has it been very dry for a while in the growing season our dose your plot need a load of well roted manure in it,they can not grow if they have nothing to feed on.

Have you heard of crop rotation? This is the idea of not growing the same crop in the same place for more than one year, partly to prevent the build-up of disease and partly to stop the soil becoming exhausted from growing the same plants each year.
The plants you have been disappointed with are all in the brassica family and benefit from a soil high in nitrogen. The legume family (peas and beans) have roots that put nitrogen into the soil. So the perfect solution is to grow your brassicas next year where the legumes grew this year.
If you didn't grow any peas or beans this year, give the soil a good feed high in nitrogen content next year where you intend to grow the brassica family.

Hi regarding your brassica s I made a soup in a bin of all nasty weed stuff let it ferment over winter ( the smell is awful) but the result is liquid manure ( dilute to look like weak tea) very high in nitrogen and I,ve had a fab crop this year , dont forget the netting from birds and butterfly,s . the broccoli might be the later cropping kind should see some floretts in spring and early summer.
oh and one drop of cooking oil on the top of the water stops insects laying eggs in it. Nannerdigger

Thanks for the responses. We only got access to the allotment garden this June, just before the heatwave, but the plants were well watered by us and the garden owner throughout that time and we got a good crop of runner beans, which I know need a lot of feeding. We also used Growmore generally, as we didn't know how fertile the soil was. Didn't know about the nitrogen though.

We put a green manure in the bed the brassicas are being planted into next year, but do you think we should add manure over the winter as well? We will be rotating the crops, to prevent disease build up and soil starvation.