With the floor lined with landscape fabric, you're ready to add soil to the raised flower bed. The planting-bed area has a depth of 14". That's a lot of space to fill, so you'll want to mix generous amounts of peat moss, perlite or vermiculite into the soil that you're using. Any of the three will lighten your soil, allowing it to breathe better. Peat moss, perlite and vermiculite also help your soil retain moisture.
Perhaps you're wondering, "Why build a raised flower bed with such a deep planting area?" If you've ever had a container garden (which this raised bed could be classified as), you may already be able to guess at the answer. The soil in most container gardens has a tendency to dry out too quickly. That's because their soil lacks sufficient mass. As a result, you end up having to water frequently, which may be inconvenient for you. But the 14" depth of our raised flower bed affords us a soil-mass that will retain water well.
We had old styrofoam around and decided to recycle it as filler. I'd avoid using it in a planting bed for growing vegetables, but the structure for us is purely a raised flower bed. We broke up the styrofoam and put it down for a first layer, where it will provide good drainage and aeration.
We then filled our raised flower bed with soil, which was mixed with peat moss to lighten it and with compost to enrichen it. As you can see from the photo above, we wasted no time planting in our new raised flower bed!
