A meta-analysis of urban farming in a variety of settings across 53 countries found lettuces, kale and broccoli were particularly suited to vertical farms. Crops like spinach can be grown from seed to harvest in 30 days, meaning a vertical farmer could have 12 harvests from the same tray each year. What"s more, if the farmer were to stagger planting their crop from one row of trays to the next, they could have an almost continuous supply of food all year round from their farm – something a traditional farmer can only dream of.