It's all very well all the smug gardeners you know going on about which heritage veg they are sowing this year. But what happens if all your outside space is covered in Tarmacadam, thank you very much? And located a handy seven flights up? In the past, you'd have had to pick your way through conventional veg-growing books to find the little bits that apply to you, fast-forwarding, wistfully, through the sections on double-digging and where to put the compost heap.
Finally, though, someone has devoted an entire book to the subject of how to get things to grow in an entirely container-based veg plot: Alex Mitchell, acclaimed author and veg expert (and also a very good cook – not that this sways me in any way). The Edible Balcony is full of useful information, but also beautifully illustrated with pictures of how your tiny rooftop can look once it becomes an urban oasis. There'll be beanpoles hiding the tower blocks, thyme hanging off the railings and a peach tree flowering in the sunniest spot, if the book is anything to go by.
But how did she find all these brilliant, but tiny, plots? "The logistics were fairly challenging," she laughs now. "I spent hours trawling the internet, finding projects such as Project Dirt, based in Wandsworth, which is doing amazing things. I even found some growers who'd made an urban orchard balcony. And then I'd get to meet them. If they were in London," she adds, with a smile. "I didn't actually get to Dubai or St Petersburg."
She is clearly inspired by the inventiveness of these urban growers. "There's a kind of energy to gardens in a city, that's what I liked the most: people buying pound-shop storage boxes and growing them full of fresh produce. And doing things in such tiny spaces." She's hard-pressed to name her favourite, though she has a soft spot for one in particular: "Tufnell Park Mark! Mr Heath Robinson Extraordinaire. He is mental in the best possible way: he has the most incredible balcony, crammed with things. He showed me how to grow sunflower shoots, the seeds you buy in health-food shops grown for three days, which have an amazing, crunchy, nutty taste."
As far as she's concerned, though, there are some areas of the veg-growing bible that can stay exactly the same, whether your plot is high or low. "Ultimately, there is only one way to sow a beetroot seed and only one depth to do it. But I enjoyed the process of experimenting with rooftop growing – I made everything at home; I just hate going to shops. And it's amazing to discover there's lots of new crops with potential for city balconies and rooftops – tender things such as guava, from Chile, which had an appeal for me because my grandmother is Chilean; cape gooseberries, those little, pretty, lantern-shaped fruits, which are really easy to grow; and cocktail kiwi, as tiny and delicious as they sound."
'The Edible Balcony: Growing Fresh Produce in the Heart of the City' is published by Kyle Cathie, priced £16.99
Alex Mitchell's top tips
1. containers Make them as big as you can from galvanised dustbins or those trugs you get in DIY shops. For plants that need lots of water, look for something deep. Drill six to seven 5mm holes in the base for drainage.
2. vertical space Criss-cross grilles will work for peas, squashes and beans, growing upwards. Guttering fixed in rows will give you more space for baby salads, and you can grow herbs in hanging water bottles.
3. mulch Containers dry out, so use shingle, say, on the surface and you'll have to water less. It also looks smart. And choose crops wisely – carrots, beetroot, chard and chilli are not so desperate for watering.