Root over rock Ficus natalensis--hope I did this right!

[SharonP]

I got an F. natalensis from Wigert's recently. After letting it settle in, I wanted to repot and decided to try root-over-rock for the first time. However, I found online instructions confusing. People were talking about wrapping the roots and rock with film wrap or aluminum foil, in which case how would the roots get any water? And I knew there was some step where you bury the whole thing for a year or more. So I just kind of winged it last night.

This was sooo hard. I needed about 6 hands, but only had 1 hand available most of the time because of having to swat all the mosquitoes with my other hand. I had to manhandle the poor tree so much that I accidentally broke off several baby aerial roots along the way, but the tree will hopefully survive.

Here's the before picture with the rock:




Here are photos of the untangled roots before and after washing and pruning:




Here's after tying the roots to the rock with 100% cotton string. From this angle, the roots look well behaved:



From the other side, one large root (on left of photo) wouldn't lie down flat. I didn't want to break it, so I left it as is:



Then I buried the rock and roots completely under the soil using a plastic pot and new soil mix:



I think I now need to leave it undisturbed for a year, but I'm not sure what to do at that point.

Do I just repot it with rock on top, and only rebury the roots that extend below the rock? Or do I uncover the rock gradually, removing the top 1 cm of soil every month until the rock and roots are exposed?

Also, all the root-on-rock trees I see are just a few very thick roots wrapped around the rock. But my tree has a few thick roots and dozens of tiny hair-size roots wrapped on the rock. What happens to those smaller roots once I expose the rock? Do they die back on their own (without damaging the tree)? Do I cut them back, leaving only the thick roots? Was I supposed to remove those thinner roots BEFORE burying the rock?

 

[jason biggs]

don't worry too much - it looks great as is... just leave it alone and let it grow for a full season or 2...
if you live in a warm climate, this tree will explode

 

[gooeytek]

I thinnk that will be fine. @Shibui uses the foil wrap technique and his results have been great. Only requires 2 hands

 

[BrianBay9]

After a year or so, you want to start gradually exposing more and more of the top of the rock. Might take two or three years to get it where you want it. You're probably not going to use those large roots, unless you get lucky. They are less flexible, and less likely to grip the rock. But with a Ficus, maybe I'm wrong. Anyway, as you expose more rock, edit the roots, keeping only those you like that are tight against the rock.

 

[Shibui]

I leave ROR buried until the roots have thickened enough and have a good hold of the rock. After that the whole rock can be exposed in one go. Provided the root tips are still in the soil below they do not are if the soil is reduced gradually or all at once.

Fortunately ficus roots seem to stay put so this should work out even though it has not been wrapped. Try that with a trident maples and you'll find lots of new roots heading off into the soil at the expense of those you have carefully arranged on the rock. That's where the wrap comes in. It keeps the roots growing close to the rock where you want them. Plastic wrap is OK provided your rock is roundish. Foil is better for irregular rocks because it can be moulded to follow all the contours and hold roots even in cracks and hollows. Wrap is around the rock. Top is open so the trunk sticks out and therefore water can get into the roots. Bottom is open so roots can grow out which also lets water out. Works a treat even if you don't want to believe it.

I had to manhandle the poor tree so much that I accidentally broke off several baby aerial roots along the way, but the tree will hopefully survive.

Also fortunately you have chosen a ficus for your first try. They are very resilient and I have no doubt this will just keep growing.

But my tree has a few thick roots and dozens of tiny hair-size roots wrapped on the rock. What happens to those smaller roots once I expose the rock? Do they die back on their own (without damaging the tree)? Do I cut them back, leaving only the thick roots? Was I supposed to remove those thinner roots BEFORE burying the rock?

Those thin roots will probably grow thicker while they are buried. Chances are you'll have lots of thicker roots by next year and possibly a whole lot more smaller ones that have developed.
When you expose the rock any roots that do not have the ends in soil will usually die. I guess that's why some prefer to uncover slowly so those roots are encouraged to grow further down into the soil below.
however too many roots can be a mistake. Remember that each root will thicken along with the trunk. When every root is double current thickness what will it look like? When they are all 4 times thicker what then? My first ROR was also a ficus. After 10 years the roots had all thickened so much they entirely covered the rock and fused together so I no longer had a root over rock, just a huge fat trunk. I now limit the number and placement of roots so that will not happen quickly. I don't think you need worry this year but I would uncover next summer and check what's happening. You can make any adjustments then if required.

 

[SharonP]

Wow, thanks so much for the very useful responses! When gooeytek mentioned @Shibui, I found his website and read all the blog posts on root-over-rock topics. (Example: https://shibuibonsai.com.au/?p=1807).

So yesterday, the day after my initial post, I dug out and undid everything I had done in the photos above. I then cut off the larger roots (which would never conform to the rock) and rewashed everything.



I mounted the tree on a much larger rock that was easier for it to balance on, and will be a lot more visible once the roots fill in than the smaller stone would have been.





I then used a single piece of cotton string + a few strips of aluminum foil to hold everything together. The foil is open on top and bottom to allow for watering and drainage.



After putting the tree + rock + foil into a new/bigger pot I filled it with soil, I finished by making the tree immobile using a guy wire.



When I woke up today, I saw that @Shibui himself had written and basically said the original way I had done it would probably have worked. But I'm glad I did the foil method, because I could see how successful that has been in his blog posts and might as well learn to do it using the "best practices." Now to wait a year to see if it worked!

Thanks again to everybody for the help!