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 soil?

 

[Adair M]

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

Modified bonsai soil.

The problem with potting mix is it usually keeps tree roots too wet. It’s designed for annuals. Non woody plants.

To get trunk thickening, you want lots of root growth, so a good way is to use an oversized wooden box. Which will be expensive to fill with bonsai mix. So, use a large proportion of pumice. Roots grow fast in it, and it’s relatively cheap.

 

[Tieball]

I’m growing some trees in the ground and some in wooden boxes. In wooden boxes I use a bonsai mix with some added aged pine bark. The trees do thicken....however, not as fast as if they were in the ground growing in native or modified soil. But, that being said, yes...I’m happy with the box growing results. I generally grow the trees in the ground first...fatten up...drastically root prune (very drastically)...prune off a lot of branches...then put them in boxes wired down securely...and let them grow a couple seasons before root pruning again. They do thicken growing in the boxes....perhaps slowly, but they do thicken. More like controlled growth.

American Elms, Zelkova and Hackberry trees that I have respond well to this treatment. I do prefer the wooden boxes. What container is used may not make a difference. My winters are harsh and the trees are outdoors all year though. The wood provides a strong stability for growing and creates some cold weather insulation...and is easy to move around. The substrate makes the different to me. No potting soil...that turns into mud with no air circulation.

My wood boxes are all the same size. This makes it easy to cluster them together during the winter. And it’s a good size for me to lift.

Do you have particular tree species you’re planning on growing this way? That information may help slant reader’s suggestions in the right direction. Just a thought.

 

[one_bonsai]

Do you have particular tree species you’re planning on growing this way?

Juniper

 

[Tieball]

Oh. Hopefully your question catches the eye of someone with Juniper experience. I really don’t have any Junipers....just deciduous trees. That being said....I’m confident that potting soil is not a good solution. Someone with Juniper experience may share their special blend and characteristics of a mix.

 

[KiwiPlantGuy]

Juniper

Hi, I am having success using grow boxes for my juniper starting material. My mix (vaguely cheap ) is 30% of each pumice, perlite, and pine bark. If that helps any.
Charles

 

[ThirdCoastBorn]

Jumping in as a fellow beginner, it's amusing in hindsight to see the various substrate mixes I tried over the past 3 months as my knowledge of soil mechanics increased slowly but surely, while keeping an eye on budget. I've got the bug this past summer and have a lot of trees (not all necessarily with an eye for bonsai) growing out, so can't afford to sink everything immediately into 1/3 lava, pumice, akadama.

More recently, I've settled on the mix(es) described by Brent Walston of EvergreenGardenWorks: http://www.evergreengardenworks.com/soils.htm 8:8:1 Pine Bark, Perlite/Pumice, Peat. I got 10 bareroot saplings a few weeks ago that are still dormant in it, but have been pleased with the way it dries. Yesterday, I put 48 seedlings into Rootmakers using a more dense mix of 4:4:1, but can't tell yet how well that works. Would have preferred to use pumice, but is currently backordered from my store's distributor so settled for the perlite. For the pine bark, a local landscaping supply mixes their own potting soil for cheap and I use the sifted pieces > 1/8" -- haven't found a good source for raw pine bark of the right size but hopefully will in the next month!