Tropaeolum majus (Nasturtium, Indian Cress or Monks' Cress in English, Oost Indische kers in my native Dutch) is a versatile plant. Al parts can be eaten. The taste is freshly sharp, you can compare it with sharp reddish. The young leaves and especially the flowers make any salad a feast. The plant needs very little to grow. It can become huge with large watery shoots flowering everywhere and reaches it top in September. As soon as the first frost arrives it turns into snot. Once seeded it returns every year from the seeds of the year before. It is very easy to control by pulling them out or hoeing, so no worries there. It is excellent to grow against e.g. a fence or on a compost heap you want to hide. Although different varieties exist it is usually sold in a mix. You can pre-seed in the windowsill or greenhouse early in the season and plant them out when no more frost is expected.
The (young) seeds make superb "capers" who have a slightly fresh sharp taste, much like the leaves and flowers. You can used them in salads, pasta sauces and what not. I will tell you how to make them, it is very easy and rewarding.
Step 1: Pick the Seeds and Prepare
Once the plant is big enough to flower it will also produce seeds. The seeds are usually growing in clusters of three. Pick young seeds; the older ones can be slightly woody and not nice to eat. Test this by using your mouth: eat.
Once picked wash them and get rid of all things not wanted: stems, slugs, you name it. Make a brine of 75 gram salt per liter, put the seeds in and put the brine away in a dark and cool place like the top shelf of your fridge. You can use more salt; you can even use dry salt, pour it over the seeds and put them away; the result is similar. Leave them for 24 hours and make sure to cover them with cling film: the curing will produce a sulphur-like smell.
Step 2: Making the Capers
Rinse the cured seeds under a running tap. No worries: the smell will be gone quickly. Sterilise the jars you want to use by boiling them in water; do not forget the lids. Everything needs to be very clean; similar to making jam or chutney. Take a pan and make a sweet-sour mix of vinegar, sugar and your favorite herbs like mustard seed, garlic, small peppers etc. Bring to a slow boil and let boil for 10 minutes. In the meanwhile you can fill the jars with the seeds. Leave a small gap at the top so that the seeds will be totally covered in the sweet-sour liquid. Pour the hot vinegar/sugar/herb mix in the jars so that the seeds are completely submerged. Put the lid on and leave to cure for 4-6 weeks. The capers will be edible for many months provided you used sterile jars and lids.