Meanwhile, having checked the courgettes on arriving at the plot, they have very often produced marrows (almost) before I leave. I swear that if I had time to stand and watch I would literally be able to see them growing. Can someone explain to me how it is possible to go over each plant, leaf by leaf to ensure that there are no more courgettes left to pick, but two days later there are marrows more than a foot long? Where do they hide?