First I placed in some medium sized boring rocking rocks. The dw is wedge between them. Then I poured in aqua soil (not touching the sides). Then inert sand capped the top. All planting when through sand to reach the aqua soil (makes for very easy planting). At the very front, where there's very little aqua soil under the sand, I pushed in some iron capsules (3 capsules across the front). The growth rate of those plants with little aqua soil underneath has definitely been slower, but due to trimming they've caught up now.