Posted: 18/04/2014 at 12:42
It depends on how good the soil is. If it's poor to medium fertility I would restirct myself to one plant per post but if it's good soil I'd plant two, maybe a rose and a cleamtis that would compliment each other in colour or flowering period so maybe a clematis for April/May and a rose to take over flowering from late May and June.
Whatever the case, I would prepare really deep planting holes back filled with added garden or bought compost and some well rotted manure if possible. Plant clematis at least 4" deeper than they were in te hpot and roses with the graft join 2" below soil level. Soak the pots throroughly before planting out and water generously once planted. Feed generously every spring and mulch every autumn.
I would also stretch wires horizontally between the posts to allow the roses and clems to spread their stems horizontally as well as vertically as this encourages more flowers to form.
Depending on how exposed you are you could consider grapes which would give you a crop as well as as attractive foliage. Wisteria is very good on pergolas as long as you follow the pruning regime to encourage flowering spurs.
I think honeysuckle is best on walls or trellises but you could look for forms of that which please you. You could also grow morning glory which is a tender annual so would allow you to have different colours each year.