Prevents Regrow Bloons from working while in the radius of the Village.
~ In-game description
Grow Blocker is the first upgrade of Path 2 for the Monkey Village in BTD6. It causes all Regrow Bloons (including Camo Regrow Bloons) to stop regenerating within the radius of the Village. Once bloons exit the radius, they are affected for another three seconds before they will start being able to regen again. Affected bloons have a red pulsating outline of the bloon, signaling the Monkey Village's effect.
Grow Blocker is a low-cost upgrade mostly relegated to preventing the growth of Regrow Bloons within range of the Village. Otherwise, it is served for locking the Monkey Village towards Grow Blocker's superior subsequent upgrade, Radar Scanner, which grants camo detection to nearby towers. However, the Grow Blocker upgrade is still a viable choice for reducing the strength of Regrow Farms within specific locations.
This upgrade is useful against rounds that contain high amounts of Regrow Bloons, especially against Round 76 and 79. Similarly, the Grow Blocker upgrade is useful on specific challenges where All Regrow is enabled.
As a rather cheap upgrade leading towards Radar Scanner, this upgrade comes in handy as a method of reserving Path 2 for a particular Monkey Village. Purchasing Grow Blocker makes it easier to specifically choose a specific crosspathing for the subject Monkey Village without needing to remember from the top of one's head. Generally, one would purchase Path 2 mainly to purchase Radar Scanner later on in the game, whether it be only with Path 1 (typically with Jungle Drums or higher) or with Path 3 (typically with Monkey Commerce or higher).
The reason why this specific upgrade doesn't get much use is because the bloons that are affected by it, are either too weak (they get popped before any regrow happens, preventing grow blocker form actually doing anything) or too fast (they move out of range and there for grow back layers) or both.
No significant changes were made to Grow Blocker since it was first released in BTD6, although there are some bugs currently in circulation. More details are to be added about some bugs that were discovered and possibly patched later on.
[Unknown] Upgrading a Grow Blocker will cause all Regrow Bloons within range of a recently upgraded Village (even towards Radar Scanner or its further upgrades, or even any non-Path 2 upgrade) will permanently stop regrowth.
Beacons from Grow Blocker Villages spinning around recurringly
Crosspathing in BTD6 (Top: Path 1, Bottom: Path 3)
Grow Blocker (along with its subsequent upgrades) formerly was the only upgrade that can add "Grow Blocked" status effects on bloons; this was no longer the case when Ezili arrived in Version 7.0 with her Heartstopper ability, a global variant of Grow Blocker.
In BTD6, Grow Blocker has the lowest XP requirements to unlock for the Monkey Village, at 150 XP. The second-lowest goes to Bigger Radius, requiring 160 XP.