This is a handy chart for calculating how much produce can be grown in a given space using a bed system.
It’s from the book Solar Gardening: Growing vegetables year-round the American intensive way by Leandre Poisson and Gretchen Vogel Poisson (ISBN 0-930031-69-5).
For a printable PDF copy, click here.
The chart shows the average yield for a 4′ x 8′ bed (32 square feet, or about three square metres). Depending on the conditions, the yield can be higher or lower than this. Last year we harvested over 30 pounds of potatoes in one of our allotment beds (which are slightly smaller than 4′ x 8′). Conversely, there’s no way in a British climate you’ll be able to grow 28 pounds of watermelon or 45 pounds of sweet potatoes in a 32 square foot area!
It’s a great starting point, though, for figuring out how much space to dedicate to each crop.