Pruning in Alberta

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By Stuart C. Tucker, P.Ag.

Published by:

Alberta Agriculture, Food and Rural Development
Information Packaging Centre
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Edmonton, Alberta, Canada T6H 5T6

Production Editor and Cover Photo: Scott Reid
Graphic Designer: John Gillmore
Page Production: Sherrill Strauss

Copyright ° 1984. Her Majesty the Queen in Right of Alberta.

All rights reserved.

No part of this publication may be reproduced, stored in a retrieval
system or transmitted in any form or by any means, electronic,
mechanical, photocopying, recording or otherwise without written
permission from Alberta Agriculture, Food and Rural
Development.

ISBN 0-7732-6163-X

Printed in Canada

Contents

Pruning Tools 1

Plant Terms to Know 4

Basic Principles of Pruning 6

Pruning Techniques 7

Pruning Deciduous Ornamental Trees 8

Deciduous Tree Recommendations 11

Poplars, Willows 11

Ash, Elm 11

Crabapple, Mountain Ash, Prunus Species 11

Birch 11

Bur Oak 12

Maple 13

Larch 13

Pruning Evergreen Trees 13

Pruning Shrubs 14

Shrub Recommendations 15

Early Flowering Shrubs 15

Late Flowering Shrubs 16

Foliage and Stem Colour Shrubs 16

Evergreen Shrubs 16

Hedges 17

Pruning Roses 17

Rules of Thumb for Pruning Roses 18

Pruning Fruit Trees 19

Apple 20

Plum 21

Apricot 21

Pear 21

Pruning Bush Fruit 21

Raspberries 21

Currants 22

Gooseberries 22

Bush Cherries (Nanking, Korean, Manchurian) 23

Saskatoons 23

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Proper pruning ensures healthy, vigorous plants by balancing
growth, flowering and fruiting. Your efforts to learn the art and
science of pruning will be rewarded. As your pruning skills
improve, your ornamental plants will become more attractive
and your fruit plants more bountiful.

Pruning tools

There are tools designed specifically for pruning. The average
home gardener requires a modest investment in the correct tools for
pruning. You will need three basic tools: the pruning saw, the long
handled lopper, and the hand pruner. Select good quality tools.
Cheaper tools are usually made of inferior materials, and will
probably have a shorter useful life.

Pruning saws dre specially designed with teeth set at wider angles
to allow cutting into green moist wood without binding. The only
tool larger than a hand saw that should be used by an amateur
pruner is some type of power saw for larger branches or whole
trees. This type of work is best left to a professional pruner as it is
both dangerous and requires special methods.

You can cut branches and stems that are smaller than 5 cm
(2 inches) in diameter with a long-handled lopper. Look for a tool
with well-attached handles, scissor-like action, and a rubber
bumper just behind the pivot point. This rubber bumper helps
absorb the shock when you cut through a large branch and prevents
it from being transmitted up your arms and into your shoulders. Cut
branches and stems that are smaller than 2 cm (3/4 inch) with a
hand pruner (also called a secateur).

Many sizes and qualities of long-handled loppers and hand pruners
are available, but there are only two basic designs: the anvil, and
the hook and blade. The hook and blade design is preferred
because it enables you to make a flush cut with little or no crushing
of tissue. The anvil, by design, will not allow flush cuts and causes
some crushing of tissue. Small stubs and crushed tissue can result

in increased healing times, which is detrimental to any healthy
plant. The hook and blade design is a better tool.

Supplementary tools could include hand or powered hedge shears
and a pruning knife. Select shears on the basis of a sharp cutting
edge, the balance of the tool, the weight of the tool (the lighter the
better, because you have to hold shears up for long periods of
time), and the comfort of the tool to you as a user. Pruning knives
can be anything from a small pocketknife to a kitchen paring knife
or a specially designed pruning knife. When selecting a knife look
to see how suitable it is for you and know the quality of the steel
used in the blade. You must keep it sharp at all times because a dull
knife does more damage than good.

Figure 3. Hand pruner (secateur) Figure 4. Pruning knives and shears

Terminal growth 1

Figure 5. The numbered parts are described on the next two pages

Plant terms to know

The illustration of the tree in Figure 5 uses the terms you should

become familiar with. The parts of the tree are marked by numbers

and these are described below.

1. Terminal growth is the uppermost, usually central, growth on a
stem. If this terminal growth is removed (by accident or by
pruning) then the dominance this growth has over the
remaining stem is broken, and another bud or buds will
develop to take its place. This results in unchecked, wild
growth in the remaining part of the stem or branch.

2. The leader is the central, vertical dominant stem of a tree or
shrub. If the leader is cut or broken by accident, then the whole
tree will display an unchecked growth until another stem or
stems take over as a new leader.

3. Terminal buds are those buds that grow at the end of a stem
and produce the terminal growth.

4. Lateral buds are those buds that grow from the sides of a stem
and

5. from which lateral branches develop.

6. Scaffold branches are the main branches of the tree.

7. Secondary branches are branches that grow from the main
scaffold branches.

8. The trunk or main branch is the original shoot from which all
branches arise. Sometimes it is referred to as the central leader.

9. The crown is the top growth of the plant including all scaffold,
secondaries and lateral growth arising from the trunk.

10. The bud-union or graft is the place where a portion of a branch
(scion) of one variety has been joined to the root (stock) of
another, to form one plant. Many fruit trees are grafted.

1 1 . Roots are the underground parts of the plant that serve to
anchor the tree, and take up moisture and nutrients required for
the plant’s survival.

12. Suckers are shoots arising from the root system below or just
at ground level. This term usually refers to unwanted growth
from below the graft.

13. Watersprouts are vigorous vertical shoots that usually arise on
the top surface of main or secondary branches. These sprouts
are usually caused by severe damage or heavy pruning of the
top growth of a tree.

14. A strong crotch is one that is U-shaped and where the branch
is attached to the trunk with a wide angle.

15. A weak crotch is one that is V-shaped and where the branch is
attached to the trunk with a narrow angle. These types of
crotches are prone to wind damage.

16. A branch that grows toward the centre part of a tree or shrub
sooner or later crosses another growing outwards. Damage to
bark can result from the two branches rubbing together; this
usually calls for the removal of the inward growing branch.

17. New wood is a term used for growth put on during the current
season.

18. Wood older than one season is referred to as old wood.

19. Spurs are structures that bear the flowers and fruit. Apple spurs
are short, stubby and thick whereas European plum spurs may
be very long and thin.

20. As a spur grows, it may develop side spurs and become a

branched spur.

21 . When pruning never leave a stub as this could be a site for
infection and may never heal over.

22. Properly pruned branches leave no stub and quickly heal over.

Basic principles of pruning

Each type of tree or shrub requires a slightly different pruning
method. The time of year pruning can be done successfully varies
with the species.

The basic principles of pruning are few and easy to learn. But the
novice, as well as the master pruner, must keep in mind the slight
differences between plant materials before making a pruning cut.

1 . Visualize the shape of the plant at maturity. To do this, you must
first be familiar with the natural growth habit of the plant in
question.

2. Remove dead, damaged and diseased wood.

3. Select the main scaffold branches (if a tree) or the main stems
you want to keep (if a bush) and remove all of the others. This is
an application of the “work from large to small rule” that is
basic to pruning: cut from the largest branch or stem to the
smallest.

4. Do corrective pruning by removing weak crotches, crossed
branches, suckers and watersprouts.

5. Thin out the crown to well-spaced, strong branches or stems,
secondaries and laterals. This promotes a healthier plant by
admitting more air and sunlight into the centre of the crown.

6. Cut back to the branch collar (the swelling where the branch
joins the stem) so as to leave the smallest wound possible.

7. Remember that too much of anything is not always best. This is
particularly true of pruning. You can always prune again next
year.

Pruning techniques

There are four ways to prune: pinching, thinning, heading back and
shearing.

Pinching is the removal of stem tips. This method controls terminal
growth and allows laterals to grow faster.

Thinning is the practice of removing whole branches to open out
the crown. This practice is especially useful in fruit trees as it
allows more fruit to be set on the inside of the tree.

Heading back is commonly practised on flowering shrubs to
encourage thicker growth and more flower buds setting as a result.
Removing the terminal growth and some of the laterals helps to
create a more compact, strongly branched tree or shrub.

Shearing is practised on hedges and to shape specimen trees. It
involves cutting back evenly all exposed areas of a shrub or tree to
gain the desired effect. Topiary is the practice of shearing trees to
direct their growth in an artistic way.

All four pruning techniques are used when pruning woody plant
material.

Figure 6.

Figure 6. continued

Heading back

Continued thinning with no
heading back

Repeated heading back with
no thinning

Shearing Topiary

Pruning deciduous
ornamental trees

Prune trees from an early stage in their growth. This is when a
good basic tree form can be created. Early, light pruning is
inexpensive and results in a stronger healthier tree. The best time
of year to prune depends on the species being pruned and its
intended use in the landscape. Prune trees grown mainly for their
foliage from late March to mid- April. But don’t prune birch and
maple trees this early. These two species have a tremendous sap
flow until their first leaves have fully opened. Wait until mid-June
to prune birch and maple.

Generally, ornamental trees are planted where their mature size can
be accommodated. If this has been done, only minimal, corrective
type pruning needs to be applied to the tree as it grows. Sometimes
large limbs are damaged or grow in a direction necessitating their
removal. A four-step cutting procedure should be followed to
remove large, heavy limbs. Finish all large cuts by paring the cut
edge smooth. Figure 7 shows this procedure.

Figure 7A. Correct way to remove a branch in four steps - leaving the
branch collar intact

The angle of the pruning cut is also important. Always cut back to a
bud that faces the outside of the tree. This way you reduce the
possibility of crossing branches and too thick a crown. Determine
the correct angle by placing the pruning tool so that the top of the
cut is slightly above the top of the bud and the bottom of the cut is
even with the bottom of the bud.

Figure 8. Correct pruning angle on small branches

Too far above bud Too close to bud Too angled

Correct

Remember to cut cleanly and leave no stub. The correct positioning
of the pruning tool is important when doing this.

Figure 9. Correct positioning of a pruning tool for a flush cut

Correct Incorrect Correct Incorrect

Pollarding results in very unsightly and weakened growth. It is not
recommended. This kind of pruning becomes necessary when trees
are planted in areas where there is not room for them to develop. It
is also practised in areas where trees might interfere with power
lines and pose a hazard. This type of pruning has to be done every
couple of years, so it is usually very expensive. The best way to
reduce pruning maintenance costs is to plant trees that do not grow
as high as the power lines.

Figure 10. Natural growth compared to growth of a pollarded tree

Deciduous tree
recommendations

Poplars, willows

Plant these large, fast-growing trees in areas that allow adequate
space for growth. If you are growing willows for their colourful
bark, give them a heavy pruning to encourage new, more colourful
wood. Do not prune Griffin poplar except, as for the other poplars,
for corrective purposes.

Ash, elm

Both ash and elm are widely planted as boulevard trees. Wider-
crotched scaffold branches on the elm will result in a slightly
stronger tree. Both of these species are slow growing, large trees.
Early training and thinning are the most important pruning
requirements.

Crabapple, mountain ash, Prunus species

These species are grown for their abundant floral display; some are
also grown for their colourful foliage. Pruning should entail
thinning to keep the crown open: before bloom in the case of the
crabapple, after boom in the Prunus species. Directing strong
scaffold branches is also important in ornamental trees. Crabapples
and Shubert chokecherry are grafted onto suckering rootstock, so
you will need to remove sucker growth annually.

Birch

Birch require very little pruning. Do not allow weeping birch to
form a low fork (1 to 2 m from the ground), as this will become a
split crotch. The tree will naturally divide again at about 3 to
4 metres, which should be allowed. Remember to prune only in late
June or early July to avoid excessive bleeding.

Bur oak

This is the only true oak that is hardy in Alberta. It is slow growing
with a strong taproot therefore, it is not easily moved. Prune out
double leaders.

Maple

Crown thinning is required annually on maples but wait until late
June or early July to avoid excessive bleeding.

Larch

This is the only deciduous-coniferous tree growing naturally in
Alberta. Prune out double leaders.

Pruning evergreen trees

The main evergreen trees in Alberta are spruce and pine.
Evergreens grown as specimen trees should not require anything
except corrective pruning, i.e., cutting out dead, damaged, or
diseased branches. If the leader of an evergreen tree is either cut or
accidentally broken, immediately tie up one of the top lateral
branches to form a new leader. If this is not done, there will be two
or more terminal growths competing for dominance. The resulting
double or triple leader will have a very weak crotch that is
susceptible to wind damage.

Figure 11. Leader damage

as a new leader are removed

Limit pruning pine and spruce to partially removing the new
growth (candles) at the terminal of each branch or twig. Pinching
back up to one half of this growth on pines and cutting spruce back
with hedge shears will tend to contain the growth in the current
year. If you pinch back every year, you will have a denser, bushier
looking tree. Do this after the candles have elongated, but before
the new needles have opened out. Usually late May is the best time
to pinch back the new growth.

If you cut back into old wood that has no needles on it, then that
branch will probably die. As Figure 12 shows, you can cut back
spruce back further than you can pine.

Pine and spruce have a natural needle cast, so they are not the best
types of tree to use as a hedge material. If you maintain them at a
constant height and width, they will tend to become very thin. This
makes for a very unsightly hedge.

Figure 12. New growth on spruce and pine

PICEA (spruce) |

last year's 2 years' 4 year's growth 6 year’s growth
growth growth

1st year 2nd year 3rd year

Needles of spruce hold for six to seven years; pine needles average three
years before dropping. Spruce withstands more extensive pruning.

Pruning shrubs

Shrubs are grown for the beauty of their foliage, stem colour or
bloom, or for their screening effect as a hedge. Sometimes these
purposes are combined, as in a hedge of lilac or red osier dogwood.
There are many different kinds of shrubs and many different ways
to prune them, but some general rules of thumb can be applied
(with exceptions) to shrubs. Shrubs that bloom before June 20
should be pruned immediately after the bloom period. Shrubs that
bloom after June 20 and are grown for foliage or stem colour
should be pruned in the dormant season or just before growth
appears in the spring.

There is a commonly held, but quite incorrect idea, that all shrubs
should be pruned, and pruned hard, each spring. This may take the
form of shearing the shrub into a neat ball or severely cutting back
branches to keep the shrub within bounds. Both techniques result
in a misshapen, ugly specimen with few or no flowers.

Figure 13.

it

n

Shrub pruned to remove about one-
third of the old wood and most of the
crossing branches. Most flowering
buds on new wood remain.

Unpruned shrub

Figure 13. continued

Sheared shrub still has
too many old and
crossing branches,
while many important
flowering buds have
been cut off. Not
recommended.

If you are in doubt as to when to prune, it is probably preferable to
leave the shrub alone. Most shrubs have a naturally graceful
growth habit and only require pruning every other year. Some
shrubs only require a low maintenance pruning schedule; one that
removes three to four of the old stems and allows three to four new
ones to grow each year Shrubs should have corrective pruning
done each year.

An understanding of the basic principles behind pruning and
knowledge of the growth habit and the method of flowering of the
plant concerned are important, particularly the age of the wood on
which the flowers are borne.

Shrub recommendations

Early flowering shrubs (bloom prior to June 20)

These shrubs bloom from buds set on last year’s growth and your
aim should be to promote more flower buds for the next year. To
accomplish this you must encourage strong new growth that will
set buds during the current growing season. Prune immediately
after bloom has finished. Prune by thinning out weak stems and by
heading back selected stems to promote strong lateral shoot
development. Unpruned shrubs of this type usually become twiggy

and ungainly with few flowers each season. Early flowering
examples are: some mock orange varieties (Philadelphus), lilacs
(Syringa), some spirea varieties (Spirea), and flowering plums
(Prunus).

Late flowering shrubs (bloom after June 20)

These shrubs bloom mainly on wood grown during the current
year, but some do bloom from buds set the previous year. If the
bloom period starts near the end of June (in the case of some
potentillas) the first early flowers could be from buds set on one-
year-old wood. The remainder of the summer bloom would be on
current growth. By pruning, you want to create a large number of
strong, current year twigs and thereby a large number of flower
buds. Potentillas retain their shape naturally, so they only require
minimal pruning and perhaps some annual thinning. Spireas, on the
other hand, usually require severe cutting back of all stems to only
two to four buds from the base to encourage new growth for late
summer bloom. Lilacs and honeysuckles require regular pruning, in
the case of lilacs to keep them from becoming thick and
overgrown.

Foliage and stem colour shrubs

The desired effect you want to achieve is that of either a large mass
of coloured (or variegated) foliage, or the production of many new
woody stems for best winter colour. Both entail pruning hard each
spring to force a great deal of new twiggy growth. To be successful,
you must also feed and water these shrubs well to keep them
healthy and vigorous. Some people prefer to cut almost to the
ground each year; others will allow a basal framework to develop
and cut back to that frame each spring. Both methods will
accomplish the same objective.

Evergreen shrubs

Most evergreens require minimal, if any, pruning. They should, if
space allows, be allowed to develop naturally. The occasional
removal of a wayward shoot that detracts from the overall
symmetry is usually all that is required. Juniper responds well to
having vigorous shoots trimmed back to a side branch. Cedars

respond well to shearing to help keep wayward shoots in check and
maintain the overall shape of the plant. Mugo pine can be kept
dense by pinching new candles in half each spring.

Hedges

Hedges require early pruning to encourage dense basal growth and
further pruning to keep the basal growth well leafed out. The top of
a hedge should be narrower than the base so that it will not cast
shade on the lower branches. If the hedge base is shaded, it
becomes leggy and open and will not serve the purpose of the
hedge.

Figure 14. Hedge cutting

Pruning roses

Although they could take a full book themselves, this will be a
short note on roses. Most people have a rose or two in the home
garden; whether these are newly purchased tea roses or are hardy
shrub roses will make no difference to these instructions.

In the wild, roses produce strong new shoots from near the base of
the plant each season. In the following years the secondary, or
lateral growth from these shoots becomes progressively weaker.

Food taken in by the roots is directed to new growth and eventually
the original shoots are starved out - a natural but slow method of
pruning. Pruning roses short-circuits nature by cutting away the old
shoots and encouraging vigorous disease-free new growth and a
large number of flowers.

Rules of thumb for pruning roses

1 . Cut with sharp tools above a new bud at the correct angle.

2. Cut back into healthy wood. If the pith is brown or discoloured,
cut the shoot back until healthy white pith is reached or to a
strong vigorous bud.

3. Cut to an outward pointing bud to encourage an open centre
habit.

4. Only allow one shoot to grow from a pruning cut.

5. Completely cut out any diseased, dead or damaged growth along
with any weak, spindly growth.

6. Keep all branches well spaced to allow free airflow through the
plant and to allow light to reach all leaves. This lessens the
likelihood of such diseases as black spot and rose mildew, which
thrive under stagnant air conditions.

7. Remove pruned branches from the area to reduce the possibility
of spreading disease. Place them in the garbage or, if allowed,
bum them.

More detailed rose pmning methods should be obtained by reading
other manuals that cover all aspects of rose growing.

Figure 15. Roses produce flower buds only on wood produced in the
current season. Old wood can be severly pruned as shown

#

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f

Pruning fruit trees

There are three principal methods of training fruit trees:

Central leader system: The central leader is allowed to grow
unchecked. This results in a tree that is usually so large you need a
ladder to pick the fruit. Such trees make fruit harvesting less
convenient and riskier.

Modified leader system: The young tree is allowed to grow
naturally but the main scaffold branches are selected at well-spaced
intervals. Once five to seven scaffolds are selected, the leader is cut
out (modified) and the resulting tree is shorter in overall height and
usually wider in spread. This is the preferred method for training
fruit trees in Alberta.

Open centre system: This is a more severe modification of the
central leader (usually cut between 0.75 to 1 m from the base)
resulting in a low-headed tree that has a number of scaffold
branches close to the base of the tree; this is inherently a weaker
structure. This method is not recommended for prairie conditions.

Each species of fruit tree is pruned in a slightly different manner
because of the placement of fruit buds (either spurs, shoots or both)
and general differences in growth habit.

Figure 16. Central leader system Figure 17. Modified leader system

Figure 18. Open centre system

Apple

Fruit is borne at the ends of spurs that form on branches two years
old or older. Some fruit is also borne on new one-year-old wood.
As pruning is done to encourage fruit spur development, thinning
out entire branches (rather than heading back) is the most desirable
practice. Spurs may live for eight to 10 years.

Plum

Fruit is borne on lateral spurs, which may be 1 cm (Japanese types)
to 1 m long (European types). The bearing life of the spurs is from
six to eight years. Pruning should be limited to creating a strong
main frame on the tree with little or no heading back.

Apricot

Fruit is borne on one-year-old shoots and on short spurs which
carry most of the crop. The spurs only live two to three years,
therefore, pruning should be heavy enough to continue new growth
and to develop new spurs to keep the tree bearing. The modified
leader system is recommended.

Pear

Fruit is set on spurs that have a long life. Pruning is almost
identical to that for apple trees. More scaffolds can be left on a
modified leader frame.

Pruning bush fruit

Raspberries

There are four types of raspberries grown in Alberta: red and
yellow, black and purple. Pruning procedures for red and yellow
raspberries differ from those for black and purple raspberries.

Red and yellow raspberries grow canes in their first season with no
fruit. In the second season, the canes grow lateral shoots that bear
fruit. At the end of the second season, the fruit bearing canes die.
Pruning entails cutting these dead canes in late summer or early
spring and thinning weak new canes to promote only strong canes
in each clump.

Black and purple raspberries grow new canes with laterals in their
first season. In the second season, more laterals are produced and
all laterals will flower and bear fruit. The canes die after bearing
fruit. Pruning should entail cutting one year old canes down to
about 0.5 to 0.75 metres, which will encourage more lateral

development in the second season, which in turn will result in a
heavier crop. The pruning out of two-year-old, spent canes and
thinning out the weak new canes should be practised each season.

Currants

Red, white and black currants are grown in Alberta. Red and white
currants bear fruit on spurs of two and three-year-old canes. Older
canes bear inferior fruit, so pruning is aimed at keeping old wood
thinned out and new wood growing in. The well pruned red or
white currant bush will have three stems each of three, two and
one-year-old wood. Black currants, on the other hand, bear their
fruit on last season’s growth. It is, therefore, necessary to keep new
growth coming in and old growth almost totally cut back. Ideally
black currants should have nine canes with three to four, two-year-
old canes and five to six canes from the previous year’s growth.

Gooseberries

Gooseberries belong to the same genus as currants (Ribes) but are
pruned to have nine canes with three each of one, two and three-
year-old canes. Fruit is borne along the sides of one-year-old shoots
and on spurs on two and three-year-old wood.

Figure 19. Pruning currant and gooseberry

One year branch

Two year branch

Figure 19. continued

Bush cherries (Nanking, Korean and Mongolian)

Bush cherries are treated the same as gooseberries with nine stems;
three each of one, two and three-year-old wood. Pruning should be
aimed at keeping the bushes open to allow fruit to set within the
centre of the bush.

Saskatoons

Fruit is borne on one-year-old and older wood with the youngest
branches bearing the largest, sweetest fruit. Prune to control height
(2 to 2.5 m); thin the centre to keep it open and cut off low
branches.

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