I have a Japanese Acer tree in a pot. The roots have grown through the bottom of the pot and into the ground. I don't think they can have gone deep as under the pot is gravel and then weed control fabric I think I need to repot the tree but don't want to risk killing it as I really like it. Can you tell me the best way to go about separating it from the ground and then reporting it? If I have to break the pot it's not a problem. Thank you.
This often happens with potted plants stood on anything other than a hard surface such as paving, I'm afraid. It's hard to estimate how far down the roots may have penetrated the ground beneath, though the size of the plant in comparison to its pot can be a useful guide.
There is, though, no choice but to remove or break the roots which have gone out of the pot - you can try digging around to see if you can loosen and extract as much root material as possible, but usually, its not possible to get it all because its difficult to move the pot out of the way to gain proper access, and they will have to be cut off.
If the root coming out of the pot is thick, then you may need to break the pot, but if they're just fibrous, it might be possible to extract the plant, leaving the pot intact, otherwise, cut it off. Have ready a larger pot with drainage holes and some fresh potting soil - if the rootball of the Acer, once unpotted, is very dry, soak it in a bucket of water for an hour or so, then transfer to the new pot, packing in new potting soil beneath and around it. Water in well, allowing excess to drain away freely from the bottom of the pot. And this time, stand the pot on something to keep it off the surface below (pot feet or bits of broken tile, whatever); this will prevent the same thing happening again.
Keep well watered - if the top starts to die back because of the loss of root material, you may need to cut down the Acer by up to a third to reduce the strain on it of trying to keep its leaves alive. Alternatively, wait until Fall and do it then, when the plant is no longer supporting foliage and growth in the upper parts.