I thought it was the opposite

I read an artical by a well known gardener, the first thing that I came across was about Pelargonium, where he said he doesn't feed them, yet I have always thought Pelargoniums were gross feeders. The second was about legumes, advising planting  brassica after them as they add nitrogen to the soil, again not what I thought actually happens, I thought that the plant used up all the nitrogen producing peas or beans and if you wanted nitrogen you had to dig the plant in before it started to produce a crop
So have I got it wrong with the two of them?

From what I understand, most of the nitrogen ends up in the peas/beans you take off the plant, so yes it's best to chop them before they flower to maximise the nitrogen going back into the soil.

Don't know about pelargonium but agree about the legumes which is why I grew lettuce in the shade of the bean poles - shade and nitrogen, although I doubt the lettuce roots go far enough.

If you look at the roots of broad beans for instance you can see the nitrogen nodules. If you cut them off at ground level once they are finished this nitrogen should release into the soil as the root dies? Its a minimal amount and hardly worth the bother tbh? 
Put the roots on the compost heap and the nitro will help activate it.

Most flowers are usually treat 'rough' with no fertiliser I always thought?

I don't think the nitrogen stays in the nodules, it's just made there and ends up in the seeds of the pea/bean pods.

Well I follow Fibrex - they have some amazing plants. They say they don't need too much nitrogen but a high potash feed weekly does the job.

https://www.fibrex.co.uk/blogs/news/wint...largoniums