Galvanized Plant Trough

[malana3]

I will soon filling and planting up a new galvanized steel plant trough and with a view to prolonging its life feel it would be a good idea to provide a waterproof barrier between the soil and the trough. My first thought was to use a bituminous paint but I believe this may be detrimental to the plants. Confirmation if this is so or not would be appreciated. If I cannot use a bitumen material have any ABers any suggestions as to a suitable material I could use to provide a waterproof barrier. Many thanks in advance for any replies.

[Robinia]

You could line it with some strong black plastic, an empty compost bag cut open would do. Make holes in the bottom for drainage.

[SlackAlice]

Why not use an exterior oil based paint for metal work? Alternatively an acrylic car spray paint?