Welcome to NGA,
@morgie !
As a person who has made the mistake of planting in a spot that did not drain well... I would advise digging out the rose bushes and planting them (temporarily) in large pots while you amend the soil in the garden bed. I would say you need to dig down probably 1-1/2 to 2 feet and add a LOT of organic material to your soil, perhaps even some sand (which is what we did, with good results). It took some time, but our garden no longer has any standing water, even with a lot of rain. And, as Rick said, adding some trenches to direct water away from the planting area certainly couldn't hurt.
It would probably be helpful if we knew more about where you live (and garden) -- you can add that info to your "profile" and it will show up on the right-hand side of all of your posts.
I hope this is helpful!
