Deep-Root Fertilization is the most effective method to fertilize trees. This process injects water and fertilizer under high pressure 8 to 10 inches below the soil surface, where the feeder roots are. The injections are placed in a grid pattern in and around the tree’s drip line. There are many advantages to fertilizing this way. The high pressure injection forces the water fertilizer mix throughout the root zone, which not only feeds all the roots, but reduces soil compaction and encourages additional root zone aeration. Depending on your plant varieties and their health, this deep root injection fertilizer technique may be suggested at various times throughout the season, although, spring and fall are generally the best.
Even though your trees and shrubs may appear to look healthy today, call us for an analysisand our recommendations on a Deep Root Fertilization program to help keep them healthy and strong for years. Tree roots perform many functions. The primary roots grow down into the soil to provide the anchor to hold the tree upright. Secondary roots branch off and extend radially and horizontally and form the basis of the moisture and nutrient gathering system for the tree. Tertiary roots are the ephemeral absorbing roots eventually branch off into clusters of fine hair like feeder roots. It’s these feeder roots, in conjunction with natural mycorrhizial fungi in the soil that break down the nutrients found in the soil, and begin to transport them with the tree system.
While the primary and secondary roots can be found rather deep in the soil, the tertiary and feeder roots will be relatively close to the soil surface. These roots grow horizontally, to just beyond the outer drip line of the crown or foliage. This is where we concentrate applying fertilizer for the trees to benefit the most. These applications are usually timed for late fall or early spring. It’s important to remember that tree roots remain active year round and the tree will benefit from these fertilizations even though the tree appears dormant. Tree size and fertilizer analysis will dictate the actual amount of fertilizer we apply. To help prevent groundwater contamination, we don’t apply quick release fertilizers when roots aren’t active and nutrients leach out of the root zone.
In forests, trees shade out grass and other plants so the tree’s roots don’t have to compete with roots of other plants. Lawn are a harsher environment for trees. When you drop fertilizer on top of your lawn the grass receives most of the benefits. A different type and method of fertilization is used to fertilize trees than what is used to fertilize lawns, since trees don’t grow the same as grass. For trees, slow release fertilizer is applied directly to the tree roots, below the grass roots. This can be done with special liquid fertilizers injected into the soil or dry fertilizers poured into holes drilled into the root zone of the tree. Trees also respond to fertilizer differently than grass. Over-fertilization can create tree health problems, so the need for fertilization should be determined by measuring annual growth, checking visual symptoms and chemically analyzing the soil or tree leaves. Tree fertilization should be done according to ANSI A300 Part 2 standards for tree fertilization.
A300 is the tree care industry’s standards for tree maintenance. Here’s part of what A300 says about fertilizing trees:
- A soil or foliage analysis should be done to determine what nutrients are missing
- Slow-release fertilizer is preferred
- Fertilizer ratio should be 3:1:1 or 3:1:2, or adjusted for local conditions
- 2 to 4 pounds of nitrogen should be applied per 1000 square feet
- Sub-surface fertilization is preferred when lawn grass is present
- The fertilization area must be known before fertilizing
- Fertilizer holes or injection sites must be evenly spaced in the fertilization area
- Fertilizer must be evenly distributed in the holes or injection sites