal injection depth is from 4 - 12 inches, which distributes the nutrients below the majority of turfgrass roots that compete with a tree roots for the growth factors in the soil. This depth is also below the harsh surface conditions that can kill the roots of woody plants. In addition to nutrient distribution, pressurized water creates horizontal capillaries that allow oxygen to diffuse lower into the soil, supporting a deeper, healthier root system. Therefore, this process is fertilization and aeration.

Fertilizer Placement -
Although roots may extend beyond the dripline, fertilizer is generally distributed throughout the area covered by the branch spread. The greatest concentration of nutrient absorbing roots occur in this area.

Fertilizer is injected into the root zone to a depth of 4 - 12 inches. Injections are spaced ~3 feet apart throughout the branch spread area. Pressure at 150 to 200 psi using an injection probe with four lateral ports forces the soluble and suspended nutrients laterally through the soil, providing better nutrient to root contact.

Deep Root Feeding Injection Spacing Diagram
Each dot represents an injection site beneath the canopy of the tree

deep root feeding spacing diagram

Example of exposed root system

Tree on left un-treated
Tree on right treated

3. Foliar Application
Hardest specific application with individualized results

Foliar application is a short term fix to correct minor elemental deficiencies of micro nutrients. Typically spraying the leaves works best in spring, right before a period of active growth.  This procedure is not generally accepted as a practical method of fertilization.

4. Systemic Tree Injection
Hardest application with teriffic results

Systemic tree injections are generally used for minor nutrient deficiencies, fungal and pest control. Tree injections provide a systemic application and can be combined with insect and fungal control. Systemic injections enter the plant via the trunk and pass internally through the tissues.
The main advantage is that it completely eliminates any residue or spillage outside of the tree.

However, because it involves creating small holes in the tree it is usualy limited to a once a year and the trees have to be large enough to handle it. We always look to see if a tree is water stressed before doing this, and combine required soil analysis and ferilization prior to application.

Finally, trees may not require additional fertilization at all. Over fertilization can burn out leaves or cause a tree to grow too quickly resulting in frequent pruning or even removal.

Call today and Jomar Tree Service will evaluate your trees for free. If there is a suspected problem, we will bring it to your attention and advise accordingly.

Don't forget about our Veterans Discount...

Jomar Tree Service • P.O. Box 4803 • Cave Creek, AZ • 85327 – serving the Phoenix metro area – 602-285-0285