TREE PRUNING TIPS
When to Prune
Conifers (pines, spruces, and
firs) may be pruned any time of year, but pruning during the dormant season may
minimize sap and resin flow from cut branches.
Hardwood trees (walnut, mahogany, cherry, oak, teak, etc. ) and shrubs without
showy flowers: prune in the dormant season (late fall or winter) to easily
visualize the structure of the tree, to maximize wound closure in the growing
season after pruning, to reduce the chance of transmitting disease, and to
discourage excessive sap flow from wounds. Recent wounds and the chemical
scents they emit can actually attract insects that spread tree disease. In
particular, wounded elm wood is known to attract bark beetles that harbor
spores of the Dutch elm disease fungus, and open wounds on oaks are known to
attract beetles that spread the oak wilt fungus.
Flowering
trees and shrubs: these should also be
pruned during the dormant season for the same reasons stated above; however, to
preserve the current year's flower crop, prune according to the following
schedule:
·
Trees and shrubs that flower in early spring (redbud, dogwood,
etc.) should be pruned immediately after flowering (flower buds arise the year
before they flush, and will form on the new growth).
·
Many flowering trees are susceptible to fireblight, a bacterial
disease that can be spread by pruning. These trees, including many varieties of
crabapple, hawthorn, pear, mountain ash, flowering quince and pyracantha,
should be pruned during the dormant season.
·
Trees and shrubs that flower in the summer or fall always should
be pruned during the dormant season (flower buds will form on new twigs during
the next growing season, and the flowers will flush normally).
*Dead branches can be removed any time
of the year.
Proper tools are essential for satisfactory pruning. The choice of which tool
to use depends largely on the size of branches to be pruned and the amount of
pruning to be done.
Hand pruners - Generally speaking, the smaller a branch is
when pruned, the sooner the wound created will seal. Hand pruners are used to
prune small branches (under 2.5 cm diameter) and many different kinds are
available. Hand pruners can be grouped into by-pass or anvil styles based on
the blade configuration. Anvil style pruners have a straight blade that cuts
the branch against a small anvil or block as the handles are squeezed. By-pass
pruners use a curved cutting blade that slides past a broader lower blade, much
like a scissors. To prevent unnecessary tearing or crushing of tissues, it is
best to use a by-pass style pruner.
Pruning saws - Slightly larger branches that cannot be cut
with a hand pruner may be cut with small pruning saws (up to 10 cm) or lopping
shears (up to 7 cm diameter) with larger cutting surfaces and greater leverage.
Lopping shears are also available in by-pass and anvil styles.
Pruning saws differ greatly in handle styles, the length and shape of the
blade, and the layout and type of teeth. Unlike most other saws, pruning saws are often
designed to cut on the "pull-stroke."
Chain saws - Chain saws are
preferred when pruning branches larger than about 10 cm. Chainsaws should be
used only by qualified individuals. To avoid the need to cut branches greater
than 10 cm diameter, prune when branches are small.
Pole pruners - Pole pruners must be
used to cut branches beyond reach. Generally, pruning heads can cut branches up
to 4.4 cm diameter and are available in the by-pass and anvil styles.
Once
again, the by-pass type is preferred. For cutting larger branches, saw blades
can be fastened directly to the pruning head, or a separate saw head can be
purchased. Because of the danger of electrocution, pole pruners should not be
used near utility lines except by qualified utility line clearance personnel.
Tools
should be clean and sanitized as well as sharp. Although sanitizing tools may be
inconvenient and seldom practiced, doing so may prevent the spread of disease
from infected to healthy trees on contaminated tools. The need for sanitizing
tools can be greatly reduced by pruning during the dormant season. If sanitizing is necessary it should be
practiced as follows: Before each branch is cut, sanitize pruning tools with
either 70% denatured alcohol, or with liquid household bleach diluted 1 to 9
with water (1 part bleach, 9 parts water). Tools should be immersed in the
solution, preferably for 1-2 minutes, and wood particles should be wiped from
all cutting surfaces. Bleach is corrosive to metal surfaces, so tools should be
thoroughly cleaned with soap and water after each use.
Tree
sap, gums, and resins are the natural means by which trees combat invasion by
pathogens. Although unsightly, sap flow from pruning wounds is not generally
harmful; however, excessive "bleeding" can weaken trees.
When
oaks or elms are wounded during a critical time of year (usually spring for
oaks, or throughout the growing season for elms) -- either from storms, other
unforeseen mechanical wounds, or from necessary branch removals -- some type of
wound dressing should be applied to the wound. Do this immediately after the
wound is created. In most other instances, wound dressings are unnecessary, and
may even be detrimental. Wound dressings will not stop decay or cure infectious
diseases. They may actually interfere with the protective benefits of tree gums
and resins, and prevent wound surfaces from closing as quickly as they might
under natural conditions. The only benefit of wound dressings is to prevent
introduction of pathogens in the specific cases of Dutch elm disease and oak
wilt.
Types of
pruning
Crown thinning, primarily for hardwoods, is the selective
removal of branches to increase light penetration and air movement throughout
the crown of a tree.
Crown thinning - branches
to be removed are shaded in blue; pruning cuts should be made
at the red lines. No more
than one-fourth of the living branches should be removed at one time.
Branches with strong
U-shaped angles of attachment should be retained and branches with
narrow, V-shaped angles
of attachment often form included bark
and should be removed.
Crown raising is the practice of removing branches from the
bottom of the crown of a tree to provide clearance for pedestrians, vehicles,
buildings, lines of site, or to develop a clear stem for timber production. For
street trees the minimum clearance is often specified by municipal ordinance.
Crown raising - branches to be removed are shaded in blue; pruning cuts should
be made where
indicated with red lines.
The ratio of live crown to total tree height should be at least two-thirds.
Crown reduction is most often used when a tree has grown too
large for its permitted space. This method is preferred to topping because it
results in a more natural appearance, increases the time before pruning is
needed again, and minimizes stress.
Crown reduction -
branches to be removed are shaded in blue; pruning cuts should
be made where indicated
with red lines. To prevent branch dieback, cuts should be
made at lateral branches that
are at least one-third the diameter of the stem at their union.