Couple of questions regarding the transition of a tree from pot to training box.
Specifically trees bought in ordinary gardening centers planted in ordinary field/planting soil.
What kind of medium should be used in the training pot?
The same as would be used in bonsai pot? Only pumice as if would be collected tree? Something completely different maybe?
Also i can not really figure it out how big training boxes should i build/buy in comparison with diameter of current trunk?
Many thanks for all the answers!
What are the goals of the training container? Are you trying to encourage thickening of the trunk? Are you trying to grow out primary or secondary branches? Are you looking to start refinement?
Basic stuff. At this point i would just like move them out from the regular soil to ensure health and growth.
Would just like to properly prepare trees for next years first styling.
Are the trees rootbound in the nursery container? You can style in the nursery container if you cut some of it away and expose the nebari.
But, as for going into a training container, size-wise its usually best to get close to your final container. If you want the top to grow expansively, go a little bit bigger in all dimensions. In terms of container selection, a rule of thumb is that the height of the container is equal to the thickness of the trunk. This is not something I always follow with training containers, especially for underdeveloped nursery stock.
As for soil, Pumice is good if you are trying to get thickening of the trunk or primary branches. But, a lot of people put things in training containers to start the refinement process. If that’s the goal, you would probably want to use whatever soil mixture you plan on using in the final pot.
As stated above it depends upon your goals. It also depends upon the type of tree.
If it is a tree like a maple that can be bare rooted then training pot/box can be very shallow. I tend to use a pot that is deeper and wider than the optimal bonsai pot since I want the nebari to develop. This often means the depth is about 3 times the trunk diameter and diameter is a bit larger than the spread of the roots after they are trimmed. I normally use a 2-2-1 pumice-lava-akadama mix since I am going to fertilize fairly strongly and save my akadama for my better trees (I sprinkle a bit of the old soil on the top before I add any moss based top dressing). I am planning to plant some 2-3 year old seedlings into flat containers like that with mesh bottoms and am planning to use a 50/50 mix of pumice and screened bark for those, but the goal is to grow them strongly in an environmental where I can get a little better control of the roots and shaping than the ground.
For pines and others than should not be root washed, I clean them down the nebari and then cut off about the bottom half of the roots. Then I loosen the remaining roots digging out the most compacted soil. They end up in a container that will then accommodate the root mass with a little room around the edges. I use a similar 2-2-1 media with some of the original soil mixed in. These can take a couple of years to settle in before an significant styling.
I am fairly aggressive with the initial reporting of nursery stock since I really appreciate a good, spreading nebari on my trees. As a result I lose some trees at this stage. However, most of them were fairly inexpensive and I have very little time and effort invested so it is not a huge loss. I bought a couple of larger and more expensive (at least for me) trees from bonsai growers/nurseries this past year and will do a less aggressive of the procedures above using a media with more akadama since they are already in better soil and further along in their development.
When I want to develop trees bought at a garden centre or nursery I always pot them in a larger than required pot or box. Afterall, if it needs developing it needs to be able to relax and spread a little. I’ve always found basic compost and grit (50/50) to be better than akadama for this purpose. It allows heavy feeding and better water retention than other mixes, so if you can’t get to water it because you are at work this would be better. An aeration layer of pure grit creates the ideal growing atmosphere. When I first started using akadama , pumice, kyriu etc I did comparisons (well I like to know these things!) and when developing and first styling trees, compost and grit won hands down, but when styled and placed in a proper bonsai pot (where growth needs to be restricted and more refined) a mix of akadama, pumice and kyriu were best.