Rampant Blooming - the only viable talent if you are playing as main support. 150 per second doesn't seem to be much but you have to remember that it stacks with passive healing - constant 80 HP per second. So it gives 230 HP per second as addition to 900 burst healing. Now it sounds cool.

Verdant Expanse 5 - I think it doesn't need any explanation. Every healer with area healing needs it's range to be maxed.

Perennial 5 - I've seen many people, even pro players, who prefer to have this card on level 4. Personally I don't agree with that. When it comes to self-sustain and saving your teammates, every 0.5 second is valuable. I also have to mention something here. You need to have a good timing with healing, don't try to heal while ally has Cauterize on. While in early game it doesn't mean much, in late game you heal like nothing and you waste your ability. So it's a good tactic just to wait until Cauterize is ended.

Adrenaline 3 - the most underrated Grover's card. With a good team, passive healing gives Grover asist after asist and all of them reduce cooldown of Blossom by 3 seconds when you use Adrenaline 3. Less of cooldown, more healing, right?

Barkskin 1 - just a little filler card that gives you some more self sustain (2375 is more than any other healer in game).

Vine Grasp 1 - another filler card that allows you to escape from dangerous situation more often.