Protecting rough sawn timber used in the garden

You can get clear wood presever.

http://www.everbuild.co.uk/wood-care-range/wood-treatments/Wood-Preserver

Inside planter a couple coats of Blackjack bitumen paint, will give a planter waterproof liner.

http://www.everbuild.co.uk/901-Black-Bitumen-Paint?filter_name=black jack

 

Read their spec sheet first before deciding &have planter a few inches off the ground, & a few drainage holes in bottom, if decent size you should be able to paint the inside of them with blackjack, & maybebe surrounding underside area.

With regards to the Blackjack, many years ago I paint some timber posts with the stuff & allowed to dry before posts were concrete in,neigbour did their fence same time, some 10 years later my posts where still there, whereas neigbours fence posts had been replaced a few years earlier.

 

Any chance of that stuff contaminating the soil for growing?

Mr. HandyAndy - Really

 

for that kind of thing I use 1000 gauge dpm to line the inside of the box

 

After sealing inside of planter you could still you dpm to make a liner, or be a smart *** & buy plastic planter liners & make your planters to fit them.