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Planting
- When choosing trees, it is important to know that the cute one-foot sapling
you purchased will grow to a mature tree over time, although not necessarily
to the size of specimens in irrigated Tucson parks. Look around your town, and
you can find tree monsters that have overtaken houses and yards.
There are many low-water landscape trees that will grow less than 40 feet
high in Oracle. For information on these, see the
Landscape Tree Summary Page.
- When digging holes for trees, you must learn if the species of tree you are
planting grows a taproot. If it does not, dig the hole just deep enough so
that the crown of the root ball is one inch above the surrounding soil and
five times as wide as the root ball. Refill the hole with unamended native soil
unless it needs a soil type very different than our neutral to slightly alkaline desert soil.
If the tree does have a taproot, the hole must be dug deep to remove
decomposing granite and rock that may thwart deep roots. At the same time,
the root ball must not settle so that the root crown is below the soil line.
Dig the center of the hole just deep enough so that the root ball crown is
one inch above the surrounding soil.
Then dig a deep trench around the center so the entire hole is five times
wider than the root ball. Back fill the trench with dirt, place the root ball
on the center, and back fill with the remaining dirt.
Water thoroughly. The wide hole will hold more of our sparse rainwater
and reduce irrigation frequency.
- Check stakes on newly-planted trees for trunk movement. A slight sway
is necessary to develop a strong trunk and roots. After one year, remove
the stakes. Some trees do not need stakes at all.
- To determine how far apart trees should be planted, look up the maximum
width a given tree species is likely to attain. The distance any two trees
should be kept apart equals the sum of the maximum widths of the two trees
divided by two. For example, a 'Desert Museum' variety Palo Verde can grow
to 20 feet wide, and a Western Redbud to 18 feet. Twenty plus 18 divided by
two equals 19 feet separation. When the saplings are small, this distance
will seem too far. Plant shrubs, not trees, to fill in the space. The shrubs
that will be the smallest when full grown are the ones to plant closest to
the trees.
- As a firewise precaution, the closest tip of any tree branch should be
at least 30 feet from your house. Add the maximum width the tree can grow,
divided by two, to 30 feet. That is the distance the tree trunk should be
planted from your house. All tree trunks should be at least 40 to 60 feet
away from any structure.
Watering
- During the warm season, deep-water established trees once a month
to keep them healthy. Many insect and disease problems are caused
by insufficient water. Trees in place less than two years may need
weekly watering depending upon the species. Keep track of soaking rains
on your calendar. You can omit watering within three weeks of a soaking
rain that lasts many hours. Many monsoon rains happen too fast to soak
in and do not deeply water the soil.
- Water landscape trees out around the drip line (farthest extent of
the branches), not at the trunk. This will encourage roots to grow out
and better support the trunk against strong winds. Also, the water will
soften up the ground and allow the roots to penetrate more easily.
If the leafy crown of a tree is 16' in diameter, you will need a 50'
soaker hose to lay around the circumference of the drip line.
If water runs away from your soaker hose, dig a shallow, level trench
under the drip line and lay the hose in it.
Run the soaker hose for one to three hours until the ground is soaked
three feet down. Poke an iron rod with a handle into the ground to
measure the water penetration depth. Allow the soil to dry out between
waterings.
- Fruit trees need more water than landscape trees when bearing fruit.
Build a dirt dike outside the drip line of the tree. Flood the entire
root zone under the leaf canopy with water, and soak the soil to a 3' depth.
Allow the soil to dry out between waterings. Most fruit trees will need
soaking in this manner once a week. Avoid getting water on trunks or leaves.
- Use 2" of mulch for newly-planted trees to conserve moisture.
Keep the mulch 2" to 4" away from the trunk.
- Trees with invasive roots such as California Pepper Tree, Mesquite,
Robinia (locust), and Western Cottonwood should be watered beyond the
drip line after the first year. After two years in the ground, it is
better not to water them (Western Cottonwood is a possible exception).
Their invasive roots will travel far beyond the drip line to find rainwater
wherever it settles. Keep these trees far away from septic systems, sewer
and water pipes. Far away means more than 50 feet, except for Western
Cottonwood: 150 feet.
- Some trees will grow slowly with little water but faster when watered
weekly or every two weeks. Desert Willow grows quickly with extra water
to 30' high.
Tree of Heaven should not be watered after one year and should be located
in a very dry area. It will grow quickly anyway. Arizona Rosewood does not
seem to respond to extra water, but its faster-growing evergreen cousin,
Vauquelinia Corymbosa, may. When a tree is close to its desired height,
taper off watering to once a month during the warm season.
- Finally, trees that have established themselves in the wild probably do not
need your help. Even though they may seem too crowded, or in the wrong place,
let them be. They may be near a low-lying area where rainwater collects.
If they seem drought-stressed and are desirable trees, however, consider
deep soaking in May to break the spring drought.
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Acacia constricta: Whitethorn Acacia
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