It's been about a week since I planted the petunias and they are growing very well and the leaves are not yellowing from the constantly moist soil. The flowers seem to be thriving probably because the medium had fertilizer already in it. I planted some spinach mustard seeds along the ends of the island to see how they would do. Maybe strawberry plants next year in a setup like this. I did put a piece of 2"x14"x 4' foam under the center of the island to push it up a little so as to not flood the medium quite so much.