Grass runeys are, in my opinion, the toughest to revive out of them all.
The easiest way to revive them is to find a part of the town that has no Tree runeys, and place several of them there. Make sure to have a lot of Water or Rock runeys around, since they won't grow unless there is more of another type of Runey. That area should be filled with Grass runeys in about a week, if you keep the number of another type of runey except Tree runeys up.
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