Usable root depth
The physical bed height is not always the same as usable soil depth. Consider drainage layers, existing soil below and the root requirements of intended plants.
Avoid one universal mix
Raised-bed mixes balance structure, water retention and nutrients. Local materials and crops determine suitable proportions; avoid treating pure compost as a universal fill.
Allow for settlement
Fresh mixes settle after watering and time. A modest allowance can prevent an unexpectedly low finished level.
Practical checklist
- Keep soil below untreated timber edges where appropriate.
- Do not bury drainage outlets.