So here's something funny. There's a a short 25-minute making-of video on Netflix and it's divided into segments e.g. "Veldt" or "Jimmy" and then you get to this:
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That's right, they devote time to talking about just the wheat (they planted it all themselves). At one point Deborah Snyder says ""Wheat is this character in our film and it was super important that the wheat be real because we wanted to actually harvest it and if it was fake we couldn't actually cut the wheat and bundle it. It wouldn't have been realistic" and Snyder adds "One of the things that actually drove the schedule was where the wheat was at its correct ripeness for harvesting". And then a producer goes "we let the wheat tell us when it would be ready to be shot".