How hard can you root prune a Crepe Myrtle?

[longd_au]

I have seen some extreme root pruning for trident maples and elms. Does anyone know if the same can be done to Myrtles?
There is a beautiful myrtle growing in the garden for the last 5 years and I think will make a great pre-bonsai. The problem is, when I gave it a push, it seems to be solidly anchored.
It is a dwarf specie, around 1m high with a trunk of around 7-9cm.

The buds have not started moving. I quick dig around the plant didn't expose much surface roots so I am thinking they must be straight down.
What would be the best approach to transforming this tree into a pre-bonsai?

I am thinking to wait for the buds to swell, then dig around 15cm on one side of the tree and cut off any large roots. Also give the top a prune to match.
Then the following season, depending on how it responses, dig the other side of the tree and do the same.

Does this sound like a safe option or can I just do the whole tree in one season?

I am new to bonsai and new to this site. Thanks in advance for all the great articles that I've read. Hopefully, I can contribute to this resource in the near future.

[shibui]

Crepe myrtle is remarkable tough and can handle root reduction well. I would do such a tree in one go - dig, prune roots as hard as necessary and cut the top back then pot up all in 1 go.

[longd_au]

Thanks Shibui.
We have met in August when I came to pay you a visit which was truly enlightening. A short chat with you is like a life time of knowledge.
I know you hard root prune your tridents in mid/late winter. Do you think it is too late to do it to the Myrtle now? I have not seen any buds movement as mentioned, but this does not mean activities have not started below.

[shibui]

No buds means the tree has time to heal and produce more roots before it needs water for new leaves so no buds means OK to prune roots Dennis. I would do it now.

[kcpoole]

My crepe are on starting to Bud this week here, so if I had not already repotted, they could be done now.
Root prune as hard as you like.

Ken