When is a pot too big?

[Joe Dupre']

I went to a budding bonsai friend's house today to check out his collection. He has been doing his homework! Perhaps 30 different species of trees which seemed to all be in good health. Nothing very big, but pretty nicely kept for having been in the hobby for just a year. His junipers struck me as being lush and green. That's the conundrum. He had a couple in homemade cedar board boxes that were about 12" x 12" x 5" deep. The soil seemed to be a good-draining mix. The junipers were in the neighborhood of index finger to thumb sized. I praised him for all of his good work but questioned his use of such a big container for the junipers. He assured me that the trees use the moisture up in 1 to 2 days. I don't have a ton of experience with junipers, so how big is too big..............for junipers and even deciduous trees?

 

[nuttiest]

I wonder if well drained soil = no limit. It seems that way with pure pumice.

 

[sorce]

Seems with the coarse soil most people use, there isn't much "water table" to speak of.

Depends on the soil.

Sorce

 

[nuttiest]

I think the roots would limit themselves, and blow over in wind.

 

[LittleDingus]

I feel the only dimension that can be too big is depth. I try to keep between 5-7" depth these days.

Width is only a matter of practicality. How much space do you have vs how important a nebari is to you.

Yes, there is truth to bigger soil volumes maintaining more moisture...but there are limits. For a given depth, surface area goes up faster than perimeter. Once you get to larger sizes, evaporation from the surface can start to have significant effect on moisture levels down to a few inches. My trees in wider pots need MORE frequent watering than the smaller pots.

Then there's the nebari to consider. Our intuition tends to trick us into thinking trees grow different than they do. That branch at 6" off the soil will still be at 6" off the soil after the tree doubles in size. It will not stretch up to 12". Except at the extension points, new growth consumes old growth...it doesn't lengthen it.

IMO, if you want a 6" nebari at the end of the day, you need to start with a 12" or wider pot! The tree may fit in a 6" pot but once the roots hit the walls, they turn...and now they no longer have the room to flare as we might expect. You also get a lot more crossing roots in smaller pots as the tree buds back new roots attempting to draw in more resources to power growth. Newly budded roots can't grow through existing roots so they grow around them...

As far as wind, I have trees that tip over even in 20"+ pots (well, bags...I use grow bags). If the canopies do not interfere, I will pack them next to each other for support. Or I just stand them back up every time I pass them. The problem with tipping, though, is that it reorients gravity and affects the water column. You can get an asymmetric nebari if the tree spends too much time on its side. Young growth will also bend up and towards the light.

The deer pruned off all the low growth on a slippery elm that was a yard volunteer a few years ago. Because of that, I decided to put it in a bonsai pot before its time



The tree was in a 5 gallon grow bag filled to 5" deep. The tree was about 5' tall. The trunk was laser beam straight up in relation to the soil. But it's obvious which side it rested on when it tipped over!

 

[dbonsaiw]

Interesting to hear about things tipping over in such large pots. I have a number of trees growing in large grow boxes and short of a earthquake there's no way its tipping over.

 

[nuttiest]

lol i meant the tree itself

 

[penumbra]

It has a lot more to do with the substrate than it does the pot size.

 

[nuttiest]

It has a lot more to do with the substrate than it does the pot size.

Exactly. And oxygen. Too much oxygen and nutrients... roots have no reason to search. Pumice brillo pad.

 

[rockm]

Actually, soil volume and soil composition are hand-in-glove as reasons overpotting is mostly bad.

"The reason the plant is showing signs of stress is because the large volume of new compost that was added when it was potted up is sitting wet for a long period, reducing aeration around the roots. Instead of the roots growing out into the new compost, they simply rot.

Although the compost will dry naturally through evaporation, it takes longer when there is a greater proportion of compost to roots. The more fresh compost there is, the more it will stay wet, creating a soggy ring around the rootball. Finer growing medias that hold onto more water are particularly prone."

Overpotting / RHS Gardening

Plants in pots need potting up every year or two to allow more space for their roots to develop and to replace tired compost. But getting the right sized pot is important for success and when the pot is too large problems with overpotting can arise.

www.rhs.org.uk

 

[dbonsaiw]

FWIW, I have not yet had any issues growing trees in 40% pumice, 40% calcined clay and 20% pine bark in 14X14X5" grow boxes (other than cost). Roots seem to do a decent job at colonizing the soil before there is an issue in any event.

I also have yet to see a tree refuse to cross a different substrate. I think Ryan Neil actually encourages leaving potting soil in the root ball at repot. I've had trees grow roots fine from pure sphagnum moss to bonsai soil when I first remove my layers, and from potting soil to bonsai soil if I don't totally bare root a new tree.

I also have never had roots too pampered to run. I tend to fertilize on the heavy side and the roots grow nevertheless. My limited observation is that roots do what roots do if given the space to do it. Doesn't the P-K encourage the roots to grow?

(All deciduous trees btw).

 

[rockm]

i have seen trees fail to grow in oversized containers. I've had to save several boxwood that were planted in oversized grow boxes and swamped with soil.

I've seen roots circle in like soil and not cross into different soil types.

 

[dbonsaiw]

i have seen trees fail to grow in oversized containers. I've had to save several boxwood that were planted in oversized grow boxes and swamped with soil.

I've seen roots circle in like soil and not cross into different soil types.

My experience is very limited, both temporally (I'm only at this a few years) and in respect of the trees I work with (really only deciduous). The advise you shared is clearly sound and in fact what many with your experience would likely say. I was only sharing my limited anecdotal experience. Not sure if this makes a difference, but I have never simply pulled a tree from one pot and placed it another pot with differing substrate. Rather, for example, I have cut half the soil/roots off a nursery tree, combed out the top etc. and then placed it in a different substrate.

 

[BobbyLane]

@clem seems to be having great results with oversized, but fairly shallow grow boxes. Ive never used large wooden boxes before but plan to have a couple trees in them shortly. Which is one reason why ive opted for a slightly less moisture retentive mix this season, since its easy to keep trees too wet in large boxes. Im past the stage of watering trees for the sake of it now though, trees can go days at a time without watering in larger boxes with moisture retentive soil. In my early years im not sure id have been able to restrain myself...
Your watering habits will be key.

 

[BobbyLane]

This season I have 2-3 trees in oversized pots, that appear to be somewhat drowning the tree, but looks are decieving. They've came out of nursery containers and the main roots have been left long, much longer than is needed for bonsai, and the roots are actually near the edges of these oversized pots, ive left many of the courser, thicker roots intact, this is because im still looking to increase trunk girth. The trees already have decent nebari and the roots can be cut back hard for bonsai at another time. Its often recommended to get the roots right first, but I dont think its always that important, maybe more important for the trees that have really terrible or non existent roots/nebari.

 

[Joe Dupre']

I guess, like in everything, it depends. The responses gave me a lot to chew on. Anecdotal experiences, while maybe not the final word, do give some parameters to work from. My experience leads me to wager that a tree with a vigorous root system already present probably could go into a new container that holds twice as much soil. Newly collected trees with marginal root systems probably should go into a lot smaller container.

 

[leatherback]

Pots get too big when roots cannot such the water out, and create air pockets after watering. Open coarse bonsai substrate has airpockets by itself. Finer bonsai soil does create saturated conditions after watering where a tree can really suffer.

 

[Cajunrider]

All the things that have been mentioned about over-potting are correct.
The only exception I have found is bald cypress. Nowadays I put them in shallow and very wide pots. Much better root flare that way for BCs.