This is great, and I have some recommendations!
1. Plant Reproduction
Once Hedges or Brambles grow past their maximum stage, instead of getting stronger, what if they spread, making a minimum-stage bramble/hedge on a nearby empty space? That would allow for some kind of farming. I think that's a good thing, since it is a garden after all. Maybe it would only work if they had another of their own type nearby.
2. Plant Regrowth
I thought it would be a cool idea to die HP to growth stage. That way, plants would be able to heal themselves (Like in real life.) But they would also lose their abilities or strength the weaker they got. That sounds like a really cool mechanic that would further separate it more from the possible inspiration of this game.