ROR substrate question

[bonsailevel:master]

I'm going to be doing my first root over rock this coming spring. I'll be using an Acer Rubrum that I collected last spring. My question is this,... can I use a different substrate on the same "level " as the rock/wrapped roots? I don't see any need to use a lot of bonsai soil where i don't want roots anyway. I make my own soil so it is a time consuming job. Didn't know if regular potting soil or something similar would suffice. Any thoughts or input on what others would do or have done are much appreciated.

 

[Wires_Guy_wires]

I try to use a coarse mix around the rock so that the roots try to dig down deep and fatten up rather quick. Below the rock I use regular potting soil with a bunch of perlite.

Bonsaify on youtube has a video on repotting black pine seedlings, and a bunch of them in very coarse perlite made seriously thick roots. I started my ROR's before that video existed, but it's a nice example of what can happen.

If anything, I'd put the dirt on the bottom instead of the top. It will flush down anyways. The roots will find the dirt and produce a mat of fine roots there, instead of around your rock.
Some sphagnum around the upper roots might be a good idea though, especially if they're still young.

 

[James W.]

I'm going to be doing my first root over rock this coming spring. I'll be using an Acer Rubrum that I collected last spring. My question is this,... can I use a different substrate on the same "level " as the rock/wrapped roots? I don't see any need to use a lot of bonsai soil where i don't want roots anyway. I make my own soil so it is a time consuming job. Didn't know if regular potting soil or something similar would suffice. Any thoughts or input on what others would do or have done are much appreciated.

Where you have "different substrate?" I use mulch, usually shredded cypress but whatever is cheap.

 

[Shibui]

Maples are notorious for growing new roots at surface level. Once a surface root gets going the deeper roots seem to stop growing. That's the reason I developed foil wrap for ROR maples.
You are free to try any methods you wish but I don't think different soil on different levels will make a lot of difference to how the tree grows.
At some stage you will want accelerated growth to thicken the trunk. Half a box of soil won't do anything to speed up growth.

 

[Kievnstavick]

In a very basic sense, using any sort of soil or substrate will lead to roots in that area. I'd advise against putting potting soil on top as it will probably lead to fine feeder roots up there and also make it harder to gauge if you are watering correctly. Fine substrate or potting soil on the bottom would work out much better as it will hold water for longer (and be in the water column) which the roots will be seeking out.

If you are really concerned with rootd growing out rather then down the rock, I would consider limiting the amount of growing area it has out side of the rock. Using a wrap (tube, box, etc) filled with a substrate (preferably something the dries out faster then your pot-level substrate) like Shibui meantion is a decent way to go about it.

 

[Srt8madness]

Shibui's foil method is tried and true. A search will show his thread detailing the process step by step, and the results he has achieved.