Wanted: what went wrong guide

Dr. Hessayon's Vegetable Expert and Fruit Expert books have excellent disease/pest identifying and troubleshooting sections...

Yes, Doc Hessayon's books are good but make sure you get a recent copy.  I have an old one which is great for identification of problems but the damned EU has banned most of the chemicals he recommends.  It seems we now have to ask them all nicely if they wouldn't mind not damaging our crops. :roll:

You have some very good gardening brains on this site and many years of experience.

When you have a problem just post it on here and you will immedialely get several opinions. Usually conflicting but sometimes helpful.

Often the same problem is being experience by lots of growers, may be just the weather or and invasion of a pest. Always good to share.

available at good bookstores & garden centres  rrp £7.99    

Or you can usually find them in charity shops for a quid or too, that's where I got mine!  

The problem is that all you can do is read up and then decide what might be causing the problem that you are having.

Roses get fungus diseases, often spread by aphids. What do you want to do, spray for fungus or spray for aphids? Either way you will be lucky to eliminate both. In neither case have you done anything wrong.

I grew a few orchids, if one dies then I usually find it can be for either of the following:
Too cold, too warm, too dry, too humid, too bright, too dull, too much watering, not enough watering.    
Presently have one orchid that likes warmth and light, it is growing happily next to another that likes to be cool and shady. Both are happy. One has multiplied three fold and the other is about to flower. :shock:

As for your swedes, where are they, soil type, aspect, when did you sow, when did you plant out, when did you harvest, did you fertilise (what with?), what was in the ground last year. May be stupid question did you by chance pick a small variety(lots of them these days). Disease and pests will cause plants to be small so pests and diseases are relevant. So is there sign of pest attack or disease attack?

A Where did I go wrong list will have every option possible in it, usually contradictory reasons.

Hum, its never straight forward, is it! I do find the advice on this site invaluable and usually I can find my answers by searching rather than posting - as you say we all have the same problems.
As for my swedes (as a former notherner I feel I must point out I'm using the southern term for the big purple and yellow things) the year before last I tried them in the root bed which was unmanured. I then found out they were brassicas and tried them in the brassica bed which was limed and had been maured the year before. I sowed in situe when the packed recommended. Both years I sowed snowball turnip which did fine. My main suspicion at the moment is that they were too close together  (about 10cm) also the foliage didn't get very big. I'll try wider spacing. Do you think they need a feed of some sort?

no, I did mean 10cm, and they didn't bulb out at all. Perhaps it was the lack of manure. If I use the well rotted stuff I think it would be ok with the lime I put in in the Autumn.