I wouldn't even do ornamental gardening in them because I just don't want anything leaching whatever comes off them anywhere on my property. Decided on no railroad ties anywhere for the same reason.

Maybe today that spot is ornamental only today but long term I want to replace 100% of ornamentals on my property with functional plants. It also means any future excavation I have to think about what to do with that dirt. Right now, everything I dig stays on site and when the pile gets big enough it turns into a new raised bed.