Start with the site
A bed over free-draining soil has different needs from one on paving or a roof terrace. Water needs a safe route away without carrying soil into drains or neighbouring areas.
Use liners for a defined reason
A permeable liner can retain soil at open joints, while a suitable internal barrier may protect some bed materials. Avoid sealing the base unless the design is specifically intended as a container with controlled drainage.
Keep usable depth honest
Drainage layers and false bases reduce the volume available to roots. Enter the actual soil depth in the calculator rather than the full outside height of the bed.
Practical checklist
- Keep drainage outlets accessible.
- Check load limits before placing deep beds on structures or balconies.
