Sorrel is a perennial vegetable that takes me back to my childhood. Roaming the hills above our house, thirsty from having forgotten to take water, I would seek out the apple-green leaves of Rumex acetosa. They did nothing to really stop me getting dehydrated I’m sure, but the rush of saliva brought on by the acid taste always made me feel better. We called them souries (pronounced soor-eez) from the sour taste, but the more widespread name is common sorrel.

Sorrel is a taste-name rather than a strictly botanical one: the various plants that are called sorrel are not all related but do all share that same sharpness, produced by the oxalic acid in the leaves. The oxalic acid means that it isn’t wise to eat sorrel in large quantities as it binds up calcium and can cause deficiencies, as well as contributing to diseases like gout. In small quantities however it is fine and in fact there is a small amount of oxalic acid in many accepted food plants including spinach and rhubarb.

Several of the sorrels are in the Rumex genus. Sheep’s sorrel, R. acetosella, is tasty but probably too small to be worth cultivating deliberately. Buckler-leaved sorrel, R. scutatus, is also small-leaved but very productive and the leaves with their cool shape look great in a salad. My old friend common sorrel, R. acetosa, is the one that gardeners have paid most attention to and there are many cultivated forms, bred for larger leaves, mostly going by names like French sorrel and Polish sorrel. There is also a non-seeding form called ‘Profusion’ which is available from Poyntzfield Herb Nursery – ideal as it puts all its energy into producing leaves.

Other sorrel-tasting plants are in the genus of Oxalis. I don’t know whether Linnaeus named the genus after the acid or whether it is the other way around. Oxalis is a huge genus with around 800 species, variously known as sorrels (which they aren’t), shamrocks (which they aren’t) and grasses (which they aren’t). Confused? You will be with common names.

As an aside, the genus includes Oxalis tuberosa or oca, an important root crop in the Andes which could also be grown here if only they could find a day-neutral variety. As it is, it only starts to form tubers when the day length drops below a certain critical number of hours, fine for the Andes but not much use in a climate where the first frosts might well be in September. I grew it productively for several years until an early frost wiped out the lot. All is not lost, however: it was the same story with the original potato until a mutation made it day-neutral and allowed it to conquer the world.

The only Oxalis I have in my forest garden is O. acetosella, the native wood sorrel. It is not very productive so it is more of a curiosity than an important part of my diet. As well as being eaten the leaves can be dried and used to make a tea. There is even apparently a sorrel tree, Oxydendrum arboreum, which is a member of the heath family, but a whole tree of sorrel might be too much of a good thing.

I mostly use sorrel chopped into a salad, but its most traditional use is in sorrel soup, particularly in Eastern Europe, where it is sometimes known as green borscht. Here’s my favourite sorrel soup recipe.

Ingredients
oil
1 onion, 1 clove garlic, chopped
1 potato, cut up small
600 ml stock (1 pint)
1 handful sorrel leaves, chopped
optional: 1 egg, beaten

Fry the onion in the oil until soft, then add the garlic and the potato and fry for a couple minutes more before adding the stock. The stock can be whatever kind you like: chicken is traditional but I use vegetable. Bring to the boil and add the sorrel leaves, which will immediately lose their bright green colour and go much darker. Cook for around 10 minutes until the potatoes are soft, then blend and serve hot or cold.

The size of the handful of sorrel leaves depends on how sour you want it to be. One hundred grammes (4oz) or more will give give it a good bite; 50g (2 oz) will give a hint of sorrel that slowly grows on the back of your tongue as you work your way through a bowl, an effect that I quite enjoy.

For a twist, you can add a beaten egg at the end, cooking for a few more minutes, which gives the soup a lot of body. Serve with a hard-boiled egg or a dollop of sour cream (the mallow flower isn’t strictly necessary, but there were lots of them growing next to the sorrel patch).