If all crop circles were done by plank and rope then how do you explain ghost circles?
There's numerous possible explanations, but the easiest one I've heard is that the flattened crops don't get harvested, so they go to seed in place, those seeds are left there to overwinter, and in spring those seeds germinate quicker than the planted seeds that are sowed later because they were in the ground first.
Another possible explanation is that the flattening trauma causes a chemical release in the plant that results in an epigenetic effect (changes in gene expression) in the next year's plants, triggering them to grow either slower or faster. Or the soil is more compacted there due to more people walking over it (not just the crop circle makers but tourists who come to visit the circle later). Or the fact that the crops are laid down that way provides an insulating effect to the ground over winter that changes the next year's growth. Or goofy crop circle makers (or a farmer looking to extend the payday he gets charging people to visit his crops) lays down either extra fertilizer or herbicide along the crop circle route.
Without discussing a specific event and being able to investigate the evidence and potential causes for that particular event, it's hard to know.