The idea of vertical vegetable gardening usually brings to mind runner beans, tomatoes or squashes being trained along trellises or up home-made teepees. It is far more than that though. Gardening vertically is about using vertical space in as many different ways as you can. It’s about growing plants upwards, or downwards, along fences, walls or balcony rails, in hanging baskets, gutters, over pergolas, or onto roofs. It is about using space differently, even seeing space differently in terms of how it can become productive. At the far end of the scale, New Yorkers are kicking around the concept of turning their 20-storey skyscrapers into vertical farms, and plans have been announced to build the world’s largest rooftop farm in Brooklyn. Mobile, edible walls that cost up to US$8,000 are…