convolvulus tri-colour mix

Convolvulus is a trailing plant, so put it at the edge of your containers.  I would cram the containers as full as you can and either add slow release feed or make sure you feed every week.  They will need lots of water as well so water retaining gel will help. Normal spacing doesn't really apply to basket plants if you want a really good display 

Which stocks have you bought?  There are dwarf and full size but they will stand a bit of overcrowding.  Minimum hand width apart but could be up to 30cm if they are the really tall ones