© Copyright 2012
There seem to be many opinions
out there about repotting. You will hear
anything from “I repot mine every year” to “I never repot my trees”. We are going to discuss what I have learned
through my more than four decades of personal experience. Much of it was reinforced by what I learned
from Danny Use. What is written below is
what has been proven to work for me.
The most common sign that you
bonsai, or any plant for that matter, is when you water it seems to just sit on
top of the soil. It may take several
minutes to several hours to soak in.
When this occurs it may not be the correct time to repot the tree. It is critical to take measures to get the
water to the roots. There are many
emergency methods to make this happen.
If you discover that your trees soil is
compacted and water is pooling on the soils surface outside the repotting
season a couple of methods can be used.
One way is to use a sharpened chop stick to penetrate the soil in
several areas. You must ensure that
this is done over the entire surface, otherwise, you will only open up certain
areas and the tree will continue to suffer.
When using this method, it is important to try to penetrate the soil
completely through to the bottom of the pot.
This opens up the soil enough for the roots to utilize the water until
such time that it is safe to repot.
Another method that works better
on larger trees is to use a 1 inch hole saw drill bit to open up certain areas
over the surface. After removing the
debris from each hole, fill them with new soil.
This will ensure that the water will get to the roots all the way to the
bottom of the pot. Again this will buy
you some time until the correct time to repot.
There may be a situation when the
tree is not receiving water or that the tree is staying too wet and you MUST
repot it out of season. This has been
done by me numerous times over the years.
Most conifers can handle this with little or no affect on the tree. Many deciduous trees can as well provided
the correct method is used. The after
care of these trees is crucial as well and can result in death if you don’t
care for them correctly.
When repotting out of season due
to the soil being too wet, you will almost without doubt find that the tree has
suffered from root rot. It is important
in that situation to remove the tree from the pot and use a garden hose spray
nozzle and chop stick to remove as much of the saturated soil as possible. After this has been done carefully examine
the root system for root rot. The roots
will be black and will be decaying all of the way through the root. It may even smell rotten. Use sharp scissors to remove the affected
area from the root mass. It is best to
keep a misting bottle handy to rewet the roots from time to time. When you are sure that all of the damaged
roots have been removed make up a bucket of water with Super Thrive mixed as
directed. While you are preparing the pot
and new soil, allow the roots to soak until you are ready to pot up. After ensuring the tree is securely wired
into the pot and soil has been topped off, water the tree thoroughly using the
Super Thrive solution until the water runs freely from the drainage holes. Place the newly repotted tree in a shaded
area for 2 weeks ensuring that the soil remains fairly moist but not
saturated. After that time you can begin
to acclimate it to the trees required conditions. The tree should show signs of recovery by
In my experience trees purchased
from Brussel’s Bonsai Nursery are extremely susceptible to root rot. Their soil mix may appear to be bone dry even
an inch deep in the soil. This will
tempt the owner to water more than usual. Upon closer examination you will find
that it is saturated deeper, especially at the bottom of the pot where most of
the roots are growing. After 2 years in
their mix the tree will almost always suffer from root rot if not
repotted. Also after 2 years the soil
usually compacts and clogs which will require repotting.
Another technique which is used
for older established trees which have not been repotted regularly is the wedge
technique. This involves removing the
tree from the pot and again carefully inspecting the roots for damage by pest
and disease. When satisfied at
predetermined points around the tree, use a sharp knife of scissors to
carefully cut a wedge from the root ball.
After removing the wedge, inspect the cut area for ragged cuts and
shredded roots. Using sharp scissors
make a fresh clean cut removing the affected root. This method opens up the root system in those
areas and allows fresh soil to be placed in those areas. The tree will have the room to flush out with
new roots resulting in a healthier tree.
Just as described above, water the tree thoroughly using a solution of
If a deciduous tree such as a
Japanese maple, trident maple Chinese elm, zelkova, hornbeam, etc. needs an
emergency repotting, defoliating the tree is recommended. There is one exception to this rule, it is
important NOT to defoliate a beech species.
They only flush out once a year, in the late spring. Defoliating the tree even in an emergency
situation could lead to its demise.
After mid- August, the beech can safely be defoliated. However, it will not leaf out until late the
Normal repotting is much the same
as the emergency methods described above except that when done at the proper
time of year more roots will be removed and more care will be taken to route
and style the roots.
Some rules of thumb are described
in the following sentences. Tropical
trees are to be repotted when the tree is growing the most vigorously. Conifers can be repotted in the fall after
the first frost. If done in the fall it
is important to protect the roots from freezing for at least 6 weeks. Same is true if you repot the conifer in late
winter or early spring. Conifers can
also be repotted in mid –summer during their summer dormancy period. This occurs after their new growth has
hardened off in July and August here in the mid-west. As for deciduous trees, repotting is best
done in the spring just as the buds are beginning to pop.
When you remove any tree from the
pot it is important that you use the proper tools such as root hooks, chop
sticks, etc. in order to unwind and rake the roots to their fullest
length. Carefully inspect all of the
roots for root rot, insects of fungal damage.
Look for and correct if possible crossing or girdling roots. Using sharp root scissors and/or root
cutters, cut back the root mass a reasonable amount. Make an effort to splay the roots out into a
radial pattern if at all possible. This
can be achieved using bamboo chop sticks, wire and props made of wood. Have the desired pot already chosen for the
tree so that the roots may be trimmed back to the proper length for that
pot. As I mentioned earlier, have a
misting bottle handy to keep the roots moist.
When you are ready to pot the
tree, soak the tree in a bucket of Super Thrive solution while preparing the
pot and soil. Please consider the type
of tree when making up a soil mix.
Secure the screen over the
drainage hole(s) and properly install the wires through the bottom of the pot
in order to anchor the tree securely into the pots. Take some of the soil mix you have chosen for
your tree and mix 1:1 with lava rock then pour over the screen completely
covering the bottom of the pot. Then
you can add a thin layer of your soil mix.
Place the tree in the pot ensuring that it is oriented correctly and
positioned properly in the pot. Pour
soil mix over the roots and using the wires installed when preparing the pot
carefully route though and/or over the roots and begin tying the end of the
wire together. Ensure that you twist the
ends of the same wire when stabilizing the tree. Many people make the mistake of twisting the
ends of the separate wired together. Try
to make the tree as stable as possible.
Pour more of the soil mix over
the roots and use a sharpened chop stick to carefully work the soil into the roots. The correct method to achieve this is to
press the stick into the soil at random points and while keeping the chop stick
in one place, roll the top of it in a clockwise or counterclockwise motion. Have extra soil available to pile around the
area where you are working the soil into the roots. Roll the stick until no more soil can be
added. Repeat this at several points
throughout the entire pot. You will
notice that the tree will be much more stable when complete and done
After you are satisfied that the
soil has been worked into all the nooks and crannies you are ready to water
it. Use a Super Thrive solution to water
the tree and wet the roots thoroughly.
This can either be done by immersing the entire pot into a pale of water
or by watering overhead using a watering can or hose. If you use akadama, water the tree until the
water draining for the bottom runs clear.
This washes all of the dust form the particles.
Place the tree in a shaded
location for a couple of weeks then acclimate it to its proper growing
conditions. One thing to note after
repotting is that the tree will use much less water because of the loss of many
of its feeder roots. As the roots and
foliage begins to grow the tree will require more and more water.
With experience you will learn to
know your tree and what to look for.
Many tropical trees need repotted ever year and some every 2 or 3
years. Most deciduous trees can go to 3 to
5 years. And conifers can go for a
decade before repotting. Pay close attention
to the signs that your tree needs repotting and react as needed whatever season
using the methods described above.