The soil had been added to as a topdressing last summer with compost I made with year old horse manure, leaves, etc. I then topdressed in fall with hardwood mulch from my local garden center. I have not tilled in anything, just top dressed.

The bed gets mostly sun to part sun (most sun in the afternoon) and sits on the north side of my house.

I did fertilize beginning of May with blood meal and potash, then the problem continued so I added about 1 to 2 Tbsp of iron sulfate to the whole bed. I also sprinkled over the whole bed some Osmocote. about 2 weeks ago. I don't want to feritlize anymore but I don't know what's causing the yellowing. It looked to me like iron or nitrogen but the bottom leaves are turning yellow now. What gives? How can some roses do fine and others not in the same bed? lol

The first pic is of the problem with the roses
The second pic is the "just fine" ones.

I am not sure of the iron diagnosis because the chlorotic leaves do not show green veins--as they would except in severe cases. The veins appear reddish on my monitor.

Usually with N deficiency the plant is evenly pale green all over.

You might want to check the pH. Residential soils can have odd spots where the contractor buried concrete, plaster, etc. Also a big rock under the plant can cause localized drainage issues.

A few solid-yellow leaves at the bottom don't necessarily mean anything.

Maybe take a closeup pic of effected leaves...