Most plants aim in life is to produce flowers in order to have them mature to fruit ( a bit like humans) - in the case of the rose its offspring is the rosehip. If you "Deadhead", that is remove dead flower heads as soon as they are past their best then the plant has not succeeded in producing its fruit and will create a new flower to hopefully achieve its ambitions. This "Cheating" of the rose is the best way to maintain a strong flush of flowers through the season (tough on the rose, but, hey, who's in charge round here anyway?). The rose will therefore soon tire of all this activity unless you feed it well and it will become poorly looking and more susceptible to disease. Apply a balanced general purpose fertiliser, or a proprietary "Rose" fertiliser in spring and again in summer. Some people recommend foliar sprays as a way to feed roses and yes, they can take in nutrients through the leaves, but generally is not worth the effort as the roots are really much better designed for this purpose. The special Rose formulations will be better for your roses as they also contain the correct balance of other minerals as well as the three main N, P & K - Nitrogen, Phosphorus & Potassium. Roses need these minerals - like Iron, Magnesium and Calcium to maintain good health.