Carrot bed

I'm considering making a raised bed with some surplus wood from an old pergola to grow some root veg in. Has anyone  done this? I'm on stony clay so will require some different soil to fill the bed with. Has anyone got any recommendations as to what to fill the bed with as cheaply as possible?

Sieve the garden soil and add sharp sand and some sieved compost. I would go for equal parts of all three.

Thanks for the advice, I've started sieving the soil which will be the bottom of the bed and I'm liberating a lot of Stone which is good, but I'm going to have to come up with a plan as to what to do with the stone. I've currently got a small cairn of medium to small stones and have only just started. Anyone got any thoughts as to what to do with stones other than Tey and lose them elsewhere in the garden?

If your soil is poorly drained and your bed is quite deep you could always utilise the stones at the bottom of the bed with a blinding layer of cardboard over them before adding the sieved topsoil preferably mixed with builders sand?

If you can get some dried seaweed I’d dig that in as well.

I plan using an upside down planter for this next year, picture below.

I currently have old veg foliage in there rotting down, will then add spent soil/compost/grass clippings and anything else I can get for nothing

Will probably sow in stations through a top layer of cardboard.

Good luck