Ground work.

I have two raised beds 3f x 8f x 8inches deep and I fill these with general compost renewing 50% every year in the spring. I've been doing this for two years growing root vegetables in one plot, brassicas in the other, changing the plots over the following year. Whats happened?

Carrots: Grow very well always a good crop.
Beetroot: Once again do just fine.
Turnips: Rather small just larger than a tennis ball.

Cabbage: Never "Heart" sometimes do cheat on spacing by a couple of inches....it's a space thing  :blink: We just eat the leafs.
Cauliflower: Grow large enough for two people, one and a half times a tennis ball.
Brussels: Just the two last year because of space again. WoW! a realy good crop.

As you can see I seem to have a size problem. 

The queston is. Should I be doing more ground work? Thanks.

Well you are obviously doing something right! Thats not too bad

Cabbages need to be planted in firm soil (which you are doing with your sprouts) and they do like space. 18 inches between with my primo white cabbage is the recommended spacing. They also like a bit of lime added, so its worth doing that in your brassica bed a couple of weeks before planting. I would also use well-rotted manure on two beds every year (not the carrot bed obviously) for extra nutrition, as general purpose uses up its nutrients after 6 weeks or so. Onions like a bit of space too but I cant remember how much off the top o fmy head

Onions are 3-4" - I planted mine out yesterday and gave them 4" to be safe

I remember Eden Project had a fine display of blown cabbages last winter: they'd put them in a newly dug, freshly manured, light soil on a slope.  Oddly enough, they didn't heart.  I think the treading firmly, and maybe being stingier with nitrogen, ought to help; cabbages need less fertiliser than caulis, so that may be part of it.