Shrubs could use some food too but there are some caveats, we’ll get to those.  Keeping plants healthy also helps lower opportunities for disease and insects to do damage.  A caveat to fertilizer response is the environment your shrubs are grown in. Woody plants respond well to fertilizers with a 3-1-2 or 3-1-1 ratio, for instance, the package may read 24-8-16, 18-6-12 or 12-4-4, etc.