Possible Causes of Yellow Leaves and leaves falling off on Rose Bush
Rose leaves turn yellow and fall off at the bottom of the rose bushes at times when the upper leaves are shading them. The lower rose leaves are not getting the sunlight they need to, so the rose leaves turn yellow and drop off.
Another reason for rose leaves turning yellow is the rose bush is under some sort of stress. A common cause of stress is heat stress. The rose bush turns yellow and drops its foliage in an effort to cool down in the case of heat stress. Sometimes with other stressors the rose bush will start dropping foliage until the stress is relieved, whatever stress that may be.
Yellow leaves on rose bushes may also be caused by radiant heat. The ground or area below the rose bush is retaining too much heat, which then radiates up into the lower portions of the rose bush. This radiant heat causes heat stress and the lower foliage will turn yellow and fall off as the rose bush tries to protect itself and de-stress. Dark colored mulch or some rock mulches can hold too much heat in and reflect it back at the rose bushes. If there is a dark mulch or just the bare ground below your rose bushes, try using some shredded cedar mulch or some other light colored mulch all around the base of the rose bush, 24 inches in diameter for younger rose bushes.
Another source of reflected heat that can cause yellow rose leaves is water. If rose bushes are watered and the water is left to sit at the base of the rose bush, such that the sun’s rays are reflected off of the water and up onto the lower foliage, the lower foliage will be somewhat burned by the reflection of the sun’s rays. Thus, the rose foliage will turn yellow and fall off. To avoid this, keep your roses well watered but not soaking wet, and keep an eye on the soil moisture. If you do not have a moisture meter, just stick your finger into the dirt as far as you can. If it feels moist, there is no need to water the roses just yet.