Anything light blue honestly. I still can't believe there's not a single light blue flower in the entire game. The only thing that comes close are blue hydrangeas...
I'd like to see vines introduced that grow up structures they're planted next to. That would include morning glories, wisteria, ivies, and a new variant of rose.
sunflowers, cacti, orchids, and more colours for all of the flowers! :3 I always felt like there was too little of colors to choose from, especially since they're limited to certain flowers.
i have thought of some new ones id like besides the normal sunflowers and stuff ect, id like morning glories that actually grow up the side of your house or tree, and some flowers that can provide some sort of ground cover being low and flat and covering an area around it <3