I would like to replace some very old roses with some new ones but, I read somewhere that you cannot plant them in the same ground as the old ones were planted in, is this true, and if so how long would I have to leave the ground before I could plant roses again!
Roses deplete all the goodness out of the soil so just planting new ones can lead to rose sickness. If you want to replant in the same place you need to remove all the old soil and replace it with new.
Dig a hole at least 60cm/2' deep and wide and fill with new soil then plant your new roses with the graft join one to two inches below soil level.
Have you tried improving the soil around your roses and pruning back?
You can buy this which is supposed to help combat rose sickness - the David Austen and Peter Beales websites recommend similar stuff.
I've not used it so I can't recommend it - I just know that it exists and I've bought some for when I dig out the straggly old rose in my garden and plant a delicious new one this winter.
Thanks for all you comments, I will certainly have a think of the best way of dealing with it.