Re-potting 2015

One of my Bonsai students asked me to explain the different types of re-potting. I began to explain a little and then thought I should write a blog about this because there are so many different reasons why we re-pot. First let me give a few examples of the different re-potting that one will run into in your bonsai journey.

The first is the Plastic black pot of death re-potting. What is the black pot of death; it's the pot the plant has been repeatedly moved into during its growing life from the nursery. Each time it is moved from a small pot into a little larger, what do you think the odds are that anyone took the time to properly comb out the roots and properly prepared it to be a bonsai....Zero! Sometimes you can almost count the rings or barriers from each re-potting and by the time you get it, it's packed so tight you can't even get a chopstick through it. We will talk about fixing these challenges after we talk about the other re-potting examples.

The second re-potting is Annual and can be either spring re-potting, early summer or autumn re-potting depending on the tree. Either way when you begin re-potting from a growing pot or bonsai training pot into another better growing pot or back into the same pot, it needs to be on some sort of schedule.

The third is Emergency re-potting; for whatever reason you get a bonsai and it is completely root bound in its pot. You can almost hear it screaming ... get me out of here!

The fourth is Slip Re-potting.

The fifth is Re-potting for a Show.

The 6th is Re-potting collected plants two or three years after you have collected them.

Most other re-potting will be a combination of the above, and remember this is just some of the basic information.

Of all these re-potting that one can do, the most important re-potting for the future of your bonsai plant is ... Probably number one? Some may argue that emergency re-potting could be the most important? However removing your plant from a black pot of death is the first step you take toward getting your future bonsai tree healthy

Plastic Black pot of death re-potting: If I look back at some of my mistakes that I made in bonsai it would be “taking a 1 gallon plant and putting it into a nice new glazed pot and calling it a bonsai. I now call these, a stick in a pot.

Technically it is a twig in a pot, but is it really a tree in a pot that represents or mimics nature? No not really. Honestly I may still have one or two of those in my yard. Shame on me!  What I should have done for let’s say a deciduous plant is to cut the roots in half and remove any tap roots, hollow out the center a bit and wash every ounce of old soil from this future bonsai tree. I am sure you have read in my blog where I say “we need to change how this tree thinks”. By removing and hollowing out the roots in the center of the tree we do just that. Then re-potting this little future bonsai tree into a growing pot in a fast draining mix or growing box built for this tree. That one process will help your tree grow faster than had you just shook out the roots and planted it a small glazed pot. A growing pot is used to get tons of feeder roots and should be a bit deeper and wider at first. Get your growing pot full of roots and your nebari growing and then you can move to a smaller pot once you get your bonsai base to the right size. I need to add … if it makes you happy to look at a stick in a glazed pot then by all means do that. There is no bonsai god going to strike you down and take away your chop sticks!

Annual re-potting should be done every year…Hence the name! But seriously annual re-potting (Deciduous) trees in early spring is like you giving your bonsai trees a shot of adrenaline. You do this by combing out the bottom roots and by removing a third to a half of last year’s growth. You then set your deciduous trees flat on the table and comb out the sides and slightly trim the edges and top. You then take your bonsai and wash all the old mix completely out each time you re-pot. This step I believe is the step either most people don’t know about or they just skip?

Deciduous tree sure grow fast ... A crab apple in training

Nothing changes as far as this process goes each year you should re-pot to focus the strength on producing fibrous roots. This should be done before the bonsai plants buds begin to swell. If you wait too long and the buds open, then its best to wait until the leaves completely open and harden off and then re-pot. What type of pot should I use? As above, start with a growing pot either one that you have made or a little bit larger and deeper pot then what your finished tree will need. Again remember we are talking bonsai basics there are always exception to the rule. Annual re-potting in autumn for deciduous trees like Quince is a must for this species. Well, when do I put my tree in a nice fancy glazed pot? We will get to that…

Emergency re-potting: This is done to save the life of the tree. A lot of factors can make you jump to change the mix on a plant dying in front of you. You get a bonsai that has not been re-potted in 5, 10 or 15 years or even longer. Last year I had a Japanese black pine that should not have been alive. It was sticking 9 inches out of the pot

Two tree purchased in 2013 that were emergency re-potted from straight muck...see below picture

How many of you have purchased trees like that? You purchase a tree that is in straight muck, dirt, bark, sand, rock or some other obscenity, like all the potting medium has been washed out. You understand what I am getting at.

Old yucky soil

I am sure all of you have purchased or received a tree on its last leg and had to re-pot it to help revive it, and I am also sure you can think of many other reasons to emergency re-pot. Feel free to leave your comments on my Facebook page. The end goal for all of us is get that tree out of garbage mix and into some fast draining healthy mix to optimize the tree growth and root growth.

What healthy roots should look like

Why focus on root growth so much? Tree health is the number one goal always when re-potting, but there is another very important role your roots play. They hold your plant up. What; that’s right when you get your plants extremely healthy the roots alone will hold your plant in place. You know another secret? When your plants roots are so healthy they fill the pot, this is what we use to tie the plant into the pot. That right we tie the aluminum wire right over the top of the healthy roots insure we don’t damage them but also using them as strength of the tree to help hold the plant in place. Sweet huh!

Slip re-potting: We do a lot of slip potting around here, my students will come up and say I just got this plant but it’s not the right time of year to re-pot it. What should I do? I tell them pull the plant out of the black pot of death, cut barely a quarter off the bottom of the plant, then comb out the sides just a hair.


Put drainage in the bottom and then put the plant back into the black pot of death until it’s time to re-pot that particular tree. Then add as much bonsai mix around the plant to help promote some new side feeder roots until you re-pot it for real. Another time to slip pot is when a pot has broken in some way and you need to put it in another pot fast.


The difference is, you try not to disturb the roots at all and just transfer it to another pot, and then tie it back into the new pot. I am sure you can think of other reasons to slip pot.

Re-potting for a show: This re-potting can use a combination of a few of these above. You worked hard over many years to get your tree to the point of showing it to the general public and now it’s time to shine. Remember above when you asked “when do I put this tree in a nice fancy pot”? Well here you go…First it really depends on when your show is? If your show is near when you do your annual re-potting, then you do your re-potting as normal except to you put your bonsai into the appropriate show or nicer bonsai pot. This gives you an opportunity to really show off that amazing nebari or deadwood feature. If it’s not the time of year to re-pot you would use a more slip pot method. Use your sickle to loosen the edges, cut your aluminum wires and carefully and ever so gently pull your bonsai out of its current pot and pot into a nicer pot. Re-seat it into the new pot and tie it in. This is done in a lot of shows in Japan and then after the shows the plant is returned to its growing pot. Why? The main reason is because these trees in japan at the shows could be sitting in pots worth hundreds of thousands of dollars. I for one would not want that tree sitting in my back yard and have an apprentice or student accidentally damage this old priceless pot.

Preparing this tree for the show...this is what it looked like two years ago. i decided to make it a weeping tree...its getting there.

One more little trick for your show re-potting. Leave about one eighth or one quarter of an inch of room on the very top of your bonsai mix. Why; this allows room for your top dressing or moss.

Re-potting a collected future bonsai plant: Of all the re-pottings, this re-potting is the trickiest. There are many, many factors that go into not only re-potting, but when to do this? It will really depend on the tree. I collected a baby monster oak last year and its growing so fast I could re-pot it this year. But had that plant been a California Juniper I would wait 2 or maybe three years before re-potting. And when I did re-pot, I would remove it from its growing box and find some unique ways to tie it in because collected plants normally do not fill the growing box in a year. Maybe a deciduous plant but not a conifer or juniper.

Urban Yamadori collected maybe 5 years ago....a long way to go. This tree is now wired and i will cut it back this month

It may be years before you see some real root growth. With that said this will be the time that you experience some unique ways to tie your plant in its new container. Unlike a deciduous tree that will fill your pot in a year in the right bonsai mix; your juniper will take a lot, lot longer if ever to fill its growing pot. You may be faced with roots that extend 4 to 6 feet, or a plant that had hardly any roots but the foliage is keeping it alive. I cannot explain all the different tie downs you will use. I can only say they may include 2 by 4 lumber, boxes specifically built for each individual tree collected and lots of wire. Whatever you do…please do not over trim roots, if you trim them at all do a little bit it over time. A great schedule to re-pot collected material is every 3-5 years, remember these plants grow slower.

I hope this information was informative and if anything gets you thinking and asking questions. If you do have questions please stop by Ron Anderson Bonsai Studio and leave me a message.

Great chatting with you!




Written by Ron Anderson — February 05, 2015