Non-success with my veggies

Woe is me!  My veggie seeds are doing nothing at all this year...  Here's the problem.  We have, as I have described before, what is considered to be a 'heritage hedge' at the back of our garden.  Over the past 5 years since we've been here, we've always pruned it properly; in fact, 2 years ago we had (together with our next door neighbours) specialist arborists in to prune and remove damaged branches overhanging the 2 properties.  Because of this care and attention, it is thickening up and, consequently, giving more shade.  When we took the house over, I had new borders and beds dug, including a veggie patch (a sort-of wedge shape, 3.5 m tapering to 2 m) and got 2 loads of top soil delivered (do you know how many wheelbarrow loads that is...).  Unfortunately, once we'd got it all into the new beds (inc. the veg patch which is raised) I realised it was not very good.  Since then I've dug in compost and chicken manure pellets to improve it and have managed to produce some sort of crop annually - carrots, peas, dwarf beans, salad leaves and even a few beetroot.  This year, I've sown twice - the lettuce and spinach are finally showing a few straggly green bits, the turnips seem to be on track and maybe the carrots.  The purpling sprouting broccoli is neither sprouting nor purple, the dwarf beans have never appeared (and investigation shows they are nowhere under the surface) and there are 2 (yes, just two) pea plants appearing.  The site is netted to protect against pigeons and cats and is well watered.  Any suggestions?

(An extremely frustrated) lydiaann

PS:  However, my minaret plum was covered in blossom and, in its 4th summer, is covered in plums - Woo Hoo!!!