Root Feeding vs.
Trees have been traditionally fertilized by creating holes
in the root zone and pouring in dry
fertilizer. Some arborists use probes to inject liquid
fertilizer into the root zone area. Some pros also use Mauget
injection, where holes are drilled in the trunk, and fertilizers are introduced using capsules.
Another method is hammering hardened, pointed rods (called "spikes") of fertilizer
into the rootzone.
Recent tests have shown that surface applications of fertilizer, at
the right time of year, can be as effective as deep feeding
methods. These surface apps should be timed for late fall or early
spring, when tree tops are still dormant yet roots are active. Roots
remain active until the soil drops below 40-degrees F and this
period includes several weeks after leaf drop in fall, and a few
weeks before spring bud break. Therefore, these applications would
be considered dormant feedings. Most trees like a 2-1-1 fertilizer
analysis, such as a 20-10-10.
Cyclone spreader for surface application
In the Zone
(..the Root Zone that is)
Placement of fertilizers need to be where the tree can get them, so
don't place them too deep --- most tree
roots are within 12" to 18" of the lawn surface. Tree size and
fertilizer analysis will dictate the exact amount of fertilizer you
should end up applying. To prevent groundwater contamination, don't apply fertilizer when
tree roots aren't actively growing, since this will allow the
nutrients to leach from of the root zone area.
Chemical fertilizers shouldn't be put in the planting hole when
a tree is first planted, since this can cause root burn.
We would recommend using an organic fertilizer -- a slow
release fertilizer with little burn potential -- in with the soil
backfill. Just remember that a "little bit" is always better than too much.
Since it's difficult for phosphorus to move through the soil, this is your best chance to introduce phosphorus. An
organic source of phosphorus used when planting spring bulbs is bone meal. Triple super phosphate (0-46-0) is
a chemical source. Phosphorus promotes rooting, as
well as blossoms, in trees that flower.
Where are the feeder roots?
Below is a
bird's eye view of a tree's root zone illustrating where most of the
"feeder roots" are located. The green line represents the tree's
branch tips, also known as the "drip line." Most feeder roots on a
tree are located just inside, and just outside of the drip line, as
indicated by the zone surrounded by dashed red lines below.
Therefore, focus your tree fertilization efforts in the area between
the two dashed red lines, where most of the feeder roots are
located. (Tree research also indicates most tree roots are located
on the north side of a tree)
Key to Diagram
BLACK = tree trunk and roots
GREEN = tree canopy drip line
RED = Area between the dashed red
lines represents the highest concentration of feeder roots.
Fertilize in this zone.
bags have three numbers on the label, indicating the fertilizer
analysis, or "percentage by weight" of nitrogen, phosphorus and
potassium, in that sequence.
A 50-pound bag of fertilizer labeled 10-5-5 would contain 10%
nitrogen (5 pounds), 5% available phosphates (2.5 pounds), and 5%
soluble potash (2.5 pounds). Here's the math:
50 pounds of 10-5-5 fertilizer:
10% nitrogen (.10 x 50 lbs = 5 lbs)
5% available phosphates (.05 x 50 lbs = 2.5 lbs)
5% water soluble potash (.05 x 50 lbs = 2.5 lbs)
would be considered a "complete" fertilizer since all three nutrients are
present in the bag.
Fertilizers are also rated with "ratios" that indicate the
proportion of nutrients to one another. For example, a 10-5-5
fertilizer is a 2-1-1 ratio, while a 20-10-5 fertilizer is a 4-2-1
A fertilizer ratio of 2-1-1 is what most trees prefer, which translates into a
fertilizer analysis like 20-10-10 or 10-5-5.
FAQ about trees
How mulch is made