How to seal an indoor wood planter box?
I have made a few exterior window boxes and none lasted long with the wood in contact with the soil. I would make the boxes of whatever wood and finish matches yor kitchen. I would seal the inside with an exterior grade urethane. The idea is to protect the wood from the dampness and occasional water spill. I have had the best long term results by using a plastic container to hold the soil. The box is just a decorative holder for the plastic containers