When the soil warms up this month, it is time to sow many hardy vegetable and herb seeds. But how to tell if the soil is indeed warm enough? Farmers in some parts of England went into their fields, dropped their pants and sat down bare bum. If this was comfortable, the soil had reached the right temperature. Urban gardeners should only attempt this after nightfall lest perturbed neighbours contact the gendarmerie. Of course you could invest in a soil thermometer but that’s not half as much fun . . .