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Dogwoods should be fertilized once or twice a year. However, not just any fertilizer will do. Dogwoods evolved in very specific forest conditions and are flowering plants. They therefore have very specific fertilizer requirements that will not be met with a standard "one-size-fits-all" lawn and turf fertilizer. Aside from the formulation, the method of fertilization differs from that of your grass. In order to give your trees the most benefit, the fertilizer must be placed below the grass roots.
To find out how to obtain fertilizer specially selected for use on flowering dogwoods trees, click here.