What to fill a raised veg bed with?

DiggerUK

dllive said:

Now you need to be introduced to the world of 'skipdiving'. These are treasure troves. Get some plasterboard, same size as your plot, score it with  a Stanley knife in to chess board sized squares on both sides, crack it up  and dig it into what soil you have there, at least 30cm/1foot deep. Or you can simply buy some Claybreaker..._

Very interesting! Why does this benefit the soil?

Plasterboard is 98% Gypsum, it 'flocculates' clay and helps break it up. 

The science of flocculation is above my pay grade, but that's what it does. It is different to garden lime because it is neutral, not alkaline, so can be used safely with acid loving plants, and it's free, go online and check out the cost of buying Gypsum. Also, potatoes  react badly to alkaline soils. 

It seems you have a lot of ground to prepare from the picture. Keep adding compost, if you scrounge rotted horse muck you'll get good soil for free, plus the hard work of course..._