I would say, for me, “Growing things makes me happy” and “Growing things make me happy” (diagramming those sentences being left as an exercise to the student). I’ve had plant companions since I was a student at the Naval Academy (yes, midshipmen were allowed plants, even back in the ancient days of the 1970s), although only a few cactus made it through my time on submarines (and even those only with the help of a neighbor with my house keys). I’m bigger on flowers now than I used to be, because: Debster.