I can't help you with this one, I've never tried drying these - they're not like Helichrysum or Sea Lavender or Statice, which will dry very well. Probably work as pressed flowers I'd imagine.

ok as pressed flowers but they go brown as they fade so dont look 'pretty'.

I can't bear to take mine up, they are so pretty. -The violas will just have to wait until they have finished. I seem to remember years ago seeing some instructions for drying bridal bouquets, so maybe it can be done - why not investigate the books in your local library?

Yes they can.

http://www.driedflowersdirect.com/dried-flowers/ageratum.htm

thank you for your comments .I appreciate it very much.