So far we have set up seven (of a planned eleven) raised beds, c. 1.4m (width) x 2.6m (length) apiece.
All were made with compost placed directly onto the ground at different depths, without cardboard. Four of the seven have the garden’s most copious weeds, dandelion and creeping buttercup, coming through.
Each of the four with weeds growing through were made partly or entirely with a medium grade, organic woody compost from garden waste, which we now know does not have the density to provide sufficient ground cover to suppress weeds at a depth of three-four inches.
Of those with none coming through (so far), two have either the benefit of depth (five-plus inches deep); and another is made with a higher grade, finer compost that works very well as a barrier for suppressing weeds (as well as being the best growing medium for carrots, parsnips etc).
So we have had to buy more finer grade compost (Envirogrind soil improver) to top off the cheaper, woody compost to suppress weed growth (while enriching the soil).
The lesson learned here is that we should have purchased a higher grade base compost to begin with.
Also, adding a cardboard layer first would have helped to suppress some weed growth. We dug out the shallowest of the beds with the woody compost after the fact to insert a cardboard layer. This bed is intended for onions and spring onions, but also leeks – so the cardboard restricting depth might be problematic later on…