Sowing biennials

I don't know the specific answer but two things spring to mind.

Firstly, as they are biennials, they will obviously grow over two seasons - one for the vegetative growth, and then next year the flowers.  That's a long time for them to be in one place, particularly if you have something more productive / pretty / colourful this year in what will be their final place.  I'd imagine that the emphasis on the seed bed is more so that they are out of the way until their time has come to shine, rather than a particular emphasis on open ground vs pots.

Secondly, as they will be in modules / pots for a long time, you would need to ensure that the modules etc are big enough and have decent compost in - multipurpose probably wouldn't do for that length of time as it dries out easily and is low in nutrients.  I'd suggest a John Innes #1 or 2 compost.

Lunarias are pretty tough so they won't mind being moved again. Here's more info on them:
http://www.plant-biology.com/Lunaria-Money-plant.php

I prefer to do sweet williams outside so they can benefit from more soil for the roots and less tendency to dry out. Plus, they love the sun. If it's new seed, you usually get very good germination so I never worry about bare spots.

Thanks guys - I'll try both in modules.  I've also got some bellis seeds so I'll do those as well. 

I've got to remove some of this year's bellis plants from pots to replace them with summer bedding.  They have got a bit of powdery mildew, but I thought if I dead headed and removed the oldest leaves and then put them in pots in a shady corner, they might be okay for replanting in autumn as well.  Quite often you can get a couple of years flowering out of biennials can't you?

I think what it is - a lot of them are effectively perennials but most people grow them as biennials as they flower better the 2nd year and then get progressively weaker (or less floriforous (is that the right spelling?)