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Introduction
Excerpt overview
Technique widely applicable and
practical
Set limits for your plants
Be aware of the plant's growth
rate
3 good times for restriction
pruning
Start clipping at the top
Choosing main limbs
Step back to assess the
shape
Direct the new growth
When to have confidence in leafless wood
What about flower
Be considerate of the plant's
effort/expense
Diagram, deciduous
tree
Diagram, pyramidal
evergreen
Hands-on training
Above: This space is too small
for a full sized blue spruce,
50 feet tall and 25 wide. Yet at its present size its blue
form
is attractive there. So we prune this spruce to keep it this
size;
it was pruned the year before this photo was taken. Starting
at the tip, Janet removed over three feet of the leader,
selected and tied in a new leader. Then she descended each
side and shortened branches there by 1 to 3 feet to keep
the narrow pyramidal form. The tree can grow for two
years before being pruned again.
Most
gardeners overplant. One property may
be too thick with trees, planted by a gardener who had no idea that
those s/he planted would grow so quickly. Another may be a shrub
jungle belonging to someone who didn't double-check the garden
center tag descriptions, unaware that shrub size on such tags is
often grossly understated. These gardeners may be overwhelmed and
even embarrassed by plantings grown far out of control.
A third property may be planted with even more trees and shrubs
than either of the first two, yet its gardener is in
control and pleased with the attractive result. The
difference is this third overplanting was done with an awareness of
each plant's potential size and growth rate, and the intention of
pruning each one to restrict its size.
You can be that third gardener, able to have a diverse
collection of trees and shrubs yet keep them in line indefinitely.
All the basics are here in this article, and August, November or
February are good times to apply them in your garden.
A
technique widely applicable and practical
Any tree or shrub can be kept smaller than its potential, if
you're willing to do the necessary pruning at appropriate
intervals. Doing this is not difficult and does not take much time
-- 30 to 60 minutes per plant is about average. It can be done just
once a year or once every two years, depending on the
plant's growth rate and how
crisp or loose you want the plant's outline to be in the interim.
The more crisp the desired look, the more often a plant must be
pruned.
So why don't more people keep their plants in line? Because too
few realize it's possible or necessary. Very few have done what we
have in seeking and studying trees and shrubs kept attractively
small and healthy for decades or centuries. (
Such places as this...) Only a handful buck standard American
pruning convention by committing the technique to paper or
conducting classes.
So what you read here or learn in our
hands on sessions may contradict what's in other pruning
guides. We aren't here to defend the differences. (
Check here!) Plants we have pruned this way for decades and
others that have been pruned this way for generations make a better
argument. There are no absolutes in pruning. How and when we prune
depends on our objectives, which vary as much as our personalities.
This technique is just one more way to prune, as applicable, safe
and practical as any other in the right situation.
First, set limits for
your plants
The first step in restriction pruning is to draw some lines.
Decide how tall and how wide you can allow the plant to become.
Often, the tallest we allow is "gardener plus a ladder" because we
do not want to work from special lifts, erect scaffolds or bring in
heavy equipment.
Recently we planted something that some authorities report as
growing just 10 feet tall and wide. Yet it is from a species with
the potential to be 20 to 30 feet tall and wide. It's a variegated
angelica tree. (Aralia elata 'Variegata' -- thanks to Goldner
Walsh Nursery manager Joel Miller, who tracked down this
beautiful, hardy, rare tree so customers like us can finally have
one of our own. We hope you also ask at your local garden centers
about special plants, because many garden centers are willing to seek
special plants for you.) The place where we have planted it can
only accommodate a tree that's ten by ten, so we will watch it and
be ready to cut if it oversteps those bounds.
If that happens, we will begin pruning it in the year it becomes
too tall, too wide, or both. And we'll plan to prune it every year
or two from then on.
Above: The first step in keeping trees and shrubs in bounds
is to set firm limits. We are willing to let our own red
horsechestnut (Aesculus x briotti 'Carnea') grow to its
full potential, 30 to 40 feet tall and round. In smaller quarters
in a client's collection, we might set its maximum height at "Janet
plus a ladder" so we could prune as needed without special
equipment.
Right: You decide how tall and wide you can allow a tree or
shrub to become. These limits also describe a shape. For simplest
pruning, the imposed shape should conform to the plant's natural
habit, as it does here for this naturally round red
horsechestnut.
Be aware of the
plant's growth rate
Whether we prune a plant annually or every two years depends on
its growth rate. A tree like redbud (Cercis canadensis)
can produce shoots three or four feet long in one year, which means
it may jump that far past its bounds each growing season. We're
likely to put that plant on an annual pruning list. On the
every-other-year list are slower plants like dwarf false cypress
(Chamaecyparis obtusa 'Aurea') that grows just 6 inches
per year. (But slow doesn't mean small, as you can see where Steven
cut two "slow" dwarf falsecypresses!)
To gauge the
growth rate, look at how much new growth there is on the end of
a branch at or near the top of the plant. There is a change in bark
color, and often a branch-encircling ridge called the terminal bud
scar, between old and new growth.
Don't judge a plant by the growth rate of its side branches,
branches near the bottom or in the interior. Look at the tip buds
and tallest limbs to decide how much the plant grows in one
year.
The bud at the tip of each branch will grow more than those
behind it along its limb. Also, the bud at the very highest point
of the plant will grow more than all others. Sometimes that tip bud
of the highest limb or "leader" produces a shoot twice as long as
those below it on the same branch, and three times longer than
those on the lowest limbs.
Above: This red horsechestnut branch grew from one fingertip
to the other this year. Its dominant bud grew a bit more than
twelve inches, while its twin grew only half that. The new growth
has lighter bark color, and begins at a twig-encircling ridge --
the terminal bud scar. (What may look like a dead, bud-less
tip above the new tip buds is a spent flower stalk. It will be shed
in time.) The buds now set at the tip of the branch will
repeat the process next spring, one of them exhibiting its
dominance by outgrowing its twin.
Right We prune this redbud every two years to keep it the
size you see here. Next year we'll cut each main limb
back by five or six feet. The tree will quickly cover its truncated
form in new foliage.
When we prune the redbud, we cut each main branch at about
the spot where it's been cut before. One such old cut is here in
the "Y" above the saw tip.
Three good times for restriction
pruning
It's important to recognize that hardy plants grow in this
orderly fashion, following an annual schedule including a time when
they stop extending new growth as they set themselves up for
winter. We like to do our restriction pruning during periods after
a plant has set its next year's buds but before the next spring's
growth begins. In Michigan that's between mid-August and early- or
mid-April; we most often do this pruning in August, in November
after leaf-fall or in February during a thaw.
When we cut after mid-August, the plant doesn't have time to
make much or any new growth. The form we see when we finish pruning
will not change until new growth begins. That can be as much as six
months, a long time for something to remain "done" in a garden.
So it's a good thing to prune a plant in August if that plant
will be attractive immediately after being pruned. A yew or spruce
that looks shaggy at the end of its period of unrestricted growth
takes on a more neat outline right after pruning. We can enjoy that
neat shape all winter.
On the other hand, we're more likely to prune in late winter or
very early spring if the tree or shrub has to be pruned quite
hard to keep it within bounds. An example would be that redbud
which must have its limbs shortened by 3 or more feet. It can look
a bit stark until new growth begins.
By the time it quits growing to harden itself for winter, the
tree or shrub has already set its growth hierarchy for the coming
spring -- its tip buds have been programmed to grow faster than
side buds, highest bud faster than all. If we remove tip buds after
this growth hierarchy has been set for the coming spring, there is
no time left for new growth to form, mature and change the pecking
order. We clip off the tip bud on a branch, leaving in place a
batch of side buds programmed to grow at relatively equal pace for
much of the season, a rate that is more sedate than what the tip
bud would have achieved.
So doing this pruning between August and April has the effect of
slowing the plant's outward and upward reach during the next year.
Its energy is divided among more limbs, all of which will remain
for a longer time within our set outline.
Start clipping at
the top
Even so, the plant will tend to grow longer shoots from its top
than from the sides and bottom. So the top takes the biggest cuts.
Thus we always start at the top of the plant when we prune to
restrict size. 
Right: If the plant has more than one main limb, we start
with the tallest. That would be limb 2 or 3 in this
sketch.
We'll cut that main limb back far enough that its leader can
grow without crossing our line until we plan to prune again. We cut
it back by two years' growth if we're on a two year schedule. If
the plant is to be cut annually, we cut each of those limbs back
just one year's growth inside our line.
After cutting back the top of a limb, we shorten its side
branches as necessary. We can be less harsh with these, since as
side branches they will not grow so much as the tip would have. We
simply shorten or remove side branches as necessary to keep growth
within our limit and eliminate clutter.
Then, if it's a tree with multiple main limbs as in this
sketch, we move on to cut the other main limbs the same way:
Shorten the top and then trim side branches.
To make shortening cuts to the end of each branch, see the
Diagrams, pyramidal evergreen
and deciduous tree
Main
limbs are your choice
Selecting the framework for pruning is where some art comes into
play. It's up to you to decide that the tree represented by the
sketch above will be most beautiful with just five main limbs.
Choose for limbs that separately and together draw graceful lines,
and for branches that don't fight each other but can each occupy
their own parts of the sky.
Above: "Fight for the sky" is a concept requires
considering the tree as it appears from above. Here's that
same cartoon tree with its "keeper" limbs and their foliage
outlined from above. Although there is some overlap, there are no
big duplications. Whenever you prune, you remove limbs that "cross"
from one main limb into other limbs' territory, such as any branch
that sprouts from main limb 3, crosses the center of the canopy and
mixes with main limb 5's twigs.
Once those five are designated as "keepers," that guides
decisions about which side branches are cut and how much, after the
main limb's shortened. In this example, limb A will come off
because it's duplicating limb 1's foliage -- trying to fill the
same air space. Likewise, limb B is cramping limb 3's style, and
limb C must go because it makes the tree look bushy and its leaves
are vying for the same air space as those of limbs 3 and
4.
You can see photos of main limb selection and examples of
overall effect such as these below, in Cut to control blue
willow and Crabapple shaped and
reduced:
Step back
to assess the shape
Natural shape's easiest!
As we cut side- and lower branches, decisions have to be made
about shape as well as size. Step back from the plant from time to
time as you prune. Take in the pruned top as well as the side
you're currently working. From a distance you will see the whole
picture and make better choices.
This begs the question of what shape a plant should be. That's
totally up to you, but it can be a good idea to take the plant's
natural form as a guide.
Some plants grow about as tall as wide, forming a round crown.
Others are naturally pyramidal, columnar, horizontally spreading or
vase shaped. If you prune to enhance the natural shape rather than
to create a form that's contrary to that plant's nature, your
annual or bi-annual pruning will be simpler and there will be less
touch-up pruning to do on "errant" shoots in between.
Direct
the new growth
As you trim each limb (see diagrams pyramidal evergreen and deciduous tree; and see Afraid to cut Japanese
maple for photos of reducing and thinning limbs) imagine
the remaining tip buds' growth. Whichever are highest above ground
and furthest along the branch will eventually become dominant. The
energy of the whole branch will flow first to the tip and top buds
and the limb's growth will go in the direction they "point."
Sometimes it's necessary to shorten limbs that passed first
muster, in order to leave one chosen bud in the lead. What you're
doing is shortening branches that threaten the dominance of your
chosen lead bud. In the case of the very highest bud remaining on a
plant, the one you expect to take over as primary leader, you may
want to take the extra step of using a soft, biodegradable tie to
hold it in an upright, superior position until spring. Nature will
take it from there.
Some plants sprout from bare wood,
some don't!
On most needled evergreens including juniper, arborvitae, pine
and spruce, new growth will begin only from a branch that has
both needles and a tip bud. If you cut a limb on one of these
evergreens to leave only a needle-less or tip-less stub, it will
remain or become bare, then die. So make important cuts to just
above side branches that have needles and tip buds. Take out any
needless wood. (Photo examples of cuts to just above needled side
branches in Shag cut for low
juniper in Shrink or shape
birdsnest spruce, and in Prune a mugo.)
Try not to worry about leaving gaps. Step back and look from a
few paces away. Rest assured the remaining buds will grow to fill
what may seem terrible gaps from close up. (Photo example in Shape
a dwarf white pine.)
All deciduous plants -- those that drop all their leaves each
year -- as well as evergreen rhododendron, azalea, euonymus,
boxwood and yew, can sprout from leafless wood. So cut away!
What
about flower?
We worry too much about flower. Pruning in late summer can
certainly remove flower buds, but if you prune as described here
flower buds will also remain on the plant. You only lose the bloom
on the part of the plant you don't want -- the part that would be
too tall or wide. (More about all kinds of pruning, and adjustments
sometimes made for flowering species, in
What's Coming Up 86.)
If you can't stand to lose a single bloom, then change your
pruning schedule to do everything I've described here but do it
within a few weeks after the plant blooms. That means you'll prune
a cherry in late May, redbud and crabapple in June, and mophead
hydrangea and weigela sometime in July.
In these cases you will find that you
have to do touch-up pruning in addition to an annual or bi-annual
clipping. Now and then during the year you'll have to thin overly
bushy limbs and remove tips that break away from the outline.
That's because pruning post-bloom, during a season of active
growth, will stimulate branching and allow the plant time to set up
a new tip dominance after the cut.
We prune this redbud every year right after it flowers. It
blooms well but also needs touch up pruning throughout the year to
keep it from overstepping its space in this small garden.
Be considerate
of the plant's efforts and expense
When you finish your restriction pruning the plant may have lost
a third or half of its buds or leaves, and a good portion of wood.
The plant expended energy and used resources from the soil to make
that material. It's time to pay for this.
In restriction pruning we do want to reduce a big plant's energy
to some extent. That helps in the effort to keep it small. Yet we
can't overlook the fact that plant parts which formed and were
removed from the site before their time represent a drain on the
soil's nutrient bank.
So spread an organic, slow
release fertilizer over the root zone of the plant. Scratch it
in or cover it with mulch.
Now you're done for a year or two. Enjoy the shapes you've made
and the realization that you can plant even more so long as you
keep pruning.
Here's another good reason to do restriction pruning of
evergreens in fall. The top of this hemlock will make a beautiful
small Christmas tree, and the clippings from side branches can make
a wreath for the door.
Restriction pruning, step by
step
Deciduous tree or shrub:
1 - Set height and width limits as you desire.
2 - Check top growth to determine the plant's growth rate.
3 - Reduce the top growth to within your desired outline. Reduce
it by one or two years' growth, to match your pruning schedule.
This tree will be pruned annually, so its leader will be cut as
shown. Remaining tips will be able to grow for one year before
breaking the height limit.
4 - Some branches may remain that are within one year's growth
of a height or width boundary. This is acceptable. Since they
formed as interior and side branches, their growth will be slower
than a tip branch for much of the next year.
5 - Tie in a new leader, if desired for shaping. Use soft, wide,
biodegradable material to tie a flexible side branch into upright
position. Prune all other branches to preserve the status of the
tip of this new leader. It must be the highest bud on the
plant.
6 - Shorten all other main branches so they can complete one
year's growth but still be within the desired outline. Clip each
one back to a side branch that will become a well-placed, graceful
new tip. It may be necessary to prune branches that may compete
with this new tip.
Note - This drawing is two dimensional, a "slice" through a tree
which has main limbs radiating in all directions from the trunk. In
most cases you will be pruning numerous sets of side branches,
which are not shown here in order to more clearly illustrate the
process.
Step
by step: Pyramidal evergreen
1 - Height and width limits you set. Pruning is simpler if it
enhances the plant's natural shape, rather than imposing an
unnatural shape. This spruce is easy to maintain as a pyramid. It
would require more frequent touch-up if pruned into a column or
rounded form.
2 - Check top growth to determine the
plant's growth rate.
3 - Reduce the top growth to within
your desired outline. This tree will be pruned every two years, so
its leader will be cut as shown. The new tip will be able to grow
for two years before breaking the height limit. The cut leaves a
stub which will serve as a brace when the new leader is tied
in.
4 - Tie in a new leader if necessary.
(Unnecessary in this example, where only a very young shoot remains
to become the new leader.) Use soft, wide, biodegradable material
to tie a flexible side branch into more upright position. Prune all
other branches to preserve the status of the tip of this new
leader. It must be the highest bud on the plant.
This spruce tip came from a spruce
I prune every two years to keep it 10 to 12 feet tall and 6 feet
wide. Its growth rate is about 18 to 24 inches per year so I
remove at least 3 feet of leader each time I prune it, and tie in a
side branch as a new leader.
5 - Shorten all other main branches to
two year's growth within the desired outline.
6 - Some branches may remain that are
within two years' growth of a height or width boundary. This is
acceptable. Since they formed as interior and side branches, their
growth will be slower than a tip branch for a year or two.
Note - This drawing is two dimensional
and shows only the uppermost part of the plant in order to more
clearly illustrate the process. In most cases you will be pruning
numerous sets of side branches, radiating in all directions from
the trunk. In Reduce a Spruce you can see
this process in photos.
For
hands-on practice in this technique:
Attend
Garden by Janet & Steven pruning sessions and
classes (we post them as they are scheduled, in Where
we're appearing.) There you can complete that step that is
so important to many gardeners, to try the process hands-on.
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