I always struggled with Plant Growth in its practical utility, but maybe I'm not thinking about it the right way. How have you used it successfully in combat? Out of combat? It always felt so niche for me.
I have been thinking about maybe making my Bard's theme "manipulation". To me, that leads to options that create misdirects or confusion vs. a straight summoner.
So for Bard spells, things like
Phantasmal Force
Suggestion - (although my DM has been harsh on this spell to date. Whenever I cast out of combat, he immediately initiates combat first because he essential gives them a reaction to my verbal spell. To me, that renders this useless because half the fun is the subterfuge).
Hypnotic Pattern
Major Image
Mass Suggestion
Hold Person
Hold Monster
With that in mind, outside of Telekinesis I don't see a ton of other options to use Magical Secrets that fit this same mold.