Wait until its first flush of flowers is over, about July. Then prune it back to 6" below whatever height you want, always pruning to an outward-facing bud. You will inevitably lose some flowers, but it will soon produce more.
Karen, cut back the branches that are dying back to a healthy out growing bud or take it right back to the base. At the same time take out any ingrowing thin branches to give the plant air in the centre.This will not cause any problems with the flowering and it is better to get rid of any disease that could cause further trouble.
Kevin Eastment wrote (see)
I Have got 6 rose plnts comming (bear root) I want to plant them in pots what do i buy to plant them (compost or somthing eles)
John Innes No2 compost, Karen.
Thanks for the feedback Frank. David, unfortunately I'm not in the UK, don't know how to find John Innes of any variety.
Garden centre, DIY store,
When do I prune a climbing rose that is growing over a porch. Is it best to wait until the Spring