Sizing a Grow Box

[The Warm Canuck]

I have an Amur Maple that I bought at a nursery this fall and planted in the ground for over the winter. I want to get it out of the ground this spring and into a screened grow box, ala Vance Wood style, for further development. It had a large root mass at planting, as it was in a 5gal pot, that I just split potted it into the ground. The roots are going to require a fair amount of reduction.

How does one estimate the size of the box that will be required? I want to be able to make the box before taking it out of the ground and doing the root work, so I'm not rushing to make the box.

 

[Colorado]

I would just make the box after you do the root work. Should only take 15-30 minutes to make the box IF you have all the materials prepared, work space set up and ready to go, and a basic plan for how you’re going to build it.

That way you know you have a box that is going to be the size you need, rather than guessing and ending up too small or too large.

If you are intent on making the box first, I’d just use the 5 gallon container diameter for your interior dimension of the box. Have fun!

 

[penumbra]

I agree with all the above^^^^
When I was placing trees in grow boxes a couple years ago, I made half a dozen boxes in different sizes.

 

[Wulfskaar]

FYI... some basic measurements for volume of soil.

VERY ROUGH ESTIMATE:
12" x 12" x 6" = 3.74 US Gallons

I used that size for a couple grow boxes I made because I got a couple 3.5 gallon bags of soil from bonsaijack.com. They basically fit really well into that size of box. You can edit the size of your box, but it's good to know how much soil it will require.

 

[rockm]

I have an Amur Maple that I bought at a nursery this fall and planted in the ground for over the winter. I want to get it out of the ground this spring and into a screened grow box, ala Vance Wood style, for further development. It had a large root mass at planting, as it was in a 5gal pot, that I just split potted it into the ground. The roots are going to require a fair amount of reduction.

How does one estimate the size of the box that will be required? I want to be able to make the box before taking it out of the ground and doing the root work, so I'm not rushing to make the box.

The size of the grow box depends on the root mass you have or want to have.

If this were my five gallon amur--I'd also reckon on a 12x12x6 box and reduce the roots and top accordingly.

Amur are tough trees and can take substantial reduction. This spring, before bud break, I'd saw off the bottom two thirds of the root mass right out of the five gallon container. I'd then chop the trunk at about where you want the final height to be...rake out the rest of the roots, eliminate the bad and/or uncooperative ones, then put in the grow box and back fill with bonsai soil.

 

[Pitoon]

Whatever size you decide upon....make sure you use standard lumber sizes to save time on unnecessary cutting. I make mine 12x12x3.5 using 1"x 4"x 8' boards.

 

[The Warm Canuck]

Here's a pick of the tree, its 4' tall right now the root ball is probably 16" across.

The trunks are about a 1-1/4 each. I want to thicken them more.

 

[The Warm Canuck]

. I'd then chop the trunk at about where you want the final height to be...

Any advice on what branches I should cut or keep?

 

[John P.]

I’d leave one of the trunks untouched to let it add more size and cut back the other in order to lose some slingshot vibes from both trunks being the same size.

 

[Deep Sea Diver]

Who you calling a Slingshot!?


Cheers
DSD sends
PS Gotta love good woodworking!

 

[sorce]

Yeah, it seems cutting the thick stuff off the left one, and leaving the right untouched for now should be good.

I'm happy you're talking screened box!

My little clump of seedling Amurs went from lead thick to a little over pencil thick in, shit, 1.5 years? In one of my small 4x4in baskets.

They tend to make good use of soil, I'd like to see you start small, and increase the size like nurseries do pots, it will aid in keeping a good core of feeders.

Sorce

 

[The Warm Canuck]

Yeah, it seems cutting the thick stuff off the left one, and leaving the right untouched for now should be good.

I'm happy you're talking screened box!

My little clump of seedling Amurs went from lead thick to a little over pencil thick in, shit, 1.5 years? In one of my small 4x4in baskets.

They tend to make good use of soil, I'd like to see you start small, and increase the size like nurseries do pots, it will aid in keeping a good core of feeders.

Sorce

I agree, I don't want it to have the slingshot look! haha The left one is actually thicker, I'll have to cut some of the top just to make it manageable when repotting.

I'm really excited to try the screened box. I'll start with 12x12x6 as per @rockm 's advice, and pot up as it goes. Or are you saying to even start smaller than that?

 

[The Warm Canuck]

What do you guys think? I guess die back is a problem on these, so I'm a little nervous with cutting the right hand trunk so low.

For reference the right hand cut would be 6" off the ground.

 

[rockm]

I agree, I don't want it to have the slingshot look! haha The left one is actually thicker, I'll have to cut some of the top just to make it manageable when repotting.

I'm really excited to try the screened box. I'll start with 12x12x6 as per @rockm 's advice, and pot up as it goes. Or are you saying to even start smaller than that?

A rule of thumb for potting newly collected or reduced stock is to get them into the smallest container possible. That is because the larger the container, the more soil it holds and the more water that soil holds. That excess soil tends to stay wet since newly cut roots aren't using it. That constant wet can rot roots.

That said, you want a container that's big enough for the tree to push a lot of new roots. A balance is required. Given the size and vigor of your amur, I'd say a root reduction that get is juuuuust into a 12X12x6 container should work pretty well..

Also, I wouldn't really consider this a twin trunk candidate, even though it has two trunks. That's the problem, neither is larger than the other--they're the same. A twin trunk or "mother daughter" composition should have one tree (typically the larger and thicker) dominant over a smaller one. That creates visual tension. Uniform trunk size (at soil level) doesn't do that. I'd get rid of one and work with the other. Which one depends greatly on where the best surface roots are...

 

[sorce]

Since the circled part will become problematic faster, I'd reduce that, and just keep the right from getting that way with some smaller cuts and future diligence.

The problem with a large basket, right is your airpruning will take place outside of where you future pot will be, so all them roots will be cut off.

By slowly increasing the size, left, or even just keeping it smaller straight through, you'll have the masses of feeders close to the trunk where they can remain useful.



Sorce

 

[leatherback]

This spring, before bud break, I'd saw off the bottom two thirds of the root mass right out of the five gallon container.

Word of warning from someone stupid speaking of experience.. The nebari is NOT always at the top of the pot. So take out of the pot. Dig down to find the nebari (Not the first tiny root, but significant roots) then cut the remaining 2/3 off.

 

[The Warm Canuck]

Since the circled part will become problematic faster, I'd reduce that, and just keep the right from getting that way with some smaller cuts and future diligence.

The problem with a large basket, right is your airpruning will take place outside of where you future pot will be, so all them roots will be cut off.

By slowly increasing the size, left, or even just keeping it smaller straight through, you'll have the masses of feeders close to the trunk where they can remain useful.

View attachment 412356

Sorce

I like it, that's what I'll do! You're right, that left side would be a problem.

I like your logic on the air pruning basket. I'm going to squeeze it in a 12x12 as per @rockm and try not to pot up any higher than that, cutting back the thicker roots on the next repot, hopefully having them replaced with feeders.

Also, I wouldn't really consider this a twin trunk candidate, even though it has two trunks. That's the problem, neither is larger than the other--they're the same. A twin trunk or "mother daughter" composition should have one tree (typically the larger and thicker) dominant over a smaller one. That creates visual tension. Uniform trunk size (at soil level) doesn't do that. I'd get rid of one and work with the other. Which one depends greatly on where the best surface roots are...

I appreciate your opinion, and I understand what you mean but I like the look of it even though it may not be Bonsai perfect. Also as it is a Amur, I worry about die back on cutting back one of the trunks so low.

Word of warning from someone stupid speaking of experience.. The nebari is NOT always at the top of the pot. So take out of the pot. Dig down to find the nebari (Not the first tiny root, but significant roots) then cut the remaining 2/3 off.

Thanks for the advice, I'll be sure to dig down and look for the nebari, than cut the 2/3 off. I think there's some misunderstanding though, this tree was planted in the ground in the fall, it's not in a container, but I did plant it on a tile, so I know how deep the "bottom" of the pot would have been.

 

[River's Edge]

Any advice on what branches I should cut or keep?

Perhaps one should separate the questions.
1.cutting or keeping branches is dependant on wether you wish to develop the trunk further and require sacrifice leaders or branches for that purpose.
2. Or are you just cutting back to introduce taper and change of direction, essentially happy with the overall thickness of the base.
3. Grow box size is also an independent question, the answer based on the stage of root ball development and the time you wish to take to get to a root ball suitable for a bonsai pot.
4. This is a recently acquired tree from a nursery so I would plan on dealing with the growth and development of the root ball structure first. This will be aided by additional sacrifice leaders and branches providing additional foliage during the growing season. So I would modify my cut back/pruning plans to assist the primary goal.
5. Because it is a maple the shallower and wider format is a good choice. 12 by 12 by 3 1/2 is ok but from my experience I get faster development of root ball and trunk thickening with a bit larger size. Anderson flat deep propagation tray. 15 by 15 by 7. I simply do not fill the tray with soil, using the 3 1/2 to 4 inch depth. I allow for a shallow drainage layer.
6. The maples developed in the Anderson Flats grow faster than the ones in the smaller wooden grow boxes. Situated in the same location with the same care! This could be due to the better aeration and drainage of the Anderson flat. My grow boxes have good drainage but not the same as the grid on the bottom of an Anderson flat.
7. Be careful with screened grow boxes they can have the same draw backs as colanders and pond baskets. Drying out too quickly!

 

[The Warm Canuck]

Perhaps one should separate the questions.
1.cutting or keeping branches is dependant on wether you wish to develop the trunk further and require sacrifice leaders or branches for that purpose.
2. Or are you just cutting back to introduce taper and change of direction, essentially happy with the overall thickness of the base.
3. Grow box size is also an independent question, the answer based on the stage of root ball development and the time you wish to take to get to a root ball suitable for a bonsai pot.
4. This is a recently acquired tree from a nursery so I would plan on dealing with the growth and development of the root ball structure first. This will be aided by additional sacrifice leaders and branches providing additional foliage during the growing season. So I would modify my cut back/pruning plans to assist the primary goal.
5. Because it is a maple the shallower and wider format is a good choice. 12 by 12 by 3 1/2 is ok but from my experience I get faster development of root ball and trunk thickening with a bit larger size. Anderson flat deep propagation tray. 15 by 15 by 7. I simply do not fill the tray with soil, using the 3 1/2 to 4 inch depth. I allow for a shallow drainage layer.
6. The maples developed in the Anderson Flats grow faster than the ones in the smaller wooden grow boxes. Situated in the same location with the same care! This could be due to the better aeration and drainage of the Anderson flat. My grow boxes have good drainage but not the same as the grid on the bottom of an Anderson flat.
7. Be careful with screened grow boxes they can have the same draw backs as colanders and pond baskets. Drying out too quickly!

I appreciate your insight, my Island friend.

My primary concern at this point is to get the tree out of the ground. I am happy with the size of the lower trunk, but I wouldn't mind developing the right hand trunk further to create a noticeable difference in size to the left hand trunk. Yes, you have made me realize that I should keep the majority of the foliage intact to focus growth in the root ball (at least on the right hand side, I do want to reduce growth on the left side and get rid of the problem area @sorce identified). But, I wouldn't feel comfortable cutting back the root ball hard, with such a foliage mass.

This brings up an interesting conversation. As you've noted you've had success with using larger grow boxes, ie more of an Anderson Flat style and leaving most foliage intact, in order to push root and trunk growth, Do you leave your root ball just large enough to fit the larger box? or cut it back hard, in order for it to grow into the larger space?

@sorce brought up an interesting point (that works for him), in that, starting with a smaller colander style, encourages feeder roots closer to the trunk, and then split potting continues the feeder roots laterally. In order to do so, initially, one would have to reduce the root ball significantly, and reducing foliage in this case would be smart, due to the reduced energy in the root ball.

They are both interesting methods but like you say which is most specific to my goals for this tree? Which are:

1. Get it out of the ground
2. Increase right hand trunk size
3. Stunt left hand trunk size
4. Encourage compact feeder root system.

I hope I summarized both correctly.

(And I don't mind watering twice a day, if it will give me faster growth. I would also go heavy with my pine bark in the mix, looking for high moisture retention.)

 

[River's Edge]

This brings up an interesting conversation. As you've noted you've had success with using larger grow boxes, ie more of an Anderson Flat style and leaving most foliage intact, in order to push root and trunk growth, Do you leave your root ball just large enough to fit the larger box? or cut it back hard, in order for it to grow into the larger space?

This is based on the stage of development of the root ball once again. I do the most that I can in one session. But this will be different depending on what I find with each particular tree. The destination is usually a couple of stops away.

Leaving the root ball just large enough to allow roots room for some growth is important when collecting yamadori and during the first stage of recovery. ( key thought: often the advice we receive is based on a particular set of circumstances not for general use each time we approach a tree) This may and often should involve a change of sizing in grow boxes or maintenance pots as the tree progresses in developing finer feeder roots.

The tree has a nursery pot developed root ball and was transplanted without root work or disturbing the mass a short time ago. Actually in reality, probably has never had root pruning for development.
As a maple I would carefully bare root, wash out nursery soil. Reduce the strongest roots, particularly the downward ones. Locate the best root spread for nebari. If the root ball was really healthy in appearance I would likely reduce by 2/3 the first go. If I found a less than healthy situation, I would remove all dead roots and keep all healthy roots.
In other words adjust the situation depending on what you find.

I would advise focussing on #1 and #4 first.
When the tree has shown strong signs of recovery after potting. Than begin pruning/ cut back to accomplish the other goals.
If you stage the work the recovery will be faster with better root growth due to the extra foliage and reserves left in the tree. This in turn will give you a stronger tree for better response when cut back.