Moving from nursery container to grow box. What size to build?

[Matt3839]

This coming spring I’m going to be moving a lot of trees to grow boxes and I’m a little unclear about what size to build.
the trees (Hinoki and cryptomeria) are coming out of nursery pots so I’ll be exposing nebari and doing some root pruning at the bottom after but still leaving native soil at first.

If I were to take a tree that’s in a 5 gallon container - assuming I prune some roots and expose nebari would I want to do a grow box maybe 2/3 of the volume? 1/2?

I know we’re a ways off from spring but I thought it would be a nice winter project and I have 7 or 8 boxes to make. And maybe able to get some free lumber from a construction site before it gets tossed so any guidance is very appreciated.

 

[Shibui]

What is the aim of transferring to grow boxes? 5 gallon container is already pretty big so either the trees are quite large or they will have plenty of room to grow in those pots.
Going down in size would assume your trees have finished growing and you're moving on to developing apex and branching by slowing growth?

I'm not sure there's any rule of thumb on sizing a development box. Appropriate size probably has less to do with the current container size and more about the current size of the tree, the species and what you want to achieve.

 

[Matt3839]

What is the aim of transferring to grow boxes? 5 gallon container is already pretty big so either the trees are quite large or they will have plenty of room to grow in those pots.
Going down in size would assume your trees have finished growing and you're moving on to developing apex and branching by slowing growth?

I'm not sure there's any rule of thumb on sizing a development box. Appropriate size probably has less to do with the current container size and more about the current size of the tree, the species and what you want to achieve.

So my main goals are:
A) transferring or at least partially transferring to a bonsai substrate
B) thicken trunk but not looking for gain in height.
C) create more fine roots
D) expose nebari on trees so I can start to think about design. So they’re going to need to be repotted anyways.



I’m pretty happy with the few trees I put into pond baskets when they arrived bare rooted, and so I’d like to also repot my other nursery stock stuff. But the pond baskets are too small I think, plus I do like the look of a wood grow box vs plastic

Hope that all helps. Open to thoughts!

 

[Shibui]

A, C and D are good reasons to transplant to new soil and will probably be facilitated by a smaller container.
Trees will grow in bonsai substrate, even in larger containers but transferring to bonsai substrate is only really important when moving to smaller containers. Doesn't matter so much in larger grow containers and can usually wait until development is done.
I have not noticed that different soil types or different containers have significant bearing on fine roots. My experience is that creating fine roots is best achieved through judicious root pruning.
Exposing nebari is a vital first step to design but we don't have to go full transplant to do that. Just raking off the surface soil is usually enough to get a good enough look at nebari.

I think B - thickening trunk but restricting height might be counterproductive unless you plan on a ver r r ry long project. Trunk thickening seems to be directly linked to growth - either apex or sacrifice branches. Smaller container will usually restrict growth of either or both which will normally result in less thickening. larger containers for thickening, smaller containers to restrict growth for developing better proportioned branching with closer internodes.

Unfortunately, we don't seem to be able to get everything we want all at the same time when growing trees.

Wood V plastic is also a valid reason but has no relevance on size.

I would be making boxes that are suit the size of the tree but are also convenient to house and to move. In La you won't need to overwinter but will probably need to rotate trees to get good all round growth. You'll also want to move then occasionally for trimming, styling, etc and may even want to take some to workshops, etc so make them manageable if possible.

 

[Matt3839]

A, C and D are good reasons to transplant to new soil and will probably be facilitated by a smaller container.
Trees will grow in bonsai substrate, even in larger containers but transferring to bonsai substrate is only really important when moving to smaller containers. Doesn't matter so much in larger grow containers and can usually wait until development is done.
I have not noticed that different soil types or different containers have significant bearing on fine roots. My experience is that creating fine roots is best achieved through judicious root pruning.
Exposing nebari is a vital first step to design but we don't have to go full transplant to do that. Just raking off the surface soil is usually enough to get a good enough look at nebari.

I think B - thickening trunk but restricting height might be counterproductive unless you plan on a ver r r ry long project. Trunk thickening seems to be directly linked to growth - either apex or sacrifice branches. Smaller container will usually restrict growth of either or both which will normally result in less thickening. larger containers for thickening, smaller containers to restrict growth for developing better proportioned branching with closer internodes.

Unfortunately, we don't seem to be able to get everything we want all at the same time when growing trees.

Wood V plastic is also a valid reason but has no relevance on size.

I would be making boxes that are suit the size of the tree but are also convenient to house and to move. In La you won't need to overwinter but will probably need to rotate trees to get good all round growth. You'll also want to move then occasionally for trimming, styling, etc and may even want to take some to workshops, etc so make them manageable if possible.

Thanks so much for your detailed reply. A lot of things for me to consider.

Part of the reason I’d also like to repot is on some of my trees- hinoki’s - which are in 5 gallon containers and about 4 feet tall, are that they have so much surface roots I can’t expose the nebari without doing a repot. The surface roots are so plentiful you can’t scrape the soil away In the pot. I’ve posted a photo of the tree. So while I’m repotting I feel like a grow box would be a nice direction to take. I’m leaning towards a 14x14x 5 to transition from a 5 gallon pot. Assuming I’ll take off 1/4 of the top soil to dig out the nebari and a tiny bit on bottom. From what I’m reading, wider is better than deeper.

I could do my potting soil pumice mix of 70-30 which my cryptomerias are are all happy in, but sometimes I do worry about how long they stay wet. not as big of an issue with a shallower pots but transitioning to bonsai substrate is inevitable and I have two bags of aoki blend I got for a good deal so I figure I might as well use them if there are no drawbacks.

Anyways thanks for educating and advice. Please do let me know if you see anything wrong with my plan. And noted about cutting the apex too early. Thank you

 

[Shibui]

Your 14x14x5 works out to 4.2 gal (if I've done the math correctly) so that's not much of a reduction in volume. You should still get good growth in those boxes.
Shallow containers are often recommended to develop a shallow root system for eventual transfer into a bonsai tray. Not sure that I totally agree with that as you'll still need to reduce the root ball depth by at least half so that's not a great deal better than doing the reduction from a deeper container and I suspect the lateral roots will also need substantial reduction from 14" to fit the pot spread too. In any case, I've never had any problem moving trees from deeper containers straight to bonsai pots but people are welcome to follow the path they feel most comfortable with.

I could do my potting soil pumice mix of 70-30 which my cryptomerias are are all happy in, but sometimes I do worry about how long they stay wet. not as big of an issue with a shallower pots but transitioning to bonsai substrate is inevitable and I have two bags of aoki blend I got for a good deal so I figure I might as well use them if there are no drawbacks.

Getting all your trees into similar mix definitely helps simplify watering and is something I recommend. You will probably find that shallower containers dry out quicker than deeper. I have not actually checked closely but suspect that wood containers might also dry quicker than plastic nursery pots as the wood is able to absorb and transmit water through to the air.

Will be interested to see your grow box design and materials so please consider posting some shots of construction and planting when you get to that.

 

[Matt3839]

Your 14x14x5 works out to 4.2 gal (if I've done the math correctly) so that's not much of a reduction in volume. You should still get good growth in those boxes.
Shallow containers are often recommended to develop a shallow root system for eventual transfer into a bonsai tray. Not sure that I totally agree with that as you'll still need to reduce the root ball depth by at least half so that's not a great deal better than doing the reduction from a deeper container and I suspect the lateral roots will also need substantial reduction from 14" to fit the pot spread too. In any case, I've never had any problem moving trees from deeper containers straight to bonsai pots but people are welcome to follow the path they feel most comfortable with.


Getting all your trees into similar mix definitely helps simplify watering and is something I recommend. You will probably find that shallower containers dry out quicker than deeper. I have not actually checked closely but suspect that wood containers might also dry quicker than plastic nursery pots as the wood is able to absorb and transmit water through to the air.

Will be interested to see your grow box design and materials so please consider posting some shots of construction and planting when you get to that.

Hey @Shibui, you raised some great points. I don’t think it’s a big reduction in volume but thinking of doing only 4 inches high for the boxes potentially, and I’ll definitely need to reduce the lateral root spread. I’m hesitant about doing a huge reduction to fit into a bonsai pot straight away. Hence the slightly oversized wood box plan.

I do have one more question for you if you have time.

I’ve been reading through several soil threads for developing trees and unfortunately they ALWAYS get derailed by page 2 and turn into an akadama debate.

My hinoki’s will go into a bonsai substrate when repotted in boxes but I do have several cryptomerias are still in very early development, 3 in pots and 1 in a pond basket. The one in a pond basket was potted in 70-30 potting soil pumice mix and is growing quicker than the other two in nursery containers, so I was planning to transfer the others to pond baskets as well.

Do you think it’s worth changing the substrate to a bonsai substrate when I repot at this point? Is there any gained benefits from the extra cost of bonsai substrate vs just planting in cheap soil/pumice mix for a very young tree? I know i could be opening a can of worms but keep in mind it’s for trees in pretty early development.
If I had a yard I’d stick them in the ground in a heartbeat but unfortunately such is life.

 

[Matt3839]

or perhaps pine bark pumice mix instead of potting soil

 

[Shibui]

Is there any gained benefits from the extra cost of bonsai substrate vs just planting in cheap soil/pumice mix for a very young tree?

I do not find much difference but that will depend on how you care for your trees.
If you find trees grow better in bonsai mix then it may be worth the extra cost.
There's no problem changing soil type when you are ready to make the change to smaller bonsai pots so starting in bonsai mix is not necessary from a horticulture view.

 

[Matt3839]

I do not find much difference but that will depend on how you care for your trees.
If you find trees grow better in bonsai mix then it may be worth the extra cost.
There's no problem changing soil type when you are ready to make the change to smaller bonsai pots so starting in bonsai mix is not necessary from a horticulture view.

Makes sense. Yeah I know you did suggest organic before. After doing some more research I came to the conclusion I’ll probably do a pine fines and pumice mix which will be more cost effective and may promote quicker or as quick growth in the boxes for trees still in very early development.