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This unusually
warm and dry season has extended outdoor gardening activity, allowing
for tree planting, pruning, and watering to continue unabated. Tree
planting in fall is always a good idea for several reasons: trees will
establish roots until the ground freezes. and late in the season, prices
drop on nursery stock. We will examine some common landscape trees that
can be thriving additions to your landscape, beginning with the popular
birch trees.
Birch trees are prized for their outstanding bark characteristics and
delicate foliage. Almost all landscape cultivars are distinctive in
bark coloration, growth form, and susceptibility to certain insect pests.
Homeowners often desire birch as an ornamental tree, but can discover
that without proper care, birch can be difficult to maintain as a healthy,
long-lived specimen. Many landscape birch trees begin to decline within
a few years, and often die before reaching maturity. A healthy birch
tree should survive and thrive for 40-50 years. However, it is not unusual
for birch trees, especially the white-barked birches, to die well before
reaching 20 years of age.
In many instances, homeowners have predisposed their birch trees to
problems by planting and growing them under conditions that are not
the best for their survival. Following some simple guidelines saves
trouble later.
•Select an appropriate location for your birch tree.
•Select the most appropriate variety of birch.
•Follow cultural practices to maintain a healthy tree.
•Control common insect pests of birch trees.
Selecting
the Proper Site
In the forest, birch trees thrive in cool, moist soils. A shallow root
system makes them sensitive to even short periods of drought or heating
of the soil, they grow poorly in hot, dry soils. Place birch trees in
locations where the soil will be shaded, cool, and moist. However, birch
trees require full to partial sunshine on their leaves to grow well.
The challenge is to select a growing site where the soil will remain
cool and moist, but where the tree will also receive full sunshine on
its leaves for much of the day.
Excellent locations for birch trees in the landscape generally are found
on the east and north sides of a home where the building provides afternoon
shade. Avoid southern and western exposures where the afternoon sun
heats and dries the soil. Existing trees and structures can often provide
the necessary shading. The best time to evaluate your landscape for
a proper site is mid to late afternoon. Look for locations where the
ground is shaded. Another common mistake is planting young trees under
overhead wires. Birch trees growing in yards can reach 40-50 feet in
height. Avoid areas where the soil is compacted or likely to become
compacted, such as along trails or driveways. The shallow root system
can be easily damaged by soil disturbance. Compaction can be lessened
by mulching and/or soil amendment.
Selecting
the Right Birch for Your Landscape
A number of different types of birch trees are available for landscape
use. Most have common characteristics such as size, with a mature height
of 40-50 feet in height. Birches are available as single stemmed trees
and as clumps having 3-5 stems.
The white-barked birch trees are more susceptible to attacks by bronze
birch borer, a serious insect pest, than species without white bark
(river birch, Heritage river birch, sweet birch, and yellow birch).
Whitespire birch is one exotic white-barked birch tree that has been
more resistant to bronze birch borer than the other exotic trees, thought
it is still susceptible. In our climate, river birch or Heritage river
birch is a better tree selection than the white-barked trees.
Maintaining
Your Tree
Cultural practices (mulching, watering, fertilizing and pruning) play
an important role in developing and maintaining healthy birch trees.
Mulching and proper watering are the most important practices that can
create the cool, moist soil conditions that birch trees need. Aside
from aesthetic benefits, mulching moderates soil temperatures, conserves
water in the soil, adds organic matter to the soil, and reduces soil
compaction. Decomposition helps build new layers of soil which aids
in better water retention and oxygen exchange. Mulch around the base
of a tree also reduces the likelihood of damage from lawnmowers or weed
trimmers.
The best
materials for mulching are wood chips, shredded bark, and leaf compost.
Crushed or washed river stone is probably the best material if rock
or stone mulch is your desired choice. Do not place plastic under any
of the mulches since it can retard water movement and oxygen diffusion
into the soil. Mulch should cover a radius of 6 feet for mature trees
and 3 feet for newly planted trees as shown in the diagram above.
Sufficient water is probably the single most important factor in maintaining
a healthy birch tree. If rainfall is insufficient, supplemental watering
may become necessary. During the growing season a slow (2-3 hours),
deep (8-18 inches) watering once per week is a general rule for maintaining
adequate soil moisture. Infrequent, light waterings are not recommended.
Laying a hose on the ground and allowing it to run slowly over the root
zone is a very good technique for ensuring adequate watering. A soil
that can be formed into a ball in your hand has sufficient moisture;
loose, dry soil that crumbles in your hand indicates the need for additional
watering. Watering should be decreased by late August to allow for proper
winterization of a tree.
Fertilization is beneficial only when nutrients are lacking. If a tree
is showing stress symptoms that are not the result of insufficient nutrients,
fertilization will not correct the problem. The reasons to fertilize
are to correct a nutrient deficiency, to accelerate growth when trying
to establish a new planting quickly and to maintain health (usually
to replenish nitrogen). The best time to fertilize is late fall or early
spring. Do not apply fertilizers between mid-August and mid-September
as that may force a late flush of growth that may not harden off before
winter. Nutrients should be available to the tree during its peak growth
period in the spring and early summer. Fertilizers should not be applied
when the ground is frozen. Make sure adequate water is available following
the application of fertilizers.
Excessive pruning should always be avoided. Heavy pruning increases
light penetration to the root zone and can increase soil temperatures
and reduce soil moisture levels. Pruning of birch trees should NOT be
done between May 1 and August 1 as this is the flight period of the
bronze birch borer, and female birch borers are attracted to fresh pruning
wounds. If pruning must be done during this time period, treat the wound
with a registered insecticide. Wound dressings should not be used since
they are not effective at repelling borers and do not promote closing
of wounds. In most cases, regular fertilizer and pesticide application
are best done by a professional tree care company.
Soil testing is provided by The Johnson County Extension Services at
their office in Olathe. Dig down 4-6 inches in 10 - 15 different spots
in the garden or yard and mix this all together. The test is $7.50 and
is available at their office at 13480 South Arapahoe in Olathe.
The Johnson County Extension Office also provides detailed information
discussing tree planting, tree fertilization, and insect and disease
management of shade trees. These publications are available on the Internet
at www.oznet.ksu.edu/johnson.
Robin
Milliken is a Landscape Specialist and Master Gardener
The Master Gardener appears monthly in The Olathe Daily News.
© H&R Lawn and Landscape
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