Leaves will absorb some nutrients. Foliar feeding gives a bush a quick shot in the arm. The effect is not long lasting though. Foliar feeding is good in the fall after you have stopped your regular fertilizing. It doesn't tend to lead to new growth but stays in the upper parts of the plant. Half strength Miracle Grow or other water soluable fertilizers and/or liquid kelp or fish emulsion added to your weekly spray program will keep the leaves greener and aid the overall vitality and health of your rosebush. Care must be taken in the heat of the summer. If done then, very early morning spraying is best. Make sure the roses have been watered well the night before. A good overhead watering just prior to the application will help prevent leaf burn. Following these practices, I have experienced no damage and extremely good results with foliar feeding. As long as I have to spray a fungicide I reap the benefits of foliar feeding at the same time.  Foliar feeding is not meant to take the place of a regular fertilizing program. It's like you taking vitamin pills or a quick sugar fix with a candy bar.