Trunk Thickening in Pots

[one_bonsai]

When growing plants in large pots to thicken the trunk, is it best to use potting mix or bonsai mix?

[Ryceman3]

Use whatever mix your comfortable with. I like to keep the mix I use consistent because I have a good idea of when to water and how often for one thing, and I don't need to remember which plants are in what type of mix... every tree is the same! But if you are comfortable with potting mix as a medium to grow on your trees, I think it will be fine ... the tree probably won't know.

[Shills]

I believe that soil type is not a huge issue at the trunk-growing stage. This is because you are presumably using a nice big pot with plenty of room for roots to spread and grow. Having a tree with a large root system means your tree is less vulnerable to upsets down there (root rot or wet feet, drying, lack of oxygen etc). The main reason bonsai wisdom advises the use of loose 'bonsai mix' is because the limited root system of a bonsai is so vulnerable,in that tiny pot. Having loose soil reduces the risk of suffocation and wet feet (you just gotta keep it watered and fed).

I think at the trunk-growing stage any soil will do once the tree is established. Just remember to put a plate or flat implement just beneath the root ball to encourage the roots to grow horizontal and hopefully increase the nebari.

However I am not an expert and curious what others think...

[Beano]

I thought there was some merit to the idea/research that larger particle size in potting mix is best for rapid growth ie trunk thickening and when trunk is developed and you want to work on ramification and leaf reduction, a finer mix is called for? I remember Treeman talking about this before, maybe he’ll weigh in.

[shibui]

An ad once stated that 'oils ain't oils' and the same applies to bonsai mix. Each brand is different. Even more troubling is that the same brand can be quite variable from year to year and batch to batch. Some members of our club found the best mix for bonsai was actually 'cacti and succulent' mix.
In reality, bonsai mix is really just a potting mix. Sure we like to believe it has some extra special properties but the reality is that any potting mix with larger particles and good drainage works really well for bonsai. You can also learn to grow good bonsai in almost any potting mix so it is not important whether you use a good potting mix or 'bonsai' mix.

As Shills has said, the larger the pot the less critical the quality of the mix so in larger grow pots you can use whatever you like. Just remember that potting mix is much like so many other aspects of life - you get what you pay for, so don't expect premium growth from a budget potting mix. Feeding and matching watering to the mix, pot size, location and state of growth are all important factors.

[one_bonsai]

What about the fact that if grown in potting mix you'll have get rid of the potting mix from the roots at some point possibly killing the plant. Where as if grown in bonsai mix you don't really have this problem

[Max]

you will be removing roots, raking out roots, trimming roots for years to come. Potting mix deteriorates over time plus your trunk growing, after that into a training box for a few more years, you can use the same potting mix brand if your happy with it, sifted of the larger stuff with sand added, because this is when your after finer feeding roots

[shibui]

you'll have get rid of the potting mix from the roots at some point possibly killing the plant.

Who said that removing soil/mix from the roots will (possibly) kill a tree? I have found this to be almost complete fallacy. I routinely bare root pines, junipers, maples, almost any species and have rarely seen death as a result.
max is absolutely correct to point out that we regularly need to rake old mix out of the inner root ball as it deteriorates. Sludgy, broken down mix and field soil kills far more bonsai than bare rooting does

Also take into account that many potting mixes are as good, sometimes better, than 'bonsai mix' as I tried to point out above. Why would you rake out good mix just to replace with other good mix? I grow a lot of plants here. They all grow in the same mix- seedlings, grow pots, maples, pines, azaleas, older trees, bonsai pots. Everything is in the same mix and it seems to work OK for me.
Beginners especially seem to look for possible problems when there are none.

[Pat3222]

I agree - potting mix works for me in this scenario. Neil makes some great points on varied quality and getting what you pay for. I prefer to buy a cheap mix as it has no fertiliser (the $3 Bunnings stuff is generally pretty chunky) then tailor that to what I’m potting by adding as needed fertilisers, course grit, blood and bone, pelletised chicken manure or even a handful of straight manure and garden compost to the swamp Cypress which are belting along since.
Cheers

[one_bonsai]

Who said that removing soil/mix from the roots will (possibly) kill a tree? I have found this to be almost complete fallacy.

I just keep hearing not to bare-root Junipers.

[Ryceman3]

Who said that removing soil/mix from the roots will (possibly) kill a tree? I have found this to be almost complete fallacy.

I just keep hearing not to bare-root Junipers.

Yeah... you can

[Max]

bare root, wash, rake, wash, root prune, wash, examine, wash. I think that never (never) letting roots dry is the key, how log can you hold your breathe, think as your tree, be your tree, understand your tree, push beyond maybe once, maybe thrice, but it will weaken. Then what? experiment by all means, but not something that has not been done and dusted (new strain?) that would waste valuable growing time, i enjoy watching my sticks - change - thicken - pest attack - flower/die - dry out _hopefully survive i think learning is the joy remember, you may pass on, but your tree, the one you grew from seed.

Humble

[kb bonsai]

I am with Shills and Neil on this one. Having recently (3 yrs) relocated from the mainland to Tas, and starting my collection again, all my plants are in the "trunk fattening" phase.
I purchase a "premium" potting mix and add varying amounts of grit ( seived, 2 - 6mm but not too fussy so long as the fines are out) depending on the species.
No grit added for Fuchsia / Azalea thru to 50/50 for pines , slightly less for Junipers.
When I acquire a new tree , (and usually they are the neglected / pot bound ones that I hunt around the back of the nurseries for) regardless of the species they all get the same treatment. Out of the pot and bare rooted if required to be root pruned back to a "reasonable' set of roots. Then re potted into grow pots , maybe some seasol , kept in the shade house untill I see some growth response. My logic is that if I can't get the plant back to acceptable roots to begin then it has no future as a bonsai.
At this point my mortality rate is extremely low. I have had several sulk for some months before they show some growth but rare.
Some plants have now been transferred to bonsai training pots, at this stage I just rake out the roots as much as required to trim to fit pot and use a coarse scoria / Diatomite / grit / potting mix mixture blend suitable once again for the species.

At this point in time I believe I am getting very good growth rates and no major issues with this methodology.

Just my 10 cents worth , KB

[shibui]

I just keep hearing not to bare-root Junipers.

Have you never heard things that you knew or since found out to be incorrect? I've been around long enough to know that many things people say are less than absolutely true.

I have washed the roots of maples but would not go that far with conifers. Many have helpful fungi on the roots that help them convert food. Washing might just get rid of the good guys a bit too much. In normally cut rots back a bit them shake loose soil/mix off. If there's lots of really tough clay or soil I'll rake most out. Leaving a little does not seem to hurt but try to get rid of most field soil and most decomposed potting mix when transplanting. Good potting mix can be left in situ.

I know there are lots of others who have different ways of doing it. Most ways seem to work reasonably well but I think some methods need particular care regime to make it work well. Sometimes those people don't even know they are doing anything different or special to match their methods.
You can follow whatever methods you wish and will probably have success. Just don't then go telling others that your method is the only one that works.

[Tambrand]

I found -

[1] our local Willow leaf ficus can trunk thicken in a 2.5 cm deep bonsai shaped
pot. Just grow a branch extension of around 1 m.

[2] Yet in the same family the Chlorophora t [ Fustic ] with the same branch extension
will only thicken the branch.
The tree needs to grow the top for trunk expansion.

[3] The J.B.pine does well in a 30 cm x less than 15 cm porous clay pot, with
1 m extensions. soil is gravel and 1/3 aged compost.

[4] Elm root cuttings work well in the 1/3 55 US gallon black barrels.

[5] The house here came with growing troughs for ornamental plants - gerbera for
example.
So I trunk thicken in a rectangular shape that is about 3 m long by 35 cm wide and
about 38 cm deep.
Soil was a clay type loam [ called Top Soil on my side ] added in gravel for
better drainage.
\
My soil in pots is 5 mm silica based gravel, if needed 1/3 5 mm crushed red building
brick [ block ] it is porous.
With no more than 1/3 aged compost [ holds 20 times it's weight in water /fertiliser ]
Aged means held justmoist in a barrel so weed seeds can germinate in a covered barrel
and die.

I did a 30 year check on my trees and the soil mix discourages thick roots. Encourages
fine feeder roots.
This is my 40th year growing trees as bonsai.
No insect problems just 2 pests, Using Rodales information - Organic growing.

Doing an experiment presently, studying the Fustic. 2 years ago.
6 months to get an 8 cm trunk - tree to 244 cm height.

2nd plant.
Last year - cut trunk to observe healing time and effect on trink thickening.

This plant is a found sapling that has similar branching to a Zelkova and elm
type leaves and I am using cuttings to experiment on.
Laters,
Tambrand

*I have no need to bare root and using the pie cut system over time I can
change all of the soil if needed.