Nitrogen fertilizer makes the foliage green. The more you apply, the greener the foliage, but don't expect to see many blooms. All of the plant's energy is being used to promote green growth, not flowers.
If your existing one has many flower buds, and you prefer flowers, rather than a green shrub, adding a layer of compost around the plant once or twice a year, spring and/or fall. is all that's necessary for a healthy plant.
The one's you recently purchased, were probably fertilized to produce lush green foliage, which would attract shoppers.
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