During 
flowering, roses need nutrients, but with the onset of budding, only potassium and phosphorus are added. These substances help roses form a large number of buds, influence the formation of large flowers, and also help in acquiring rich colors in flowers.
In the summer, roses may turn yellow and fall off the leaves. This may be due to a lack of certain trace elements, because roses consume a large amount of nutrients during flowering.
Trace elements are applied in the form of root and foliar dressings (spraying on the leaves), while watering under the root with basic fertilizers and treatment along the crown of the bush alternate.
It is strongly not recommended to use nitrogen fertilizers in the second half of summer.