So he's had the farm for quite some time, but had a local guy managing it, who then informed Clarkson that he would be unable to continue managing the farm. So Clarkson got the idea he'd just do it himself (while doing yet another 'reality' show of him attempting to do it). That's where the kid Caleb came from, who helped the other guy run the farm. It's not clear actually how long Clarkson's had the farm, but while he was trying to open the farm store, and getting council approval, they did show the snippet of Hammond and May blowing up his house, which was apparently on the farm?
It's a great show. Clarkson has his moments (screaming liberal), but he's fun to watch. Only he could find a Lamborghini tractor......who knew.