Has anyone tried this method for creating a hosta bed? I'm wondering how long the raised bed would last before the logs decayed and the bed would eventually level out. From a little research it is supposed to add nutrients and control moisture.

A few years ago I made a bed using the lasagna method, layering soil, wood chips, compost and leaf mold. The hostas are doing great there but the media has sunk almost six inches in four years. I may have to dig out all the hostas someday and add soil or more lasagna material to bring it up to height.

If i used green logs of Black Cherry I'm wondering how long they might last.