Hi, I am getting a nice planter structure build of fir wood. Not sure
what kind of fir.

I am not sure if I will put on concrete or the lawn yet, but I would
like to add something to protect the wood from weather and watering.
But the protectant should not contaminate the soil that is below it or
the plants in the planter.

Any suggestion? I heard linseed oil would be good? Where do you get
it?