Here I am, holding up a trident
maple that has just been removed from its pot and root-pruned in preparation for
repotting. The rootball is becoming flatter through the years, with feeder roots
being removed from the center. Feeder roots at the outside encourage the nebari
to spread. The grey areas are cut paste protecting newly removed knobs. Gradual
work over many years will continue to improve this nebari.
Repotting techniques
The how of repotting is as important as
the why. Here we want to discuss proper repotting technique as a means to
increase the vigor and health of your trees, to improve their aesthetic value,
and to continually increase their value to you and others. Proper repotting
includes proper root-pruning technique and a beneficial
soil mix.
Materials needed
These
are some of the tools needed to properly repot your tree. First and foremost is
an adequate supply of proper soil. Above the small pile of soil mix you see a
sieve, with three sizes of screens. I also use a homemade sieve made with common
window screen to sieve the smallest particles. Just to the right (a little
harder to see) is a pair of angled-tip tweezers, some chopsticks, and a potting
saw. On the turntable is a Japanese brush used to smooth the soil, and directly
below it is an example of the plastic screening used to cover the holes in your
bonsai pot. On the upper right are standard wire cutters, wire pliers, a pair of
shears dedicated to root work, and a repotting rake. A heavy restaurant grade
fork, bent in a vise, works well as a root rake, but these are very inexpensive
and well worth the investment. Just above these is the mason's margin trowel I
use to tamp my soil. Its blade is really too long for this work but it can
easily be ground down to a more useful size and shape. And at bottom right is
the coil of wire I will use to attach the screens to the pot and wire the tree
into the pot.
Preparing the Pot
The very first step for repotting must be the preparation of the
soil and the pot. Nothing could be worse than to have a bare-root tree waiting
for you to find and prepare your pot.
Your pot should be clean
and free of residue from previous use. Remove the old screens and wires, these
can harbor insect eggs and disease. If the previous resident of the pot died of
mysterious causes, you should also sanitize the pot with a mild solution of
bleach and water. Cut pieces of your screen that will be larger than the holes.
This is absolutely the wrong place to try to economize. Screens that are almost
too small are too small. They will pull through the holes and allow your soil to
escape. Screen is so inexpensive that the tiny bit more you use may as well be
free.
This
photo shows a pot with screens and tie wires in place, ready to receive its
first layer of soil. This is the proper way to secure a tree in a pot with four
holes. For three holes, two wires will be used, with one end of each coming
through one hole and the other ends through the remaining holes. With only
two holes, both wires pass through both holes. Notice that the tie wires are at
the innermost points of the holes. When the wires are tightened, they will draw
up to these points anyway. This prevents dragging your screens or leaving too
much slack. Also notice the way the clips hold the screens, at 90 degrees from
the direction of the tie wires. This prevents the screens from moving back and
forth too much.
Now
we see the pot with a drainage layer of pumice in the bottom. In a very shallow
pot, this will be a very thin layer, perhaps only one granule thick. In any
event, this is not a very deep layer. In this case, it was about 3/8". There has
been a great deal of heat about the efficacy of drainage layers in bonsai pots.
It is claimed that water can perch in the smaller soil above it leading to soggy
soil. However, perched water tables are found in nature only in groundwater
situations with a constant flow of water. Bonsai soil is not garden soil,
and we do not water our trees constantly. Therefore, I elect to follow the
teachings of my sensei and virtually all the Japanese bonsai community and use a
drainage layer.
Preparing Your Tree (Nursery Stock)
The
first step is to remove your tree from its nursery pot. This is easiest done by
flexing the pot either with your hands or, in extremely rootbound situations,
with a mallet or perhaps even cutting it off. Once your tree is out of its deep
pot, it is time to remove a good portion of the bottom of the root mass. In the
case of a juniper, it is a simple matter to cut through the fibrous rootball.
This will give you a more workable size as you manipulate the tree.
Now
is the time to work on your tree's roots. Many people use a chopstick, or worse,
a large root hook to "comb" out the roots. This is extremely hard on your tree,
and does damage to the roots you want to keep. When combing out the surface of
the root pad, use an angled pair of tweezers to gently work the soil and roots
away from the trunk. This will expose any surface roots and let you decide on a
front for your tree. Follow this step with combing out the bottom roots using a
small root-rake, not the root hooks you see so often. Comb the roots, then cut
them flat to the soil, and repeat.
Bare-rooting conifers is
not recommended, as it can kill the tree. However, all the field soil needs to
be removed, so how is this done? Bare-root half the rootball in the first
potting, and the other half the next time. The chopsticks in the roots are a
guide to show where we wanted to stop bare-rooting. The remainder of the
rootball will be lightly combed out, removing any circling roots.
Tying Your Tree Into the Pot
It has been suggested in certain places on the internet that
tying your tree into the pot is not necessary, or that one should use cotton
twine that will decompose as time goes on. Tying the tree into the pot
serves the purpose of staking a landscape tree. Without the stability
afforded by tying in, your tree will fail to thrive. The most important
thing about growing bonsai is that they be healthy and vigorous, so that you
can train them successfully. Therefore, tie them in with wire. The roots and
trunk will be held fast, and can grow well. Roots that are constantly being
jostled will never really take hold.
