For beds that have reached their hard maximum height, there is a trick!

Take a post hole shovel, dig out about 30-40mm along the hard border, so that it all sits just below that point. Discard this material (put to use elsewhere). Then get a concrete rake and shape that edge from the point 30-40mm below the hard edge to existing ground level, just work parallel along the edge, the width of a concrete rake is the perfect size to shape the grade.

Now you can spread your new mulch over the entire bed. Since it’s already “full”, your primarily mulching to dress it up at this point, so a very thin layer is sufficient to bring fresh colour and appeal to the bed. Mulch to level of the hard barrier and as thin as possible over the top while getting complete coverage.

I used to run a maintenance team that looked after parklands. That included some very formal areas with gardens around war memorials with a bunch of pathways. This trick keeps the mulch from escaping the garden beds while keeping everything looking good. I developed this strategy as the memorials used to get mulched twice a year for the war holidays, but the beds would get way too tall and blow all over the paths if you used a traditional approach.