Plants that keep their treasure underground need a little faith - you can’t see what’s going on where it counts most, so you’re never quite sure whether you’re about to feast like crazy or if the slugs and worms have beaten you to it. Contrarily, that’s the part I like: the big reveal at the end of the season.
As well as potatoes, parsnips and other familiar roots and tubers, there are a few lesser known subterranean harvests that really are worth giving a try.
Popular on the continent and once much-loved here, salsify is enjoying something of a renaissance. Imagine a pale parsnip with side roots and a flavour somewhere between globe artichokes, asparagus and a hint of oyster.
Growing them is as simple as it is for carrots and parsnips - thinly sow in lines in spring for an autumn/winter harvest. Boil them for 15 mins, skin them in cold water, throw them in a pan with butter, then once lightly coloured add cream, parsley and parmesan and you’ll wonder why you waited so long to try them. If you enjoyed Cleve West’s use of flowering parsnips in his Best in Show garden at Chelsea, leave a few salsify to grow on the following year - their flowers and seed heads are strikingly beautiful.
Like the potato, yacon comes from South America. Above ground it is large and leafy, with two sets of tubers beneath the surface. The larger set look like baking potatoes and these are the ones you eat.
Crisp like a water chestnut, yacon has a flavour somewhere between early apples, watermelon, pears and very mild celery, and it comes with a natural coolness and a sweet thirst-quenching juice that’s particularly refreshing. It’s easy to grow: plant it somewhere in sun or part shade and give it plenty of water. It can seem a little unwilling to get going in spring, but once in its stride it can get up to 1-2m in height. The tubers develop late, so be patient - wait til the first frosts knock the leaves back, then cut the top growth back to 10cm and carefully lift the whole plant out using a fork.
You should get a dozen or so large tubers to eat. The smaller tubers that sit nearer the surface can be saved to grow on the following year. Store the entire crown with its smaller tubers in damp compost over winter, before transplanting into a large pot in spring. As shoots appear, split the crown into individual shoots with their tubers attached and plant into smaller pots. Plant them out a metre apart when you'd plant out tomatoes, and keep them well watered.
If you like new potatoes, try oca. A few of these (usually) red tinged tubers planted in spring will give you dozens to harvest in autumn. Freshly dug they taste lightly lemony, turning sweeter if left in the sun for a few days. They don’t turn green, blight doesn’t affect them and they’re equally delicious raw or cooked, lemony or sweet. Any you don’t eat can be planted next year.
If you get to like these, there are plenty more underground treasures to investigate, Apios americana, sweet potato, and earth chestnut among them.
Mark Diacono is a garden writer and known for his commitment to sustainable and ethically produced food. He runs Otter Farm; the UK's only climate change farm and also leads the garden team at River Cottage.