Szechuan Pepper, Zanthoxylum simulans

Our Szechuan Pepper bush, Zanthoxylum simulans, is producing fruit for the first time.

I first read about Szechuan Pepper ten years ago, when I bought Mark Diacono’s book “A Taste Of The Unexpected”  (note 1). I wasn’t able to source a plant for Grapes Hill Community Garden in 2011 but when we replaced the big raised bed in our front garden in autumn 2016 I had another look online and bought a small plant from Jurassic Plants. It had clearly been grown with love and care, and came with an A4 printed sheet of care instructions. I kept it in an unheated greenhouse and planted it out in early spring 2017. (In the UK, plants are available from other sources too, such as Burncoose Nurseries and Pennard Plants. Seeds are available from Chiltern Seeds.)

Two years later, the Szechuan Pepper is doing well and has reached about four feet (1.2 metres) high, with a similar spread. Without pruning, it could ultimately reach seven metres (23 feet) tall but I will intervene long before that – and, if space is really limited, it is apparently a good bonsai plant (note 2). It is very hardy and seems tolerant of drought and likes the sunny, south-facing spot where it is growing. (It will also grow in light dappled shade.)

Zanthoxylum simulans is a member of family Rutaceae, the Citrus family, along with well-known fruits such as Oranges, Lemons and Grapefruit. There are about 250 species of Zanthoxylum worldwide, trees or shrubs native to warm temperate and subtropical areas. Zanthoxylum simulans is native to eastern China and Taiwan. The genus Zanthoxylum is so-called because some species have yellow heartwood (Ancient Greek xanthos (yellow) and xylon (wood)).

So why am I growing Zanthoxylum simulans?

It is an interesting and quite attractive plant, with rather formidable spines on its stems and ash-like leaves, which turn an attractive reddish-yellow in autumn. The shape of the leaves gives the plant its alternative English names of Prickly Ash, Chinese Prickly-ash and Flatspine Prickly-ash.

The flowers appear in spring and are rather tiny – I missed them altogether this year but they are described as tiny, cup-shaped flowers in cymes 5 cm (2 inches) across. (Mark Diacono says that they resemble small elderflower florets.) By July or August the plant has clusters of small pinky-red fruits. These are ornamental, but also contain the plant’s finest and strangest secret.

Known as Szechuan peppercorns, each berry is about the size of a black peppercorn (an unrelated, tropical vine, Piper nigrum). The seed is black and is revealed when the berry splits open in the autumn. The seed itself is tasteless but its pink coating (the pericarp) gives a fizzing and numbing sensation in the mouth and on the tongue.

Szechuan (Sichuan) peppercorns are used to make Chinese five spice powder, along with star anise, fennel, clove, and cinnamon. The powder is readily available, but Mark Diacono gives a recipe for making your own in his book and 2010 Guardian article. The Spruce Eats website lists a number of recipes using the powder (including Bang Bang Chicken, Dan Dan Noodles and Szechuan Beef) and Mark Diacono suggests Five Spice Pork Rillettes. The Vegetarian Times website lists several vegetarian and vegan recipes that use five spice mix, such as Garlic Ginger Vegetable Stir-fry and Spicy Peanut Noodles. Other culinary uses include flavoured salt or as additives in beer or in flavoured oils.

The experience of tasting a Szechuan Pepper is described by Mark Diacono as “like all peppers… much more an experience than a flavour”. He separates out two contrasting elements of flavour: “ma” and “la”. First comes “ma”, a numbing pungency that sets the tongue and lips tingling, followed by “la”, a spicy heat, which is (slightly) similar to the heat from a chilli. In my own experience, the “ma” is much more obvious. It doesn’t last long, but it is strangely addictive. I often pick a single berry when I walk to the allotment, carefully suck the pericarp and discard the seed. Full fizzing numbness starts several yards down the road, but has worn off after two or three minutes.

The ingredient in Szechuan Pepper that causes the tingling numbness is the compound hydroxy-alpha-sanshool. Rather like the capsaicin in chillies, the chemical interacts with nerve cell receptors in the lips and mouth. In his book “On Food And Cooking: The Science And Lore Of The Kitchen“, the American author Harold McGee describes the chemical’s effects in the mouth:  “they produce a strange, tingling, buzzing, numbing sensation that is something like the effect of carbonated drinks or of a mild electric current (touching the terminals of a nine-volt battery to the tongue). Sanshools appear to act on several different kinds of nerve endings at once, induce sensitivity to touch and cold in nerves that are ordinarily nonsensitive, and so perhaps cause a kind of general neurological confusion.” (note 3).

The import of Szechuan peppercorns into the United States was banned in 1968 (along with all other citrus products) because Zanthoxylum plants act as hosts for a type of canker that attacks citrus trees. However, the ban was lifted in 2005 for peppercorns that had been heat-treated to kill off any potential pathogens, much to the relief of Chinese communities in particular.

My single Szechuan Pepper has set plenty of fruit by itself, but even more fruit can be set if you have more than one plant.

If you can’t get hold of Zanthoxylum simulans, Mark Diacono suggests Zanthoxylum schinifolium. (“I prefer its lighter touch – it’s more “ma” than “la”.“) UK suppliers include Van Den Berk Nurseries (who have some good photos and information on their website) and (for seeds) the Agroforestry Research Trust.

The wonderful Chelsea Physic Garden in London has a big specimen of the related North American species, the Toothache Tree (aka Common Prickly-ash)  Zanthoxylum americanum, “with spines and knobs along its trunk and branches – the small, round, fleshy fruits smell strongly of cloves when crushed“.

It is also worth rubbing the leaves of a Szechuan Pepper plant to release a heady hit of spice and citrus. In the words of Mark Diacono once more: “Like a tea break, it provides a perfect punctuation to the day, and is up there with popping fresh peas into your mouth as one of the finest kitchen-garden treats.”