Hi NannyOgg,
You know, it may have been one planet. As I recall, the protaganist discovers that the reason the crop is doing so well is because of some energy or phenomenon in space that unfortunately is a precursor of destruction of the planet. And that discovery was in fact the Big Reveal. I thought that he had discovered it because of it happening on other planets, but that may not be the case. I read it when I was about 10 and loved it and I want to find it and read it again and see if it still holds up.