Question: When should I fertilize shrubs that bloom in the spring, such as flowering quince, forsythia, bridal wreath, weigela and azaleas, among others? What should I use?
Answer: It’s usually best to apply a lawn-type (high-nitrogen or all-nitrogen) fertilizer immediately after the shrubs finish blooming. You do that in conjunction with pruning and re-shaping, to stimulate vigorous new growth over the ensuing several months. You might make a second application in very early summer. By fall you’ll want to switch over to a complete-and-balanced analysis or even a high-phosphate fertilizer to promote good flower bud set before winter. A soil test will give you the best answer for your specific needs.