Rose bush leaves turn yellow for several reasons; mainly those to do with too much heat. Too much shade or excessive fertilizing are other reasons rose bush leaves turn yellow.
Heat stress is common in rose bushes. This results from direct heat during sun exposure or radiant heat from the ground. Radiant heat causes the lower leaves of the rose bush to turn yellow and eventually fall off. The upper leaves become exposed to the radiant heat and the process repeats. Adding pine straw, mulch or any other type of ground protection under the rose bush solves this problem.
If the leaves do not get enough sunlight, they turn yellow and fall off the bush. This happens to leaves at the bottom of the bush when the top leaves grow large and prevent the sun from reaching the lower leaves.
Over-fertilization causes yellow leaves on roses. The fertilizer actually burns the foliage and the leaves change color and fall off the bush. This occurs with both liquid and granular fertilizer. The way to avoid this happening is to only use the recommended amount of fertilizer and to be careful not to spray directly on the leaves.
Too much water also causes rose leaves to turn yellow. If water pools underneath the rose bush rather than the ground absorbing it, it causes yellowing. The sun reflects off the water and causes overheating on the leaves, which then turn yellow. If the ground under the rose bush feels damp, it does not need water.