At this time of year, nasturtiums (Tropaeolum majus) are making a splash everywhere, in flower beds, in hanging baskets, in the forest garden – and in the wok and saucepan. Many people will know nasturtiums for their brightly coloured, peppery tasting flowers, but there is a lot more to their culinary use than that.

All parts of the nasturtium – leaves, flowers and seeds – contain the aromatic oil that makes them taste similar to watercress, and all parts can be used in recipes that exploit this flavour. The flowers look spectacular in a salad or as a garnish and the leaves give an interesting twist to pesto. For me though, the biggest attraction is that all this colour and spice mask a less showy but equally useful side to nasturtium, as a very well flavoured green vegetable.

If you cook nasturtium greens, you will be left in no doubt that the aromatic oils are being driven off, as the heady smell fills the kitchen. The surprise is what is left at the end: neither the cress flavour of the raw vegetable nor the bland taste that might be expected, but another taste entirely, distinctive and very pleasant. One way to enjoy this is as a pot herb or spinach. Fry a small onion and some garlic in a pan until soft, then throw in a good quantity of washed nasturtium leaves and a little extra water. Put the lid on and cook for a few minutes. You’ll smell the oil being driven off – once that is over the leaves are ready. The result not only has a nice flavour but also a good texture: soft and buttery. This is very nice as a side dish in its own right, or you could substitute nasturtium leaves for spinach in more complex dishes or mix them together with other leaves.

Another way to use nasturtium is to harvest the soft growing tips, nipping off about 10 centimetres of growth, and use them in a stir fry. I add them near the end: they don’t need a lot of cooking and the ideal is if they keep a little of their cress flavour but not too much.

Nasturtiums are prolific seeders, and this gives another great product: the pickled green seeds. These are often described as caper substitutes, but to my taste they are on a par with capers. Used in similar ways but with a different taste, I’m happy to have both available. There are great preparation instructions on Garden Betty’s blog.

Nasturtiums like a well-drained soil, preferably in full sun. Growing guides tend to say that they do best in poor soil, but it is more accurate to say that they flower best in poor soil. They will grow quite happily in a rich soil, with lots of leaf growth. They are quite rampant and may smother plants that are too close, so give them a bit of space or plant them next to a taller plant that they can scramble up without inconveniencing too much. In my forest garden I have them planted next to some raspberries and also able to cascade over a low wall. The space next to them has wild garlic, which is well over before the nasturtiums really get going. Nasturtiums are annual but they produce lots of seed and often self seed; however, it’s still a good idea to save some seed over the winter so you can plant them where you want them. They can vary in vigour, flavour and size and the tips of some plants are a bit woody, so seed saving gives you a chance to propagate from your best plants.