A bed whose shorter side runs well past ~1.2 m has interior ground that can't be reached from its edges.
Promising · suboptimal if ignored → advise
How it works
A comfortable arm's reach is ~0.6 m, so ground more than twice that across can only be tended by standing on the bed — which compacts the soil and breaks the structure the bed exists to protect.
What to do about it
Make a wide area into several beds with a path between them, not one bed you step into. Beds are individual entities here — there is no sub-bed to carve, so add another bed instead.
The evidence
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Iowa State Univ. Extension, Yard & Garden FAQ, raised bed size (read 2026-07-21; read by the maintainer 2026-07-25): 'Beds accessible on both sides can be 3 to 4 feet wide'; one-sided, 'the maximum width should be 1 1/2 to 2 feet (i.e., approximately arm's reach)'.
Univ. of Minnesota Extension, Raised bed gardens (read 2026-07-21; read by the maintainer 2026-07-25): 'the reach of your arm is generally a good metric ... If you can access both sides, the bed can be up to five feet wide.'
The two sources DISAGREE on the ceiling - Iowa State's 3-4 ft against Minnesota's 5 ft - and this rule takes the tighter one, so its ~1.2 m threshold is a judgement between published figures rather than a number either source states. That is why it is recorded here as promising rather than well established.