How to Deep Root Fertilize a Tree

You can fertilize most plants and young trees by spreading fertilizer over the surface of the soil under the plant. This method works well for young trees with shallow root systems. However, as the trees mature, the roots stretch deep in the soil far below where fertilizer reaches. The best way to fertilize these trees is via a method called deep root fertilizing, which injects the fertilizer deep into the soil directly next to the roots.

Tape measure

String

Soil auger

Drill

18-8-8 granular fertilizer

Water

Topsoil (optional)

Walk to the base of the tree and use a tape measure to measure out 3 feet from the base of the trunk. Draw a line on the ground or lay a piece of string in the location. Repeat the process on each side of the trunk and connect the lines or strings to form a square. Do not drill any holes inside this square to prevent root damage.

Place a 1- to 2-inch diameter soil auger into a drill and set the auger on the ground just outside the 3-foot area. Press the trigger on the drill to dig down into the soil until the auger is 1 to 1 1/2 feet deep.

Remove the auger from the ground and walk out 2 feet from the first hole and drill another identical hole. Repeat the process in a straight line until you reach 2 feet past the end of the tree branches.

Walk back to the base of the tree and begin another line of holes that are 2 feet away from the first line. Continue drilling holes until you have a square grid around the entire tree, with each hole spaced 2 feet apart.

Fill each hole with 2/3 tsp. of an 18-8-8 granular fertilizer. Then water each hole well to begin dissolving the fertilizer.

Refill the holes with the soil that was dug up by the auger, or with additional topsoil if needed.