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Bonsai Blog

How To: Repotting Bonsai For Beginners

In my last article I touched briefly on the topic of soil and its components for bonsai use. That article was actually a precursor to this one as re-potting time is closer than you think, especially for those of us who live in the southern part of the U.S.

For us we need to be ready by at least the end of Feb. and possibly even sooner, because once you notice the buds starting to swell, you won’t have much time after that for your re-potting.

Hopefully by now you have some kind of an idea of what you’ll be doing for your bonsai soil. Will you be mixing your own using some of the components I listed in last months article, or will you be going online or maybe to a local bonsai vendor to buy an already prepared mix?

Whatever you decide on, in addition to your soil, there will be other things needed to complete your re-potting adventure this Spring. I use the word adventure because many new people to bonsai are really quite nervous about this necessary task and really dread it, when actually it should be something to look forward to each year. Not only does it give you a chance to see first hand what the lifeline of your trees, being the root system, really looks like, but it’s also the time to maybe change that pot for another one you had your eye on lately. Something that really compliments your tree and brings out its full beauty.

Some of the things you should have ready to do a complete re-potting.

These items will include such things as plastic mesh that will be cut to size for the covering of the drainage holes on the bottom of your pots, wire to be used to anchor your tree firmly in the pot so that high winds during the course of the growing season won’t pull the tree out of it’s container, wire cutters to cut this wire, special bonsai wire pliers for twisting the wire to tighten it up, a special rake for raking the roots out on some trees, a hose end sprayer used to soften up the compacted soil if need be, and a soil scoop used to apply the new soil.

The one item I left out is the scissors used for pruning the roots. These can be regular bonsai cutting scissors, or you can use scissors that are considered heavy duty type, just as long as they are very sharp and will hold their edge during the repotting session.

The reason for this is because good clean cuts on the root system is very important, and dull cutters won’t achieve this.

You will also need to have a pair of root cutting pliers for cutting thick roots especially on older larger trees with big extensive root systems.

Well, let’s get started. The trees that I will be mainly using for this repotting article are trident maples. The reason for this is because trident maples are one tree that you will probably have to repot every year like it or not, especially if you live in a very warm climate like I do and where watering is constant and sometimes two or three times a day depending on how dry and hot the summer is and how long they last. For me summer will last right up into the middle of October. The roots on these trees will grow to an incredible length in just one growing season.

Look at this trident and the pot it is growing in. It may be hard to tell the depth of the pot by this picture, but I can tell you it is no more than three inches in depth.

Now look at the roots after they have been raked out. These roots were spiraling around the pot to an almost unbelievable three feet in length, and all in one years growth. Three feet of roots in three inches of soil.

Can you see the importance of root pruning and repotting? Do you think this tree could have survived another year without having its roots pruned and new soil added?

Now don’t get me wrong, what you see with this tree and the amount of root growth, will not be true for every species of tree. There have been times when I pulled a tree out of its pot to find hardly any root growth from the past year.

Some species just don’t grow a lot of roots in one growing season, but you will have to at least familiarize yourself with each species of tree you have by taking the tree out of its pot and looking for yourself to see what it’s doing.

Sorry but there’s no way out of this. If you belong to a local bonsai club, you could ask a fellow member for help possibly, or maybe they will have a special workshop for beginners to learn this important aspect of bonsai.

Here is what the root system should look like after root pruning. Most of the thick roots have been cut off leaving mainly the fine root hairs to do the work of absorbing water and nutrients for the tree.

Here is another trident being repotted and where it was necessary to use the root rake. Many times all that is necessary is to just shake the tree and the roots will just untangle themself and fall out ready to be snipped off. But when this is not the case, then they will have to be either raked out as you see here, or hosed out with your hose end water sprayer.

This next picture shows the pot with a layer of soil and with the wire threaded through the drainage holes and ready for the tree to be added and wired in. Also don’t forget to wash your pot out if you’ll be using the same one. If there are any pathogens present, now is the time to clean them out.

Here is what the tree will look like after it has been wired in the pot. Use your special wiring pliers to grasp the wire and twist it up tight enough to hold the tree securly in place so that it will not be able to come loose and fall out of the pot during high winds.

Since the wire will probably be wrapped around a few thick roots at the base of the trunk in order to secure it, it’s not necessary to tighten it so much that the wire bites into those roots and possibly damaging them.

After that, all that is left is to add the new soil. As you are adding the new soil you must work it in the entire area around the trees root structure. You can either use a chopstick as most people do, or you could use your fingers as others do, myself included, to feel exactly where the soil is going and how loose or compacted it is getting as you work it in.

So there you have it, a basic repotting done in a matter of a few minutes. As long as you are prepared with all the necessary tools and soil right next to you, the job should go by fast and easy.

One thing to keep in mind, especially if this is your first repotting, is that the new soil will be loose and will probably take a few months for it to compact down. Until then you will need to keep a constant eye on the soil for dryness. Since the soil is so loose it will cause more air to be penetrated to the roots and will cause the soil to dry out much faster than if it were more compact, especially if your particle size in your mix is somewhat on the large size.

I hope you will make the most out of your repotting, and most of all have fun doing it.

Note: This article pertains mainly to deciduous tree repotting, with such trees as elms and maples. Other species of trees such as junipers might require a little different approach especially on those junipers whose root system is naturally fine and somewhat delicate. Using both your root rake and or hose end nozzle will need to be done with caution so as not to damage the root system and therefore the overall health of the tree. Japanese Black Pines will also need to have the root system worked in such a way so as to not wash out the necessary mycorrhizae.

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