If outdoors it will rot eventually even if you do line it. If it is treated pine or fir (seems likely for a cheap container) or cedar or cypress (better, slightly more expensive material choices) it could last 3 - 5 years, even if you don't line it. Personally, I wouldn't line it, taking advantage of wood's porous nature to wick water out.

Or it could be made of white oak or ipe or teak (doubtful) it'd likely last quite a few years (10+) without rotting with or without a liner.

Thanks. Do you think a japanese maple would be ok in it without being lined with plastic.

I don't see why not, but I'm not good at keeping containerized japanese maples alive through winter myself, (zone 7a) no matter what kind of container they are in. I have one that has lived for 4 years and have had 4 others (all repotted in spring when acquired) that died their first winter. Even when in fancy "frost proof" fiberglass containers. Pretty much done trying I have very limited space anyway. The one that lives is in a very average glazed ceramic container, go figure.

If anything, I think a plastic liner has a high potential to impede drainage, which would be particularly detrimental to your japanese maple. Either way I'd also probably drill more holes in the bottom, because its easy to drill wood and they can only help.

I have had a cypress in an 18 inch square cedar container for 4 years without any liner, tree is doing well and the container is on it's last legs, i will replace it in spring and it might start to disintegrate this winter - i'll be wrapping it up tightly just in case.

Hi You can coat it with wood preservative particularly on the inside Polyurethane will double the life . Of course it will stop transpiration but that's a problem with fiberglass, ceramic also. IME lining increases rot because it holds the moisture within the layers. I use the poly on driftwood where I grow orchids ,broms. some are over 10 years old!!! gary