We have been doing green roofs for 5 years now and have tried a number of different types of edging. We started off using old scaffold boards but have recently started using gabions filled with stones because of their low maintenance requirements.
In order to improve the wooden edged roofs we are now using a new material to replace the top edges which are most exposed to the elements and tend to weather quite quickly.
Before: Scaffold boards cut in half along
their length, the top edge has weathered
After: Top edge replaced with recycled
Detail: I have left gaps between the
planks to allow for expansion and
filled with flexible roofing sealant.