06/23/2021
This post will run a little long but has very valuable information from Dr. John Ball's Alert Bulletin that he publishes every month. It is critical that we start watering ALL our trees, even the mature ones.
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Every tree in the state needs a drink right now. When
temperatures hover in the 90s and low 100s, mature
trees need a good drink about every five days.
Assuming it does not rain during a five-day period,
matures trees may require about 500 gallons of water.
An often cited rule-of-thumb for matures trees – those
more than 10 inches in diameter at 4.5 feet above the
ground – 15 gallons per inch per watering is needed.
This means a 20-inch diameter tree needs about 300
gallons per watering.💦💦💦💦💦
This is a good approximation. The amount of water may
be less than what the tree requires but trees store water
and so do soils. A tree would receive about 900 gallons
over a two-week period following the irrigation rule-of
thumb and a little rain during this same time would
balance it out the 1,500 gallon requirement.
A 1/2-inch garden hose delivers about 10 gallons a
minute, so a lawn sprinkler needs to be on about 30
minutes to deliver 300 gallons. The sprinkler should be
set near the trunk of the tree and then moved a few
times to soak an area equal to about half the height of
the tree. This is the area where the tree’s root density is
the highest.
The watering needs for younger, smaller trees is as
critical but the amount of water needed is less. However,
since they have a smaller trunk and the roots occupy a
smaller volume of soil, they cannot store as much water
so the frequency increases. They need to be watered
about every three days.
Tree seedlings should receive about a quart of water
each watering. Saplings – trees about one to two inches
in diameter at 6 inches above the ground (referred to as
caliper) – need about two gallons each watering. Young
trees, those larger than saplings but less than 10 inches
in diameter at 4.5 feet above the ground need about 5 to
10 gallons per diameter inch each watering.
Tree size Water quantity/watering
Tree seedlings 1 quart
1 inch caliper tree 2 gallons
5 inch diameter tree 50 gallons
20 inch diameter tree 300 gallons
Rules-of-thumbs are only approximations and these
watering recommendations should be compared against
soil moisture levels. After watering, check the moisture in
the soil to a 12-inch depth with a probe. An old screw
driver will work. Push it into the soil and pull it out and
see if it is damp for its entire length. Before watering the
next time, push the probe in and see if the soil is still
moist (note if the ground is so hard the probe cannot be
pushed down, it is dry!). If the probe is still moist
because it rained during the last few days or the ground
is poorly drained, skip the watering.
Most tree owners are not going to water their trees as
much or as frequent as recommended here. Nor are
people likely to monitor the soil moisture before
watering. This is a lot of time and expense but don’t be
surprised if a tree is dropping leaves, wilting or has
discolored needles if it is not being watered properly this
summer.
While trees need watering now, they do not need to be
fertilized. Surprisingly this is a common question. But
trees do not need fertilizer, what they lack is water!
