Question
When and how should you prune seven-sisters roses to shape them or should I just allow them to climb up a trellis?  I have several and they're running amuck.

Thanks for your help!

Answer
Seven Sisters rose is an easy one to prune because if you make a mistake it just grows back again. However just a word of caution here. Seven Sisters rose is a multiflora type climber which means it makes a lot of new canes which come from the base.  Multifloras bloom on second year wood. What that means is when a new cane comes up from the base in the spring, it will not have any flowers on it but the next spring the flower buds are formed and then that cane will flower. If you cut the new canes back you are actually cutting off some of next years flowers plus next years growth.  So you have to sacrifice some flowers when you prune a Seven Sister back hard. The ideal time to prune this rose is jut after it has finished blooming.
Bear in mind that you can actually cut this rose right to the base and it will come back next spring and make a lot of new canes so don't be concerned if you cut off something you didn't mean to.
Select the best main canes at the bottom and then cut out any thin, frail ones that are coming from the base. prune out all dead and also canes that have been rubbed against other ones. The cut right across the whole climber down to where you want it and finally cut back any canes that are growing in the wrong direction. Keep in mind that this is a vigorous climber and will replace quickly what you have cut off so don't be shy about cutting it back hard.