I first came across Diplotaxis tenuifolia at a seed swap on my allotments site. It was labeled ‘wild rocket’ so, thinking it was nothing more than a wild version of the familiar salad leaf (also known as rucola or arugula), I sowed a row and more or less forgot about it. When it grew, there was nothing to make me change my mind. Its attractive, lacy leaves looked like a finely-cut version of rocket and that distinctive peppery taste that you either love or hate (I love it) was there.
But then it did a very un-rocket-like thing. It kept on growing. And growing. The frustrating thing about ordinary rocket is that it just wants to flower and seed, so the period during which it can be bothered producing leaves is little more than a month. My new rocket flowered profusely with lemon-yellow crucifer flowers that the hoverflies clearly loved, but it also went on and on producing new leaves, eventually making a bushy, if floppy, plant about a foot high. Finally, I made some discreet inquiries into its parentage.
Wild rocket, it turns out, is just one of the names of D. tenuifolia, along with sand rocket, sand mustard, Lincoln weed and perennial wall rocket. These give a clue to its habitat. It likes a free-draining soil, be it sandy or rocky, and doesn’t need much in the way of water or nutrients. Ideally for my forest garden setup, it will also tolerate some light shade. It is also perennial, meaning a much longer period of leaf production than annual rocket. It is still growing in my garden in Aberdeen, despite several heavy frosts, and last year it went on until the first snows. It is also very early to come back into production once winter is over.
The taste of wall rocket is much like that of its annual cousin, but with a hint of cabbage and more of a kick. The leaves get stronger as they get older, but there is a continual production of fresh leaves, so I don’t find this matters much. You can cut the plant down to encourage a bigger flush of new leaves. If you have lots of older leaves, you can blanch them in boiling water for about 30 seconds which reduces the heat a bit. Cooking them for longer than this isn’t recommended as they lose their flavour entirely. My favourite uses are in salads, sprinkled on pizzas once they come out of the oven and as a topping for pasta sauces. You can also make soup with them in the same way as you make watercress soup.
The final surprise that wall rocket had for me came when I tried to move a couple of plants. They had deep, fleshy tap roots, which means that they probably act as dynamic accumulators in the garden ecosystem.