height of the pot for tree health

[Mara of dragon clan]

Hello all, happy spring
I repotted a juniper recently, but I am wondering if the pot I decided on is too shallow for the health of the tree. How do you normally decide how deep a pot should be as it transitions from nursery can? I did a half height root work on the tree last year and this time when i checked the roots the original pot i had planned to use was really large- the only difference between its previous container was that the new 1 could let it grow a more rectangular root base. because it was so large i decided to try potting it to a smaller size, but i remember that there was something said about how much of the soil line is acceptable above the lip of the pot. TIA

my bench tour coming soon. had a bunch of my pots finally joining their tree counter parts this year.

 

[River's Edge]

How do you normally decide how deep a pot should be as it transitions from nursery can?

I base this on the shape and condition of the root ball, keeping in mind the species. So it depends. My basic guideline is to stage the transition rather than force it by some formulae. I prune the downward growing roots to an acceptable limit each time and then place the root ball in an appropriate depth container. Rinse and repeat until I have reached the desired size and depth of root ball in proportion to the tree. A basic guideline to work towards is a depth of pot that is similar to the the width of the trunk at the base just above the nebari. So 3 inch trunk, roughly a 3 inch depth pot.
From a nursery can of 12 inch depth, the first stage could be anywhere from a six inch to 4 inch depth. Wait two years and reduce down to a three or four inch depth. Just an example! if it is a collected Yamadori in a nursery can the stage may be much longer to accomplish. Generally the older the tree the more careful and cautious one should be. Given that some species handle root pruning much better than others allow for variation by species.

 

[Shibui]

Sometimes words alone can be ambiguous and maybe readers don't get the correct message. That's where pictures can help make the message clear.

There is much written about bonsai pots and potting. Not all of it is absolutely correct so I feel free to do whatever looks good and works OK.
I've seen plenty of bonsai potted with the soil mounded up so the roots are well above the rim of the pot but at least one of the Japanese bonsai teachers told us that was not a good way. It certainly makes it harder to keep soil in the pot, keep the roots covered and makes it hard to water properly so probably makes sense to have bonsai potted down lower in the pot though most of mine are not necessarily below the rim of the pots.
Some years ago there was a fad for really shallow pots but we found that shallow pots are detrimental to the trees, especially where summers are hot so I've moved toward slightly deeper pots for my bonsai.
Even now I see occasional posts of growers trying to fit bonsai into the smallest possible pots. Pots should fit the tree, balance the look rather than being the smallest you can fit the roots into.

When transitioning from deeper nursery pots to bonsai trays it depends on the species. Some species can be root pruned really hard and moved from deeper pot to shallow in a single move. Others don't recover as quick so we need to transition slowly and juniper is one of those. Each situation is different so I don't like to make blanket statements about how much and how often.

Sometimes moving to a shallow but wider training pot would be a sensible intermediate step and may be better than trying to put a root ball into a pot that's too small.

 

[FinnLakk]

So 3 inch trunk, roughly a 3 inch depth pot

I've been wondering, the 3" depth of pot, would you interpret that as the interior or exterior depth of the pot?

 

[rockm]

For the tree's health, it is the INSIDE depth that is important. Transitioning from a nursery can to an initial bonsai pot is an intermediate step. Esthetics take a backseat. Health in that transition is the primary objective. The transition has everything to do with what the root mass looks like and how much reduction can be done. There is no easy answer or formula. It depends on the tree. Deciduous species can take more reduction than conifers.

Forcing a tree into the shallowest container possible right out of a nursery pot usually ends badly for the tree...

 

[Shibui]

I've been wondering, the 3" depth of pot, would you interpret that as the interior or exterior depth of the pot?

I've always taken this guideline with a healthy grain of salt so interior or exterior is irrelevant. With this guideline most smaller juniper bonsai would be in pots less than an inch deep. I doubt I could keep a tree alive through summer in such a pot. At what trunk thickness should we start observing the pot depth = trunk thick guideline?
Some of my older bonsai with really good trunk taper and nebari easily exceed trunk thickness to pot height and still look fine and thrive.
To me it is far more about sensible pot sizing taking into account species, appearance and external conditions.

 

[Cajunrider]

Sometimes words alone can be ambiguous and maybe readers don't get the correct message. That's where pictures can help make the message clear.

There is much written about bonsai pots and potting. Not all of it is absolutely correct so I feel free to do whatever looks good and works OK.
I've seen plenty of bonsai potted with the soil mounded up so the roots are well above the rim of the pot but at least one of the Japanese bonsai teachers told us that was not a good way. It certainly makes it harder to keep soil in the pot, keep the roots covered and makes it hard to water properly so probably makes sense to have bonsai potted down lower in the pot though most of mine are not necessarily below the rim of the pots.
Some years ago there was a fad for really shallow pots but we found that shallow pots are detrimental to the trees, especially where summers are hot so I've moved toward slightly deeper pots for my bonsai.
Even now I see occasional posts of growers trying to fit bonsai into the smallest possible pots. Pots should fit the tree, balance the look rather than being the smallest you can fit the roots into.

When transitioning from deeper nursery pots to bonsai trays it depends on the species. Some species can be root pruned really hard and moved from deeper pot to shallow in a single move. Others don't recover as quick so we need to transition slowly and juniper is one of those. Each situation is different so I don't like to make blanket statements about how much and how often.

Sometimes moving to a shallow but wider training pot would be a sensible intermediate step and may be better than trying to put a root ball into a pot that's too small.

Great advice. Where I am it can get very hot in the summer. I am planning for slightly deeper pots and soil that holds moisture a little longer, most particularly with maples. Even with all that, in the summer I have to move my maples under my porch where they only get a few hours of morning sun. Otherwise the leaves get crispy and the trees falter. I am able to keep my maples growing all through the summer that way in Louisiana. The only downside is I have to rotate the pots very often for even growth.

 

[Mara of dragon clan]

If a bit of the root mass is above soil level but covered in moss will it be ok? also i went from 6 inch to 2 inch this year. is it a disservice to the tree if i repot it to a 4 inch? i repotted it just last thursday, but the roots had been worked on already to fit it to the 2 inch pot

 

[RKatzin]

I have never hurt a tree by going a little oversize on the pots. I have however killed many trees shoehorning them into a pot that was to small.
I think it's early enough still to give the tree a potting up.

 

[Mara of dragon clan]

I have never hurt a tree by going a little oversize on the pots. I have however killed many trees shoehorning them into a pot that was to small.
I think it's early enough still to give the tree a potting up.

many thanks!

 

[Shibui]

If a bit of the root mass is above soil level but covered in moss will it be ok? also i went from 6 inch to 2 inch this year. is it a disservice to the tree if i repot it to a 4 inch? i repotted it just last thursday, but the roots had been worked on already to fit it to the 2 inch pot

Still no pics so again, difficult to give specific advice.
Root mass above the rim of the pot is not a problem in itself. The problem comes if soil washes away while watering all through the coming year. The problem comes if you cannot water effectively because all the water runs off before soaking into the soil. So much depends on the type of soil, how high the roots are, whether you have experience watering small pots, whether to pot is full of roots or has plenty of new soil, etc, etc, etc.

Depth of pots is not the only dimension. Volume has a big bearing on how well a tree grows too so 6' to 2' to 4' deep really tells us nothing.

Plants repotted in the last week can safely be changed. Problems can come when the roots have started to regrow but rarely so soon after repot.

You know how much experience you have. You know how confident you are at watering trees in small pots. You know how much risk you are willing to take with this tree. We can only guess at these factors and therefore cannot make decisions on your behalf, only put forward possibilities and likelihood.
Guessing from the tone of these pots that you are inexperienced and don't want to take risks and knowing that keeping trees alive in small pots is difficult I would advise repot into the larger 4' pot for this summer to get more experience while having a larger safety margin for watering and tree health.

One of the hardest but best lessons in bonsai is to take time. Bonsai is about years of development. It does not all have to be done this year.