Years ago an acquaintance gifted with me with a strange tree he had "created".
Basically he had a nice rock with a hole going from side to side. And a young fig spontaneously growing in the garden.
He cut the fig back and put the rock on it so that the trunk went through the hole.

A couple of years later he moved it to a pot and gave it to me, as he had no idea on what to do with it.

I've been shaping it somehow for the last few years, and it is a bit of a pain (obviously) both for repotting and watering, as the rock at its base covers most of the pot, making things complicated. Still, I like it.

Now the trunk has finally grown large enough to completely fill the hole and what I'd like to do next is force it to grow new roots above the rock, where the trunk comes out of the hole, slowly moving it into something a bit easier to maintain while adding more features to its already settled character.

What's the best way to obtain that, tho?

What I'd do is -at the very beginning of the next growing season- remove some bark where I want the new roots to grow, put some rooting hormone on it and cover with some wet sphagnum; then bury the rock entirely, covering with a couple of cm of soil the treated part.

Would I be doing it right?
And would you suggest to do it with or without trimming some the existing roots (the idea being soliciting the plant to grow more roots)?
Other suggestions?

Thanks in advance.

When I read your question I immediately thought "ground layering".
The point is if the "usual" ground layering system of making a thick wire girdle around the lower trunk to force the roots to grow above the wire will probably result in a weird root over rock style (if it work at all).
Perhaps the hole in the rock itself will substitute the wire's work and choke the trunk into making the new roots if you bury the whole set.
Could you please show us a picture to make it more obvious?

Clicio wrote:

When I read your question I immediately thought "ground layering".
The point is if the "usual" ground layering system of making a thick wire girdle around the lower trunk to force the roots to grow above the wire will probably result in a weird root over rock style (if it work at all).
Perhaps the hole in the rock itself will substitute the wire's work and choke the trunk into making the new roots if you bury the whole set.
Could you please show us a picture to make it more obvious?

That was indeed my same thought. With a caveat, tho: I'd like to "guide" the roots to go towards specific directions if possible, as the rock has other smaller holes that I'd like to use to let roots go through.
So, if there's a way, I'd like to be able to "decide" where roots would grow.

I'll send a picture as soon as I'm home, tho, to make it a bit clearer (currently sitting in an airport...)

Ok, here are some pictures.

First one from the side, so you get an overall idea of the tree.


Here is a close-up of where the trunk enters the rock.


Right on the right side of the trunk is one of the "other holes" i was referring to: its exit point is that other hole farther on the right, with all that moss:



I won't add other images, but there are a couple of similar (but smaller) holes on the opposite side of the rock. I would like new roots to go through there.
The decision is then if I should just let new roots grow by simply burying the lower part of the trunk with the entire stone, as in a "natural tourniquet", to then select the ones I want to keep, or id there's a way to "guide" the tree to grow roots in the place I'd like 'em...

Back to this one after 1+ year, for an update.

I did exactly what Clicio suggested: buried the plant with the entire rock for a season. Used pure pumice and made sure to give it a lot of water throughout the entire season; for the rest, fertilized as usual.




Yesterday I took it out of the pot to check how it was going and do some rootwork. Yes, wrong time of the year and all, but I like to think I know what I can do to this plant by now, so bear with me.

The root growth has been massive. To the point my fist question after lifting the plant had been "Ok, now how the hell do I make the rock visible again?!?"




"With chopsticks and a lot of patience" is the obvious answer. Turned out that, maybe as expected, there was no reason to try pushing roots through the holes I wanted them to go into: some found their way through them on their own.




In order to try getting a bit of control on roots placement and growth direction, I looped some loose aluminium wire around groups of roots, and used some larger gauge wire around a couple of stiffer ones to try placing them where I wanted them to go.




Then everything went back underground and it will stay there for another growing season before I take another look at it.
Didn't do any work on the aerial part for now, I'll wait spring for that.

I have no idea if what I'm doing makes entirely sense, as this is the first time I attempt something like this; but as long as the plant won't suffer from it, it'll be useful experience anyway...

Good to see this healthy.
No take it back out of the pot and remote the wires.

Did you see the size of the roots that grew this year? What do you think will happen when there is a wire: You will get loads of scars on the roots which will not easily disappear.

Consider using e.g. alu foil or cotton (!) twine to put it in place. Once the pot is filled with substrate the roots will not move around anymore, and cotton will rot away soon.

If you use alu foil you effectively separate the roots from the rest of the substrate: In the end you want the roots to grow at the bottom of the rock, and not away in all directions.

Just some thoughts from my side. Oh, and I have repotted most of my trees already. Only some more sensitive species (trident, olives, wisteria) have to wait till spring.

BofhSkull wrote:

I did exactly what Clicio suggested: buried the plant with the entire rock for a season.
I looped some loose aluminium wire around groups of roots, and used some larger gauge wire around a couple of stiffer ones to try placing them where I wanted them to go.

I am very glad it turned out so successful, congrats!
But I have to agree with LB, I would have used cotton or sisal or jute to direct the roots, not wires.
Can you imagine a "roots over rock" beauty with all roots... Damaged?
Not pretty.