Posted: 04/02/2015 at 10:17
I have a bed similar to yours. Mine is in semi shade and the clods of clay I was lifting out of it were so dense, I could have almost made a pot out of it!
I got really fed up sifting in good stuff, turning it over, breaking it up etc.
In the end, I took the decision to empty pretty much the entire raised bed completely and start again.
I only left perhaps 20cm or so of clay at the very bottom, which I had turned, raked, broken up etc.
Back filled the rest of the bed as other s have suggested - grit, good quality compost, some manure.
My roses, by contrast, are in in the open ground (not the raised bed) in clay soil - I have turned it over so many times and add manure every year, but it is still heavy. They love it, no complaints!
My rosemary and lavenders and any other mediterranean plants were suffering in the ground, so I stuck them all in a big planter, half backfilled (as Monty advises) with broken crocks, The rest gritty soil. They are now thriving.
You can put mediterranean plants in a raised bed, provided drainage is excellent and as someone on here has said, add loads of big pieces of material around the plants and keep them near the front. Personally, unless I am doing a 100% mediterranean plant raised bed, where I can get the conditions perfect for them, I don't bother and always stick them in pots instead.
If you soil, in spite of you efforts, remains fairly heavy, go for perennials that don't mind those conditions (as someone else has said). In my wetter, heavier and shadier parts of the garden, I have real success growing ophiopogon (black grass), as well as Japanese anemones, heucheras, hakkonechloa grass, cyclamen hederifoliums, snowdrops, ferns of various types, aucuba and astilbes. Worth pointing out though that the garden drains well now, even though it didn't used to. There are few plants I know of, except certain irises and ophiopogon grass, that will relish sitting in water.