I have an existing 40x5 foot bed with 30 DL and perennials that I put in last year. I want to extend the bed by 10 feet on one side. I was going to try the lasagna method as I purchased 10 plants yesterday which I want to plant immediately. Since the plants are potted with 6" of soil, how deep do I need to make the "lasagna"? Also, this method will likely result in the new bed being higher than the 40' bed made in the traditional way. I have cedar logs outlining the original bed. I could leave the cedar log on the end where the extension of the bed will be and I could use a higher log to accommodate the deeper bed. How deep should the lasagna be? I have finished compost to use.