Trees have more
extensive root systems than other plants. The roots extend
beyond the branch tips and down to a considerable depth, but
nearly all absorbing roots (approx 95% ) are in the top
12"-16" of soil surface. The critical root zone can extend
three times beyond the drip edge.
Nothing does more
to prevent problems and promote improvement than regular
light fertilization. So don't wait for signs of trouble
Nitrogen is the most critical
nutrient, and is also the most rapidly depleted.
Fertilizers should be applied to the root system as a
granular via broadcast or as a soluble liquid
injection within the rhizophere. Our soils, here in
the Hill Country are high alkaline and usually contain
phosphorus and potassium, this combination acts as an
iron and mineral blocker, which can cause iron
chlorosis or other mineral deficiencies. Adding disper
sulfur (in pellet form to facilitate easy application
with a fertilizer spreader) will help lower the soil
pH to a level rendering the insoluble nutrients to a
soluble state. For trees it is best to apply
a nitrogen fertilizer like Ammonium sulfate 21-0-0
with 24% sulfur. Ionate by Hi-Yield is an excellent
iron supplement with a 16% iron and a 10% nitrogen
and with some trace elements. These can be acquired
at your local farm feed store.
fertilizers contain salts which can burn delicate
absorbing roots. Soluble fertilizers release these
salts in a relatively short period of time, increasing
the risk of damage. It is best to apply a slow release
type fertilizer. Water soluble fertilizers, which are
suspended in water for application offer the most
protection from burning. They release nutrients over
time, rather than all at once and they don't readily
Trees and shrubs should be fertilized over the
entire root system, which usually corresponds to the
branch canopy and beyond, approximately one and a half
times the drip edge.
Newly planted trees and
shrubs can be fertilized by working tree fertilizer
into the soil around the plant. For the first six
months a miracle gro type fertilizer is best, as it
will not burn the roots.
Large trees should be fertilized by using a
water based suspension which is injected into the
ground under hydraulic pressure for more effective
dispersion of nutrients throughout the root zone.
Surface broadcast is also very effective and should
be followed by thorough watering for both methods.
Watering after fertilization is important in order
to complete the task you started out to do.
properly with a low profile sprinkler system and
don't be skimpy on the water or over do it either.
Shallow watering will force the roots to grow too
close to the surface and in the heat of our summers,
the roots will dry out and die. This can cause
extensive root damage and sacrifice the overall tree
health. Trees don't like wet feet, but keep in mind
to quench their thirst. Set out a can or bottle and
when you have at least one inch or water showing,
then move on to the next area of application. If you
don't have an automatic watering system and you can
only facilitate a few trees at a time, that is fine
also, just fertilize a few trees and water them as
you can afford your time until the entire task is
done. Trees are very patient and they will reward
you for your kindness. Of course, if you know that
mother nature will help you out and provide the
rain, then you can apply the fertilizer within her
schedule and split the work task.
The trees should have enough
carbohydrate reserve to weather these
conditions. I would recommend a slow release,
preferably organic, fertilizer. Trees under
stressed conditions require a lot of energy to
metabolize nitrogen, whether NH4 or NO3 and then
apply a light sustainable amount, rather than a
heavy application. A good application of
Protium Hydroxide will provide the absolute best
results. This product is not available from any
of your local garden supply stores, but can be
found in your local grocery store, and best of
all, it is found at the end of your garden
hose (it is water) and apply it
liberally, abundantly and, properly, but not
excessively as trees don't like wet feet.
Contact: cell: 830.257.8871
Jim Rediker - Nurseryman - Arborist - TDA Certified
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