The Blackthorn, or Sloe, Prunus spinosa, is one of my favourite wild shrubs. The plant produces masses of pretty white blossom in early spring and sloes, a key ingredient in Sloe Gin, in autumn.

Sloes, late October 2016

In a week’s time I am going along to a gin tasting organised by No Fear Gardening, a new Norwich-based urban gardening club. My role is to talk about some of the ingredients used to flavour gin, including sloes. So I thought I could combine some homework with another post on my blog.

Blackthorn, Prunus spinosa, is in the Rosaceae, the Rose family. The genus Prunus can be split into six subgenera and three of these include several important fruit trees. Subgenus Amygdalus contains Almonds (Prunus dulcis) and Peaches (Prunus persica); subgenus Cerasus contains Cherries (Prunus avium and Prunus cerasus ) and subgenus Prunus includes Blackthorn and domesticated Plum trees (Prunus domestica). Blackthorn is believed to be one of the parents of the domesticated Plum, P. domestica, the other being the Cherry Plum, Prunus cerasifera.

The genus also contains the poisonous European Cherry Laurel (Prunus laurocerasus – subgenus Laurocerasus), the North American Sand Cherry (Prunus pumila – subgenus Lithocerasus) and European Bird Cherry (Prunus padus – subgenus Padus).

The sub-genera are distinguished by characteristics such as the arrangement of axillary buds and flowers, and the shape of the fruit.

Blackthorn grows in much of the British Isles, in open woodlands, hedgerows, as scrub on commons and rough ground and on screes and cliff-slopes. Although it normally grows as a shrub, it will grow as tall as 2.5 to 4 metres and will sometimes form a small tree (to ten metres tall).

When it is given the chance Blackthorn will spread sideways and outwards by suckers and a bush can be as wide as it is tall and often much wider. Indeed, I’ve spent many days keeping Blackthorn in check where it borders grasslands such as Alderford Common near Norwich. Without any maintenance these places would become solid thickets of Blackthorn. As well as providing a day of fresh air and exercise, clearance work in the autumn would often provide a good haul of sloes from the cut branches.

After a long, dark winter, Blackthorn blossom in the hedgerows is very welcome. Here in Norfolk, Blackthorn usually blossoms in March or April but the exact time varies depending on how warm a spring we have. Spring weather is very variable and a cold spell will often coincide with the onset of Blackthorn blossom, giving rise to the phrase “Blackthorn winter“. Cherry Plum (Prunus cerasifera) flowers even earlier than Blackthorn, with equally spectacular flowers.

Blackthorn in blossom

Blackthorn’s specific name spinosa refers to its sharp spines (which Cherry Plum lacks). These are very sharp and my bike tyres have suffered a number of punctures from Blackthorn spines, when hedges have been flail-mown and cuttings have been scattered on the road. The spines, which can reach over two inches (five centimetres) long, are also a hazard for anyone picking sloes or cutting Blackthorn scrub or hedges and they can easily penetrate leather gloves and even tractor tyres. It is quite common for part of a spine to break off after it has penetrated the skin and this can lead to inflammation, which can be serious. J. J. Kelly documented a number of cases in the 1966 paper “Blackthorn Inflammation” (on the Bone and Joint website) and other examples are given by H. Sharma and A. D. Meredith in a 2004 paper. The Netmums website gives some advice for children injured by Blackthorn.

Kneeling on a Blackthorn spine is a particularly bad idea (but is easy to do). A Blackthorn spine lodged in a joint can lead to a severe inflammation known as Plant Thorn Arthritis, Plant Thorn Synovitis or Thorn Arthritis. (Blackthorn isn’t the only species that can cause this.)

On a more cheery note, Blackthorn is an important plant for wildlife. Its flowers provide nectar for insects that emerge early in the spring, such as Small Tortoiseshell, Peacock and Brimstone butterflies, bees and hoverflies. The spines help to protect birds which nest in the branches and Blackthorn thickets can provide good habitat for Nightingales. In many parts of Europe, Shrikes (such as the Great Grey Shrike, Lanius excubitor), nest in Blackthorn bushes and impale a larder of food items on the thorns, which gives rise to their alternative name, the Butcher Bird.

Blackthorn is the food plant of the Brown Hairstreak and Black Hairstreak butterflies. Both species are quite restricted in range in the British Isles and the Black Hairstreak in particular prefers dense stands of mature blackthorn. A number of moth caterpillars also feed on Blackthorn. The Clouded Silver (Lomographa temerata), Green-brindled Crescent (Allophyes oxyacanthae) and Dark Dagger (Acronicta tridens) will also feed on other shrubs, such as Hawthorn, but the Sloe Carpet (Aleucis distinctata) is restricted to Blackthorn.

Blackthorn is easy to grow, though it is susceptible to Silver Leaf Disease, caused by the fungus Chondrostereum purpureum. (See my post “Winter Fungi” from 2012 for pictures.)  In the countryside Blackthorn is normally cut in the winter, but where Silver Leaf is a problem, you should only prune in dry spells in summer. (This is usually advised for Prunus fruit trees, such as Plums, Cherries, Almonds and Peaches.) If you do grow Blackthorn, give it enough room to spread or be prepared to cut back its suckers.

You have to be brave to eat a raw sloe, the Blackthorn’s fruit, and if you do you will probably do it only once. Sloes are very astringent, though frost can reduce the astringency and the Plants for a Future website says “some people find they can enjoy it raw“. (Avoid the stones, as they may contain cyanide glycosides.) The leaves can be used as a tea subsitute and the flowers are edible. There are also several medicinal uses for the plant.

Blackthorn wood is very hard and is used for making walking sticks and clubs, such as the Irish shillelagh.

The best use of sloes is for making jellies, syrups, conserves or flavoured alcoholic drinks. Sloe Vodka is quite good but the best is Sloe Gin. This is good to drink after just three months, but improves with age and becomes smoother and richer the longer it is stored. To make sloe gin, put pricked, bashed or frozen sloes in a large jar or demijohn and add sugar and gin (a cheap brand will do). There are numerous recipes, including these by River Cottage’s John Wright and on the BBC Food website and Very Berry Handmade website.

There are some great photographs of Blackthorn on the internet, such as on the Sulgrave Village and Wildscreen Arkive websites.