Soil is arguably the most important aspect of a successful garden and the produce from your garden will only be as good as the quality of the soil selected for it.
gmTANKS recommends using a good quality composted garden soil to fill your garden bed. gmTANKS raised corrugated steel garden bed is also suitable for a “no dig” style garden.
Remembering that the advantage of using a raised garden bed is the improved drainage it is essential to use mulch on your garden to retain soil moisture.
It is not uncommon for people to want to half fill their garden bed with brick rubble; this can have the disadvantage of over draining the soil as well as migrating through the soil over time. Similarly, there are sites that recommend placing hay bales in the bottom of your garden bed, while this is a legitimate technique the hay bale will break down over time and you will need to keep topping up the soil level.
If in doubt, contact your local nursery for professional advice to ensure you get the best results.