Does the second aspect of the Plant Growth spell (enrichment) stack with itself since the spell is an instantaneous effect (sort of like how the damage from multiple fireballs stacks)?
For example, if a druid were to cast Plant Growth on a farmer's crops 3 times, would said crops get double their normal productivity?
What would happen if a druid/ranger cast this spell on their crops multiple times per day? Wouldn't said character essentially be able to feed a small nation single-handedly?
I probably wouldn't allow a single set of crops to be "enriched" more than once, but that's fine because in most situations you can just move on to the next half-mile.
Considering the spell essentially takes a year to work, I'm going to say that a character could basically spend their time and spells going to from place to place casting this. Depending on the farm area, a month or two a year could keep everyone very well-fed.
Ah, plant growth... the spell that was overseen by the Pathfinder nerf crew and still limits movement to only 5' per round for only a 3rd level spell, while Solid fog only reduces movement to half.