Intrinsic, first, a plant that is buggy shouldn't be fertilized..
What type of holes? are you finding? Are they small or large bitten foliage?
If large, then I'd think something like a rabbit or squirrel is snacking on your hib.
If small, then your hib might have an insect/s. There's many pests to check for including mites, mealy, whitefly, scale, etc.
Do you know how to check for pests? Mites build webbs, looking similar to the common spiderweb, but finer. Shake the plant to check for any white bugs flying in the air. (whitefly)
Inspect entire plant for anything that shouldn't be there.
Mealy are cottony patches. And scale remsemble armored, roundish pests. Scale is difficult spotting at an early age..But once they mature they're easy to locate. Most bugs leave a sticky residue. FEel the leaves/stems for stickiness.
BTW, are your 4 hibs the same type? Toni