Answer: Viburnums can be either evergreen or semi-evergreen. As such, the oldest leaves eventually fall off and can leave some bare spots. Since these plants flower on new growth you can take care of both problems by pruning them back. Wait until the flowering has finished and then prune the shrubs back by a few inches to one-third of the length of the branches, depending upon their current size and appearance. Pruning will encourage the development of healthy new branches and will force growth back towards the center of the plant to help it fill out a little more. You should see a bushier shrub by late this summer and lots of flowers next spring. Feeding is a good idea - don't overfeed, though, or you'll risk burning the roots of your plant and stopping new growth althogether.
Best wishes with your viburnums!
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