The repotting thread

[Lazylightningny]

This thread will be about repotting. When do you repot? Why do you repot at that time? Do you repot at other times of the year also? Why? What's the reasoning behind your technique and aftercare? Show us some pictures of your repotting with some explanations. I hope this will be a thread that beginners and experts alike can get something out of. You don't necessarily HAVE to post a picture with your comment.

Here is an American elm volunteer that popped up in my yard 5 years ago and has been in the ground thickening ever since. It was chopped once last year and again earlier this year. It has attained some decent thickness, and buds were lengthening, so I decided to lift it, bare root, and pot up. It had a lot of thick, down-growing roots, which I removed. A good nebari comes from lateral roots, not down-growing roots. In this particular case, I potted in the spring, as buds were lengthening but before they opened. That way, the plant expends as much of its stored energy toward the buds as it can before I drastically reduced the roots. This will delay the opening of the leaves, but if you wait until the leaves open, I've found that the tree can't support the new leaves after roots have been drastically reduced. It was wired into this plastic training pot in a mixture of equal parts of sorted and sifted lava, pumice, and akadama. It was placed back in the sun (or what there is of it lately) and watered once every day. This is my typical aftercare, unless I do a summer repot and the temps are over 90 degrees F.

 

[Wires_Guy_wires]

I repot in spring mostly. If I have the time. Otherwise I do it later.
Either in summer, fall or winter. I do this because I like to learn and I'm comfortable killing a 3 euro mugo pine. But ever since I got the hang of conifers, it's rarely a death sentence. I haven't killed a single one unintentionally in the past two years.
I'm also a firm believer of not cutting off any roots the first time they go into training or bonsai pots. I am convinced that roots grow from the tips, but to get them to make new tips closer to the base, it doesn't help to cut the existing one off at the end. Apical dominance also happens to occur in roots; cut a tip, and two new tips will form. If the pathway of water is too long for that root, then it'll probably produce finer roots closer to the trunk. Not because it's cut, but because the tree wants to. I think this idea might be the key as to why the trees don't die on me anymore, even after bare rooting.
Yes, those long ropes will die. Yes, they'll fill up space in the pot. Once that's happening, I can water less often since they keep a lot of moisture around.
A couple of my scots pines require yearly repots because they colonize the soil so fast. Some might call my technique a bad practice, but I haven't seen those bad results yet. So I'm sticking with it.

When I'm overly aggressive on the roots, I supply 3mg/L of IBA on the first couple of waterings.

Aftercare in my case is using sphagnum on top of the soil and keeping an eye out. It either lives, or I was too aggressive and I'll probably learn after the next time. But judging from the past two years, I think most of my techniques are pretty conservative.

 

[Stan Kengai]

The two most common mistakes I see (and used to do myself) in repotting are repotting too frequently and not removing enough roots. I'm not talking about when transitioning from nursery containers or poor soil or to correct root problems. But once a plant is in good bonsai soil, most plant (even shohin) can go at least 2 seasons between repottings, obviously more for larger plants. And when you do repot, 70% of the root mass or more can be removed on most plants. When I found Haruyosi's blog several years ago, I was astonished by the amount of root reduction he did, including on pines. So I tried it myself and haven't had any losses or setbacks. I wish I had known this years ago.

 

[Shibui]

The two most common mistakes I see (and used to do myself) in repotting are repotting too frequently and not removing enough roots. I'm not talking about when transitioning from nursery containers or poor soil or to correct root problems. But once a plant is in good bonsai soil, most plant (even shohin) can go at least 2 seasons between repottings, obviously more for larger plants. And when you do repot, 70% of the root mass or more can be removed on most plants. When I found Haruyosi's blog several years ago, I was astonished by the amount of root reduction he did, including on pines. So I tried it myself and haven't had any losses or setbacks. I wish I had known this years ago.

As with any generalization there will be exceptions.
I agree with taking off more roots with most trees.
There are some species that have prolific root growth and need regular root pruning or slip potting just to keep them alive when young. Banksias are one genus i have found do far better when repotted annually while they are young. Root growth is prolific and extremely fine and matted. By the second summer most pots are so crammed with roots that it becomes very difficult to water and trees decline. Annual repotting or slip potting allows room for air and water to keep them healthy.
I also find that many younger shohin, especially trident maples do better when repotted annually. These photos of a small trident after just 7 months in the pot. Should I have left it another year?






I'm not at all sure that root pruning has an adverse effect on most bonsai. I have noted that my bonsai grow considerably faster and better in the summer following repotting. How can that be if root pruning causes a setback?
Trident maples in my grow beds are now lifted and SEVERELY ( way more than 70%) root pruned EVERY winter. This gives me great regrowth and even better root ramification and nebari.

As always everyone is free to follow their own path in bonsai. Just need to be aware that there are other legitimate paths for others to travel to the same destination.

 

[Stan Kengai]

As with any generalization there will be exceptions.
I agree with taking off more roots with most trees.
There are some species that have prolific root growth and need regular root pruning or slip potting just to keep them alive when young. Banksias are one genus i have found do far better when repotted annually while they are young. Root growth is prolific and extremely fine and matted. By the second summer most pots are so crammed with roots that it becomes very difficult to water and trees decline. Annual repotting or slip potting allows room for air and water to keep them healthy.
I also find that many younger shohin, especially trident maples do better when repotted annually. These photos of a small trident after just 7 months in the pot. Should I have left it another year?
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I'm not at all sure that root pruning has an adverse effect on most bonsai. I have noted that my bonsai grow considerably faster and better in the summer following repotting. How can that be if root pruning causes a setback?
Trident maples in my grow beds are now lifted and SEVERELY ( way more than 70%) root pruned EVERY winter. This gives me great regrowth and even better root ramification and nebari.

As always everyone is free to follow their own path in bonsai. Just need to be aware that there are other legitimate paths for others to travel to the same destination.

I agree that there are always exceptions, that's why I said "most plants." There are also environmental conditions that may factor into it as well. Plants growing in arid climates are probably going to make more roots than the same plant growing in a humid climate.
I'm not adverse to root pruning. The reason I like going longer between repotting is that you can get finer, more delicate growth with smaller leaves and shorter internodes.

 

[Vance Wood]

In bonsai culture it is critical to encourage and develop a fine root system. This is not an easy thing to do if the tree in your hands is a nursery grown tree with an over grown root system made of a lot of large roots. With the exception of the large surface roots (nebari) that are favored for design puirposes, in nature large roots are anchors needed to keep the tree in the ground. In bonsai it is again critical that the support function of a root system must be replaced on a regular basis by the encouragement of an abundance of fine usable feeder roots over the large and numerically few, support roots that actually do not do anything other than take up space. Every repot should concentrate on removing and replacing the large support roots and developing the fine feeder roots that by their numbers will perform the same support function. This is how a large fat trunked bonsai can be grown in a shallow bonsai pot.

 

[Lazylightningny]

In some cases, roots can be drastically reduced. Azaleas produce a lot of fine roots. In this case, I reduced the root ball of this nursery purchase enough to fit into this 4" wide container potted up in straight kanuma. The tree won't bud out now for a good month, and I won't prune any branches this year so the tree has a chance to recover from being brutalized. It will do fine though, and next year I can start to prune to ramify branches. Something like this could never be done to other trees such as pines. Aftercare includes placing the tree back into sunlight and watering daily. I won't fertilize until I see buds moving. When hot weather hits, it will be placed into semi-shade and watered more frequently. For azaleas, I only repot in the spring and not summer since they are heat sensitive. This tree won't flower for several years now because I will prune the branches each late winter/early spring until I get some decent ramification. I could also prune after flowering, but I don't want to waste the tree's energy on flowers yet.

 

[Shibui]

I only repot in the spring and not summer since they are heat sensitive.

Each to their own. I have dug azaleas at all times of the year including mid summer and I would bet that my midsummer is a lot hotter than Downstate New York. My collected azaleas probably have far more severe root pruning than any bonsai repot and those mid summer collections just continued to grow.

The reason I like going longer between repotting is that you can get finer, more delicate growth with smaller leaves and shorter internodes.

I see that I missed your point. I agree that less frequent repotting aids in shorter internodes and better ramification. This seems to be as a result of the trees being less vigorous. Seems to point to more regular repotting and root pruning helps to stimulate growth. Many still convinced that root pruning is detrimental to the health of plants.
The real benefit of less repotting is not plant health and vigor but in reduced vigor leading to more manageable growth and ramification.

 

[Mesmonter]

Hey, thanks for starting this thread on repotting! It's always fascinating to see how different folks approach this aspect of bonsai care. Your American elm looks like it's coming along nicely. I admire your attention to detail, especially with the roots and timing of the repotting process. It's clear you've put a lot of thought into it.