The Fine Art of
Pruning
In order to have full, compact and healthy begonias,
most need regular
pruning. Regular usually means once a
year. Pruning is also necessary to shape
a begonia for a specific purpose such as to create a standard or a
hanging basket. In this chapter we'll
discuss all the
different types of pruning and pruning specifics for the different
types of
begonias.
As a general rule, begonias grown outdoors in warm areas
are pruned in
the spring and those grown in cold areas are pruned in the fall. There are reasons for this.
In warm climates such as Southern California,
Florida, parts of Texas and other frost free areas begonias are grown
outdoors
all year round. In these areas begonias
are usually pruned in the spring, March through June.
The reasons for this are: Begonias
pruned in the fall can winter-kill
because of the wet winter conditions. Usually growers use the pruned
parts for
cuttings to start new plants and these don't start as well in the fall
and are
hard to carry over to the next Spring.
Most canes start blooming later in the summer so if you prune in
the
fall you shorten the blooming season you would ordinarily have. In cold climates begonias are pruned in the
fall for one simple reason: To make them smaller so they take up less
house and
greenhouse space when they're brought indoors.
Most growers don't have so much extra indoor growing space that
they can
bring in all those huge full sized plants that have been growing
outdoors all
summer. Fall pruning brings these plants
down to a managable size for winter.
Cold climate growers also don't have the cuttings problem
because all
their plants are grown indoors so the plants from fall cuttings can
winter over
indoors too.
Before going on to the different types of pruning,
there is one simple
rule that applies to all pruning. Always prune directly above an outward facing
bud. (see illustration A) For most
plants this means pruning the plant so all the buds are facing away
from the
center of the plant. In the case of a trellised begonia or one against
a wall,
this means pruning so all the buds face towards the front of the plant.
General Pruning
for Canes
In general practice, young plants are pruned hard and
older plants can
be either pruned hard or light depending on your purposes.
Young plants (well established but only a
year or two old) should be pruned hard.
Hard means down to one or two nodes above the soil. (see
illustration
C) The reason for this is to force the
plant to grow full. When you prune the
plant hard it forces it to send up more new shoots.
The first few years of pruning will determine
how the plant will grow for the rest of its existence.
If you let your plant grow tall and rangy the
first couple of years, then it will always be tall and rangy unless you
start
it over again. With older plants that
have already sent up a good number of canes, drastic pruning isn't as
necessary. You can continue to prune
hard every year if you want short compact begonias.
If you want a nice tall cane, however, you
will have to prune differently. Canes
grow fast but it's hard to prune a cane down to a few inches from the
pot and
expect it to be a 5 foot tall specimen plant that season.
With a mature cane you probably are going to
want to do a light pruning just to keep it in shape. (see illustration
D) The outer canes are pruned fairly low
to
encourage bottom growth so the plant won't be bare at the bottom. The inner canes are pruned at various
heights, taller in the middle and lower with the outer canes. These instructions are for the typical
upright cane. General pruning for
creating hanging basket begonias will be covered separately.
General pruning
for Shrubs and
Semperflorens
Shrubs and semps are pruned slightly differently than
canes. One reason is they generally grow
much
fuller. Shrubs also have an idiosyncracy
in that most stems that are pruned will die back to the soil level. This mostly applies to the larger stemmed and
leaved varieties and to nearly all hairy leaved varieties.
A light pruning to shape will usually not
cause this die back though. Many of the
smaller leaved varieties have so many stems that pruning each stem
individually
can be very time consuming. You can
prune these to a nice shape with hedge shears and then let them grow
out. As a general rule, I prune Semps and
the
small leaved type Shrubs reasonably hard because they grow out so fast
that a
lightly pruned plant becomes overgrown before the end of the season. As they get too tall the stems fall over
leaving the center open. Of course you
can stake but it's much easier to just start out smaller in the spring. Another reason for pruning Semps and the
small leaved shrubs back hard is because as a general rule they bloom
all the
way up the stems so that no matter where you prune the stems to, the
new growth
will still come from the bottom. A
begonia stem can't send out a side branch from a node that bloomed so
if it
blooms all the way up the stem, after you cut it, it has no where to
branch
from except the lowest bud which is usually at the soil line. (see illustration E) With
the larger leaved shrubs and hairy
shrubs, a different pruning technique can be used.
As I said before, with these types, stems
that are cut usually die back to the pot.
You have three choices. You can
prune very lightly to shape to try and avoid the die back.
You can just go ahead and prune hard since
most will die back to there anyway. Or, you can wait for new growth
before
pruning. In the spring most shrubs send
up a flush of new growth from the soil.
At this time, once the new shoots are 6 inches tall or so, you
can prune
out all the old stems, leaving just the new shoots.
This will be less of a shock for the plant
but will have the same effect as a hard pruning. (see illustration F) You can use this method for the semps and
smaller shrubs also. After you have
removed all the old stems, leaving only the new, it will force even
more shoots
to come up, essentially giving you a completely new plant.
This is the method I use for most
shrubs. Another item to consider,
especially with larger stemmed shrubs is that stems pruned above the
pot branch
out ugly. Another reason for cutting
them back to the pot.
Like the large shrubs, many thick-stemmed stems die back to
the soil if
cut. If they don't, they leave an ugly
stump where they branch. They never look
nice after pruning unless the stems are cut completely down to the soil. As a general rule though, don't prune them
too much. Very old, unsightly, or overly
tall stems should be cut out completely but otherwise they should just
be
allowed to grow as they will. All of the
thickstemmed have bare stems so you don't have to worry about forcing
bottom
growth, you can't. They will always have
growth at the tips and be bare at the bottom.
An exception is B.ulmifolia which you should treat as a shrub.
General pruning
for Rhizomatous and
Rexes
Yes, these types can be pruned also.
The upright types can be treated somewhat like the thickstemmed
but you
can force bottom growth on them.
Especially ones like B. crassicaulis, B. carolineifolia, and B.
richii
should be treated like thickstemmed. The
other types can be trimmed back to stay inside the pot.
Any rhizomes that are hanging over the edge of
the pot can be trimmed back an inch or so inside the pot and you can
also trim
out any rhizomes that cross over each other.
As with the other types this will force side growth that will
make your
plant fuller. It isn't as necessary to
prune the rhizomatous as it is with the other types unless you are
trying to
restrict them to a certain size or they get out of shape.
General pruning
for tuberous and
semi-tuberous
Tuberous as a general rule don't need pruning.
All your mistakes die back to the soil every
year and you get to start fresh each spring.
The caudex forming types (semi tuberous) can be pruned to keep
them in
shape if they get too large. Ugly growth
can be trimmed down to the caudex.
General
Pruning Tips and Rules
1.
When pruning, especially canes and shrubs, you should cut out
completely
any stems that have multiple stumps from years of pruning.
This will force up a fresh new stem to
replace the ugly one. I call these older stems stair steppers. (see
illustration G) Also prune out any other
stems that are unsightly.
2.
When pruning, always remove any stems or branches that cross
over each
other. They won't look better with time
and it's best to remove them right away as you see them.
Cut the offending stem back to a bud facing
the other direction or if that isn't possible, cut it to the soil line
and
force it to start over again.
3.
When pruning to make a begonia into a shapely hanging basket you
need to
force only side growth. Any new growth
from the roots is almost always too stiff.
I've heard many new and old growers refer to these strong stems
coming
up in their baskets as sucker growth.
They thought the basket was trying to revert to something else. That isn't true. These
strong shoots are the normal growth of
the plant. (see illustration H) It's the
hanging part that isn't its normal pattern of growth.
Side shoots are always weaker than the
upright shoots of a plant. To keep your
basket as a shapely basket, when these stronger shoots come up from the
base,
prune them down right away to the lowest outward facing bud. This will force side shoots that will be
weaker stems like the rest of your basket.
The reason for cutting them down nearly to the soil is because
you want
them to branch down inside the plant. If
you prune higher, they will branch higher. (see illustration I) This won't create a nice shaped basket. Remember a simple rule, if you want an
upright plant, prune out side growth. If
you want a basket, prune out upright growth.
4.
As I said earlier, always prune to outward facing buds. If you just prune to heighth without regard
to the buds, as they grow out, you will have branches growing every
which way,
crossing over each other. This will
create an unsightly plant. Begonias on a
trellis should be pruned slightly differently.
You aren't concerned about branches crossing over because you
want to
cover the entire trellis. With a
trellised plant, first tie as many branches as possible to the trellis. After you have done that, then you can prune
the loose stems close to the trellis, down to an outward facing bud. When pruning a begonia that will stay against
a wall, in a corner, etc. then prune all the stems so the buds are
facing
towards the front of the plant. This
will force all the stems to grow against and away from the wall instead
of into
wall.
5.
Although I have given you general times for pruning, you can
really
prune a begonia any time of year that you choose. The
problem isn't with the pruning, it's with
the watering afterwards. Since a begonia
doesn't use hardly any water when all the stems are cut back and it has
no
leaves, it can be easy to
overwater. This is one reason why fall
pruning in warm areas can be a problem.
The winter rains can overwater the begonia before it has a
chance to
grow back. In combination with colder
winter temperatures, many begonias can winter kill easily.
No matter what time of year you prune, you
should always be careful with the watering until the begonia gets
growing
again. This is also the reason why many
people have killed begonias when they pruned hard.
It wasn't the pruning, it was the watering.
6.
Safe Pruning. If you are a
hesitant pruner, either because you are a new grower or just haven't
ever
pruned much, there is a safe way for you to learn.
Instead of a light or hard pruning, do it in
stages. This will get you used to doing
the pruning until you learn just how much you can prune off without
killing the
plant. To prune in stages, first just
take tip cuttings like you were taking cuttings to propagate with. This will force the plant to send out side
growth and maybe even new shoots. After
this happens prune a little more and farther down, maybe even a few
stems at a
time if you are really hesitant. Pruning
just parts at a time you will eventually get the begonia cut down to
where you
want it. This will also give you a
chance to see just what happens when you cut a stem, etc.
Also, since you started with the tip
cuttings, these will probably have already rooted and be potted up so
that if
you really make a mistake, you do have the cuttings to fall back on. You really shouldn't have those kinds of
problems though, but better safe than sorry, especially when first
learning.
7.
If you have begonia standards (formed into small trees), they
will
require a little more thought when pruning.
You want to prune them fairly hard because otherwise they'll get
overgrown and not be able to support the long branches.
On the other hand, make sure you leave quite
a few buds so there will be something left to grow out after the
pruning is
done.
8.
You can apply these pruning methods to many of the plants in
your garden
such as roses. I prune my roses and
begonias the same way as a general rule.