Hello, I have a question: I have 13y old Maple Palmatum Aureum potted in bonsai pot and I would like to put it in a root pouch and put it in the ground for better growing and thicker trunk.
Can you tell me please when is the best time to do this?
I live in central Europe Czechia so even during April temperatures can go under 0°C occasionally. I can make the repotting process in early March, put the maple in the root pouch a let it indoor in garage or somewhere.. and then put it in the ground when temperatures will be above 10-15°C constantly in later April.
Is this a good idea or do you reccomend better procedure? Maybe the maple can survive this whole process in early March but idk.
Thank you a lot!

It is a hardy species and does not need to be protected. You could once the leaves have dropped put it in the ground, don't touch the roots just make a hole big enough to take the root ball.

thanx  i would prefer to prune the roots before I put it in the ground or root bag.. so I will know the roots are in correct shape and legth

Root work must be done in late winter to early spring. Planting in the ground can be done at any time (except when soil is frozen).

Root pruning and planting in the ground then naturally is best to do as soon as the ground has thawn in spring.

Perfect! Thats exactly what I needed to know 
At the beginning of March at the latest, I will prune the roots and put the maple in a root bag.. and then, depending on the temperatures, I will put it in the ground or wait for more favorable conditions.
Thank you a lot!