Improved Regrowth is a talent in the Restoration tree, you will need to spend 30 points in Restoration to max it.
Rank table
Rank
+ Chance
1
10%
2
20%
3
30%
4
40%
5
50%
Notes
[Regrowth] has the worst mana efficiency from all of the druid's healing spells which made some players debated over the usefulness of this talent since it does not change the spell itself and requires 5 points to maximize.
However Tree of Life druids should strongly consider this talent. Considering Regrowth is the only direct heal that is avilabe for the Tree of Life without shifting out for Healing touch and thereby wasting more mana a most importantly time. Investing heavily into this talent boosts the critical chance by 50% which technically guarantees every second regrowth a critical heal. This can dramatically improve both the Health per Mana (HMP) and Health per Second (HPS) efficiency of Regrowth making it the ideal larger heal when instant cast heals like [Swiftmend] and [Nature's Swiftness] are not a vailable.