Pruning and trimming
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Many gardeners never prune their plants
because they are scared of damaging them. The reason for this unfounded fear is
that pruning has been made to appear more complicated than it really is.
There’s no great mystery to pruning, particularly pruning ornamentals, and
there’s really very little that can go wrong.
There is a difference between pruning and
trimming. Pruning is a training method; the cutting makes the plant grow in a
desired direction or shape or encourages the growth of a particular type of
wood. Trimming is simply removing excess growth and reshaping an already
existing structure.
The theory of pruning
The main reasons for pruning are to
promote strong new growth that rejuvenates the bush, to produce a well-shaped
plant, to maintain plant health and to produce good crops of fruit or flowers.
Pruning is also important in maintaining good ventilation, which reduces fungus
problems, and allowing light to penetrate to the centre of the bush or tree.
When shaping a plant you must have an
understanding of the way it develops. Severe trimming and topping are damaging
in most cases. Not only do they spoil the shape of many plants they can also
weaken the plant, especially if the repeated at regular intervals. Regular
pruning lessens a plant’s photosynthesis ability and depletes its stored
reserves.
Heavy pruning can also produce branches
that grow at acute angles. These are more easily damaged by wind or may
eventually break under their own weight. Careful trimming and thinning, however,
can strengthen a plant by removing weak branches and enabling the plant to
channel its energies into stronger growth.
Most woody plants grow primarily from the
branch tips. That’s where the new spring growth will start then it will
progress back down the branches. Growth hormones are more concentrated in the
growing tip and this tends to inhibit lateral branching. This is known as apical dominance and is seen at its
most extreme in the strong suckers or water-shoots that occasionally break,
usually from the base, and race ahead of the main growth.
Apical dominance remains even if the
branch tip is removed. With most trees and shrubs, you can expect that it will
be the bud immediately below any cut that will be the first to start into
growth. That initial growth spurt will often suppress the growth of buds lower
down. This is important because it enables you to determine the direction of a
branch’s growth.
Consider the ultimate shape of the plant
before you cut. Bearing in mind that any branch will tend to shoot from the bud
immediately below a cut it’s clear that if the centre is to remain open you
must cut to buds that face away from the centre of the plant These are known as
outward facing buds. In some instances you may wish to leave a few inward facing
buds to fill in the centre of an otherwise loose growing shrub.
Many times a plant is just too dense and
twiggy to prune it with precision. In these cases and all over trimming and
thinning will usually suffice. There’s no point in attempting to cut to outward
facing buds on something like a Hebe or a low bushy conifer.
The practice of pruning
When is the right time to prune? The
answer to that depends on the type of plant and the severity of your winter
climate. Hardy deciduous plants are usually best pruned in the winter. They are
unlikely to be damaged by the cold and will be less likely to bleed (ooze sap)
during winter. Frost tender plants are best left till spring; cutting back over
winter only exposes the vulnerable cut stems open to frost damage. Spring
pruning will still allow for an entire season’s growth before the next winter.
It is generally recommended that the best
time to prune most hardy plants is late winter. This is mainly because the
branch structure is more easily seen when the plants have few leaves but
there’s no reason why you shouldn’t trim and thin in summer if you wish. Don’t
cut back too early as spring pruning can lead to cuts that refuse to properly
heal. Shaping the plants during the growing season, when you can readily see the
effects, is often easier than trying to envisage exactly how the growth will
develop after winter pruning. Hedges may need two trims during the growing
season.
How far to cut back? That’s the question
that always that leads to confusion. You can find all sorts of theories about
how hard to cut back and why but it all comes down to the initial reasons for
pruning; renewing vigour, maintaining health and shaping. As mentioned earlier
too severe a trimming may actually lead to reduced vigour and a poorly shaped
plant.
Ensure that your secateurs (and saws too
if heavier weapons are needed) are sharp so that all the cuts are clean. Trim
so that water runs away from the bud. When trimming side branches remember to
first make an undercut on the lower side to avoid the bark tearing as the
branch falls.
The exact method of cutting of side
branches is open to debate. The old school of though was that you cut as flush
as possible to the main stem then sealed the wound with a pruning paste or
paint. Recent research suggests that it may be better to leave a stub, or
crown, and only use pruning paste (preferably one with anti-bacterial agents)
on plants that are prone to infection, such as apples and pears. This appears
to encourage a more rapid formation of callus tissue and therefore quicker
healing.
The general methods for pruning shrubs
and small trees are as follows. First look for strong branches of the previous
year’s wood. Having identified these main stems completely remove any old,
diseased or spindly branches so that just the main stems remain.
The primary objective is to maintain
health. You have already removed the old, diseased and spindly wood, now take
out any overlapping branches, water-shoots and basal suckers. What is left will
be a healthy but unshaped plant.
Cut back each main branch to the first
outward facing bud you find the stand back and look at the shape of the bush.
It will grow well but is it going to be the shape you want? If not trim back to
lower outward facing buds or those that will grow to the shape you require,
making sure they are on good wood, and remove any misplaced branches. Does it
have too many main branches? If so thin out some of the branches, you really
only need four or five main stems. Is it still too tall? If so cut lower down.
To summarise, the procedure for winter
pruning is as follows.
- Completely remove any diseased, damaged or weak wood.
- Remove suckers and overly vigorous water-shoots.
- Locate the healthy main branches formed during last season’s growth.
- Cut back to healthy outward facing buds.
- Assess the results and adjust as necessary.
Always remove any fallen debris and spray
with a fungicide after pruning. You may well have disturbed fungal spores that
will find an easy entry to the plant by way of the freshly cut stems.
A pruning paint or paste can be used to
seal the cuts but as mentioned above there are doubts about its long term
merits. It may prevent immediate fungal infection but it could also slow down
or prevent proper healing.
Pruning berry fruits, vines, canes and fruit trees
The correct pruning of fruiting plants is
a very important part of ensuring that you get the best crop possible. You’ll
always hear stories along the lines of: “I’ve got an old plum tree, never
prune, and it always has a huge crop of plum. Good ones too”. It may be so but
it wouldn’t pay to bank on your trees performing the same way.
Fruit pruning, particularly fruit tree
pruning, is a little more complicated than pruning ornamentals. It’s a
combination of thinning, shaping, maximising the plant’s potential and
improving its crop. Improving the crop means getting the best fruit not
necessarily producing the largest possible quantity.
The most important of pruning fruit crops
is understanding where, and how, the fruit forms. Some plants, such as plums
and cherries, flower and fruit on the previous season’s growth. Others, such as
black currants and grapes flower and fruit on the new spring growth. Both types
may produce fruiting “spurs”, that is a special type of growth, distinct from
the normal wood, on which flower buds form.
Berry fruits
The pruning method depends on the type of
wood on which the fruit forms. Raspberries, boysenberries and loganberries
fruit on the wood of the previous season. Remove any canes that have already
fruited immediately after the crop is harvested. Cut back the fresh canes in
August to encourage branching.
Black currants fruit on the first year’s
wood so they may be cut back hard each winter. Gooseberries, blueberries, red
currants and white currants flower and fruit on new side shoots so some old
wood must be retained. Thin out tow and three year old branches to encourage
fresh new growth.
Fruiting vines
Most fruiting vines flower on the new
growth so they can be cut back hard each winter. With grapes cut the lateral
growths nearly back to the main trunk in winter. Leaving too many fruiting
spurs will result in overcrowded undersized fruit that may fail to ripen
properly. Be prepared to sacrifice some quantity to raise the quality. Thin any
very large bunches of grapes: nearly always there will be a few grapes that are
obviously going to be of poor quality, they are the ones to remove.
Stone fruit
Peaches and nectarines flower on young
wood so remove any branches more than two years old. Plums, apricots and
cherries flower and fruit on older wood too, which allows greater leeway when
pruning. After the initial framework of the tree is established little pruning
should be needed. Any pruning should be done as soon as possible after harvest
to lessen the risk of silver leaf disease.
Citrus
Most pruning can be done when harvesting
the crop. Cut the fruit from the tree rather than picking it. Cut the stem back
to a firm outward facing bud and thin out any weak growth. Other than this
little or no pruning is required or desirable. If you do have to cut back
overgrown old trees do it in spring after any risk of frost damage has past.
Other fruit
In most cases deciding when and how to
prune is a matter of determining whether the fruit forms on the old or new
growth and pruning accordingly.
Apples and pears
Apples and pears have distinct fruiting
spurs that are instantly recognisable once you know what they look like. All
wood above the spurs can be removed as can any weak or unproductive shoots.
After the initial training the framework of the tree is easily maintained by
cutting back to the fruiting spurs.
Avocado
Avocados should be kept cut back so they
remain compact. They flower and fruit over quite a long season so any pruning
is bound to affect the crop to some extent. Nevertheless, some cutting back is
usually desirable. Do not prune if there is a risk of frost damage.
Fig
When trained against a wall aim to keep
about five to eight strong shoots. The oldest of these should be removed each
year to make way for new wood. Figs often produce crops in spring and autumn.
Any pruning must be delayed until the spring crop is ripe, which may mean some
of the autumn fruit has to be sacrificed.
Tamarillo
Any frost damaged wood should be removed
in spring along with any weak or unproductive growth. Tamarillos are relatively
short-lived and need to replaced at regular intervals. Old trees are seldom
worth the trouble of corrective pruning.
Copyright Geoff Bryant
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