I would use a turf type fertilizer on boxwoods. Products with a 3-1-2 or 4-1-2 ratio of nutrients provide good health and vigor. Examples include 15-5-10, 16-4-9 and 21-7-14 or anything similar. The fertilizer for trees and shrubs is fine too. Just apply it at the label rate and then water it in well. Water those shrubs every week or two depending on the temperature and rainfall. Provide a good soaking when you water and the allow the soil to dry out a bit before watering again.
The following web site provides detailed information on how to root cuttings of roses or other plants too for that matter:
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