Bonsai by Fields, LLC    

Since 1983 - Located in Greenwood, IN - (317) 439-0678




© 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. 


Emergency Repotting

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 that time.  

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 Super Thrive.

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 following spring.

Normal Repotting

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 properly. 

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.   

Products & Services
Tutorials, etc.
About Us
Guest Book