Roses require a pH of near 6.5.
6.5 is slightly on the acidic side of neutral. Roses can cope with the soil being slightly higher or lower than 6.5, but may not grow well. If the soil is too acidic it may not grow at all.
If the pH in the soil is incorrect, roses will show signs of stunted growth, yellowing foliage, burnt shoots, die back and in some cases, death.
The level of pH in your soil is directly linked to the health of your plant. An incorrect pH, either above or below 6.5, will lock the 'good nutrients' into the soil and restrict the release and absorption of them to your plant. With limited access to nutrients the rose is unable to fight off diseases and pests.
It is recommended that you test your soil for its pH before you planing out your garden beds to avoid disappointment. This can be done by purchasing a pH test kit from your local hardware store. If the soil pH is incorrect, go to your local garden expert for advice on how to correct the issue, they will have more information on the specific soil in your area.
Important: signs and symptoms will vary significantly between varieties, even within similar categories. The information provided here is a basic summery of the most common affects and will not always be applicable to all rose varieties.