Whether the weather is blazing hot, dry enough to turn your boots to dust, flooding and muddy or knee deep in snow, there is one “green” that just keeps growing: mustard. Mustard greens are the standby crop in southern USA. In parts of China they’re stirfried, with sauces ranging from savoury to spicy, or added to soup. They aren’t just “green”, either. One of the hardiest forms is a lovely deep purple-red. Plant the seeds in spring, or any warm time of the year, and within three weeks you’ll have young leaves ready to pick.

The young leaves are the best ones to eat in summer. Old ones can be too spicy and a bit fibrous and tough. Sometimes, too, that heat and spiciness is exactly what you need, especially if you’re cooking them with something fatty or smoky.

Mustard seeds can be sprouted to make “mini greens” for salads. They taste peppery but good. Children can sprinkle mustard seeds on damp cotton wool and watch them shoot, then chop these miniature greens for salads. Mustard greens go to seed the spring after they’ve been sown. The flowers are tall — about 1.5 metres high — and bright yellow, stunning with the purple leaves. Once the flowers have died back the seeds set, and those seeds are what mustard is made of.

Mustard has mostly been used simply because it tastes so good, not in large doses but to give spice and accentuate other flavours. These days, it’s spread over hot dogs, used with discretion in salad dressings, added to cream for sauces or served with cold meats.

The potted mustard we know today is relatively recent. Mustard was originally made into mustard balls — the ground seeds mixed with vinegar, honey and cinnamon and rolled into balls. Potted mustard, mixed with wine or vinegar for added sharpness, and also to preserve it, became popular in the middle ages.

Mustard powder — ground mustard seeds with stabilisers and sometimes other flavourings such as turmeric added — wasn't sold till the 18th century.

There are three main types of mustard grown to make potted mustard: Black mustard (Brassica nigra) grows to 1.5 metres, with bright yellow flowers, pungent leaves and black seeds. Brown mustard (B juncea) is a slightly smaller plant with brown seeds, as is white or yellow mustard, (B hirta or Sinapsis alba), which has slightly furry leaves, slightly furry pods and paler seeds. All have green leaves — the red-leafed variety is a “black mustard” and its seeds can also be used to make mustard. The leaves of all the mustards are edible and hardy, too.

Mustard’s true taste only comes after it is crushed and mixed with water, wine or vinegar and the two active ingredients of mustard, sinigrin and myrosin, come into contact. Mustard needs about half an hour to develop its full flavour, whether in a sauce or a relish. After a day or two the fragrance begins to fade unless in a sealed container and with an acid added. Mustard can be made at home without the vinegar needed to stop the mustard going stale, though most people now assume that mustard must have an acid, vinegary taste.

English mustard is usually made from white mustard seeds and its yellow colour comes from turmeric. European mustards are more often made from black or brown mustard seeds. Whole mustard seeds are added to pickles and sauerkraut and other relishes but, though they give flavour, they don’t give the same fragrance as when crushed. “Hot” mustards have had chilli or hot paprika added.

Mustard is also an excellent green manure crop. It may repel a number of harmful nematode species and possibly other soil-inhabiting pests (it was traditionally grown in old hen runs to lessen the worm burden in the soil). Mustard will tolerate soil with a lot of bird manure and will thrive where other plants might be burnt off. It can thus be grown in newly manured ground to “soak up” surplus nitrogen, which can be returned to the soil in a gentler form when the mustard is slashed.

Mustard for green manure should be slashed when it is about knee high, otherwise it takes a long time to rot down. Mustard that has gone to seed takes even longer to break down.

Basic homemade mustard

Experiment with your own herbs and with different vinegars and sweeteners. The seeds can either be crushed in a blender or cracked with a mortar and pestle or with the back of a spoon.

• 90g mustard seeds, ground or cracked
• 60ml vinegar (white wine vinegar, red wine vinegar, tarragon vinegar, cider vinegar, or even a good red wine, sherry, brandy, whisky or a mixture of vinegar and lime or lemon juice)
• 3 tbsp fresh herbs, finely chopped (tarragon, basil, rosemary, oregano, lemon thyme) if you are going to use the mustard soon, or dried herbs if you’re not going to use it within 48 hours. There is a risk the fresh ones may make the mustard “go off” and become toxic. Mustards with fresh herbs or garlic need to be kept in the fridge.

Blend all ingredients together, either in the blender or with a mortar and pestle. You can make a smooth blend or leave it slightly chunky or add more mustard seeds after blending to make a grainy mustard. Spoon into clean jars, seal and leave in a cool place, such as the fridge or larder, for two to three weeks to mature. Reseal and keep in the fridge after opening. Homemade mustard, made with dried ingredients, should keep for several months.