Mustard plant: flowers, varieties, care & uses

Mustard is often grown in vast quantities in large fields, but it can also be very decorative and useful in our home gardens. Discover the different types of mustard available and how to care for mustard plants.

Mustard has a long history. It has been used for thousands of years as a spice and in the Middle Ages as a medicinal plant. Today it is becoming increasingly popular in home gardens. Read on for an overview of the different types of mustard plants and to find out how to grow mustard in your own garden as well as how to use mustard plant seeds.

Mustard plant: origin and properties

If you see fields full of bright yellow flowers in the autumn, there is a good chance that what you are seeing is a field of mustard flowers. White and brown mustard (Sinapis alba and Brassica juncea) are the two most common types of mustard grown in the UK. Black mustard (Brassica nigra) is rarely grown agriculturally because of the difficulty of mechanical harvesting. Botanically speaking, brown and black mustard are not “real” mustards at all, because neither plant belongs to the mustard genus (Sinapis).

The elegant yellow mustard flowers look remarkably similar to rapeseed. Both plants belong to the cruciferous family known as Brassicaceae, but differ in flowering time, odour, and use. If you sow mustard in May or start it on the windowsill from February onwards, it will bloom between June and September and can be used as a decorative flower.

Mustard is believed to originate from India, where cultivation remains were found during excavations that date back to around 1800 BC. On the European continent, mustard was first mentioned in a mustard paste recipe from ancient Rome from around 100 AD. This makes mustard, along with horseradish, the first hot spice in Europe — even older than pepper and chilli. In the Middle Ages, black mustard was purported to have healing and anti-inflammatory properties and was said to promote blood circulation and relieve pain.

But what do mustard plants look like? White mustard grows 30 to 70cm tall, brown mustard to 120cm and black mustard up to 200cm. A distinctive feature of this annual herb is its angular, top-branched stem from which the rough leaves grow. In addition, mustard plant leaves are divided into a petiole and an ovate leaf blade. The leaf edges are mostly smooth to slightly toothed. Mustard flowers have four petals and six stamens, and there is hardly any difference visually between the flowers of mustard and rapeseed. The main distinguishing feature is the flowering time. While rapeseed flowers bloom as early as spring, mustard plants do not flower until late summer to autumn.

Mustard flowers are hermaphroditic and can self-pollinate, so they do not need another plant as a pollen donor. Pollination occurs either by wind or by insects visiting the flowers. Mustard plants develop a deep root system, which makes them well-suited for loosening soils, as an intercrop, or as a green manure. Mustard seeds are formed in pods and are about the size of peas. You can use them whole, grind them into powder or use them to make the mustard sauce most of us have in our pantry.

Types of mustard plants

To help you distinguish between white, brown and black mustard, here is an overview of these three types of mustard:

• White mustard (Sinapis alba): also called yellow mustard because of its intense yellow flowers. It forms 4 to 8 seeds per pod, and the seeds are white to light yellow with a mild flavour.

• Brown mustard (Brassica juncea): commonly referred to as Indian mustard, Chinese mustard, or leaf mustard. Brown mustard produces 6 to 15 seeds per pod, which are dark to light brown. Mustard oil is still commonly used in Asia, but here it has been replaced by rapeseed oil, as mustard has a comparatively low yield. Brown mustard has a sharp flavour and is more commonly used in Dijon mustard. ‘Rouge Métis’ is an interesting variety that has a slit, red-purple leaf, making it particularly decorative in salad. And the variety ‘Southern Giant Curled’, otherwise known as curly mustard, is also highly recommended. It forms large leaves that can be used in salad, on bread or cooked like spinach.

• Black mustard (Brassica nigra): this type of mustard produces 4 to 10 seeds per pod, which are dark brown or grey to black. They have a conspicuous black stem, usually hairy at the bottom, which turns blue towards the top. Black mustard is not grown commercially because the pods are very close to the stem and therefore cannot be harvested well by machine. It has a sharp flavour.

Caring for mustard in the garden

When planting mustard plants, opt for a sunny or at least semi-shaded location. They prefer a humus-rich, limey soil. It is possible to grow mustard next to almost all other vegetables, except other cruciferous vegetables such as cauliflower (Brassica oleracea var. botrytis) or broccoli (Brassica oleracea var. italica). Hold off growing any plants from the Brassicaceae family again in the same spot for at least 4 years to avoid the spread of plant diseases.

Mustard is a very undemanding plant during the growing period. If grown in a location with plenty of nutrients, watering regularly is enough. If you are using mustard as an intercrop or to improve soil structure, this is usually done on poorer sites. In this case, fertilise your mustard plants to provide them with additional nutrients. This allows the plant to develop fully and improve the soil. Additional fertilisation of mustard on a poor site ensures a healthier growth, so the plant can store the necessary nutrients and release them when it rots on the compost or directly on the bed. Due to the good growth of the mustard plants, carbon is fixed and usable as humus after rotting.

Suitable fertilisers include our primarily organic Plantura All Purpose Plant Food. This not only provides the plant with ideal nutrients, but itself supports soil organisms. Since mustard is an annual plant, it dies in the autumn and is therefore not hardy. If you do not harvest the mature mustard plant seeds, your plant will naturally sprout again the following year.

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Harvesting mustard

Just 3 weeks after germination, the first leaves can be harvested. They taste delicious when added to a fresh salad, and in Indian cuisine mustard herb is often used to cook spinach-like vegetables. If the leaves are older, they become bitter and do not taste as good. As soon as the mustard begins to bloom, stop harvesting the leaves entirely. This allows the plant to put all its energy into flower and pod formation rather than developing new leaves.

The mustard pods are ready for harvesting once they have dried. This is usually around September or October. If the pods rattle when shaken, they are dry enough. Simply remove the pods from the plant by hand, open them up and extract the seeds. For a large crop, place the pods in a bag and tap them with your hand or a rolling pin to loosen the mustard seeds. This makes it easier to collect them.

Storing and preserving mustard

The harvested mustard seeds can then be dried. Just put them on a newspaper and leave at room temperature in a well-ventilated room for about 4 weeks. If you put the newspaper with the mustard seeds on the heater, they will dry even faster. Store the mustard seeds in a dark, dry place or grind them into mustard flour. You can use them when pickling vegetables such as gherkins or as a seasoning for meat and vegetables. As an alternative to drying, the mustard seeds can also be processed directly into mustard sauce.

Mustard plant benefits

Since the Middle Ages, mustard has been considered a medicinal plant with many health benefits. The different varieties consist of approximately 20 to 30% mustard oil, which contains many healthy, unsaturated fatty acids. Mustard also contains a high percentage of protein (about 28%). The glycosides found in mustard are responsible for its pungency. White, brown and black mustard all contain different types of glycosides. Mustard’s pungent taste is only brought out once the glycosides are crushed and react with an enzyme. That is why when you chew a mustard seed it tastes sweet and nutty at first, and becomes spicy after a while.

Common mustard pests

Mustard is a very hardy plant and is hardly susceptible to any pests. However, just like other cruciferous vegetables, flea beetles can become problematic during periods of drought. As a preventive measure, remove weeds early, water the plants regularly and help to keep the soil permanently moist by applying a layer of mulch.

You can control white flies with beneficial insects. Having a bug hotel and planting a flower meadow in your garden will aid in attracting the right beneficial insects. This will not only benefit your mustard plants, but your whole garden.