How to Grow and Care for the Mustard Plant

Mustard is a hardy annual vegetable is grown for its leaves, also sold as mustard greens, or for its seeds to make mustard. What is commonly referred to as the mustard plant are in fact three different species: brown mustard (Brassica juncea), white mustard (Brassica alba), and black mustard (Brassica nigra). The plant grows about 3 feet tall with bright yellow pretty flowers, which are also edible. 

Mustard is not finicky and easy to grow, but because it’s a cool-weather crop, proper timing of the planting is important. Mustard is started from seed in the early spring or later summer. In warm climates, it can also be started in the fall for winter harvesting.

How to Plant Mustard

When to Plant

Mustard can be planted in the spring or in the fall. In the spring, you can plant it as soon as the soil temperature remains above 40 degrees F. Because mustard prefers cool weather, a fall harvest usually produces better quality. 

For fall plantings, it is recommended to select varieties that mature early. Plant the mustard in the late summer or, if you live more south, in September or October for a fall and winter harvest. To calculate your fall planting date, add 2 to 3 weeks to your average first frost date. Then count back 50 to 75 days (or the anticipated maturity date of the variety you are growing).

Select a Planting Site

Mustard needs a location in full sun with well-draining soil. Make sure to follow the rules of crop rotation and don’t plant it in the same spot where other members of the Brassica family were grown in the past two years or ideally even longer. 

Spacing, Depth, and Support

The space between the plants and the rows depends on the variety, and also on what you grow the plants for. Rows of mustard greens that are harvested regularly can be spaced as little as 12 inches apart whereas mustard with fully developed seed heads should be planted in rows 2 to 3 feet apart. 

When growing mustard for seed, staking the plants is recommended. 

Mustard Plant Care 

Mustard is easy to grow but it does not compete well with weeds, especially when the plants are still small. Closely spacing the plants (and thinning them as they grow) helps to control weeds. When removing weeds around the plants, cultivate the soil only so you don’t damage the roots. 

Light

Mustard should be grown in full sun. Partial shade is only acceptable when you grow mustard for baby greens, which should be protected from the strong sun as the weather turns hot. 

Soil

While mustard grows in most soils, a fertile, moist, well-draining, slightly acidic soil with a pH below 6.0 is best. 

Water

As a cool-season crop, mustard needs consistent but not excessive moisture. Give it at least 1 inch of water in the absence of rain. In dry soil conditions, leaf growth is slow, the leaves will be tough and have an off-flavor. 

Temperature and Humidity

Cool weather, even down to 32 degrees F, is not a problem for mustard but hot weather is. The plant does not do well in temperatures over 75 degrees F.

Fertilizer

Choose a fertilizer that is high in nitrogen, following label instructions for the amount. Scatter it around the seedings when they have reached 3 to 4 inches in height. 

Pollination

Although mustard is self-pollinating, pollination is nonetheless a consideration because pollinating insects can cross-pollinate the flowers of different varieties within a 2-mile radius. That means that if you want to save the seeds for next year’s planting, do not plant different varieties at the same time (and hopefully nobody in your neighborhood grows mustard either).

Types of Mustard Plants

The three common types of culinary mustard are: 

• White or yellow mustard (Brassica alba, other botanical name: Sinapsis alba). Zone 4-7. This is the mildest tasting of all mustards. Its seeds are used to make prepared mustard. It is not grown for its greens. 
• Brown mustard (Brassica juncea). Zone 2-11. This is the hottest mustard. The seeds are used for Dijon-type mustards, Chinese hot mustards, and curries. It is also grown for its greens and there are several cultivars. Popular ones include ‘Giant Red’, ‘Red Garnet’, and ‘Southern Giant’ with curled leaves. 
• Black mustard (Brassica nigra). Zone 6-9. The seeds are used for moderately spicy mustard and are also included in Dijon-style mustard. The seeds are also used in Southeast Asian cooking. It is not grown for its greens. 

Harvesting Mustard Greens and Seed

If you are growing mustard plants for their leaves, cut them while they are small, young, and tender and use them in salads. For sautéing or stewing, let the leaves grow to their full mature size but harvest them before a seed stalk forms.

Cut the large outside leaves at the base without damaging the growing point. Even if you don’t use the large leaves, remove them anyway to make room for the small, more tender inner leaves that will continue to grow, and you can cut them repeatedly. 

To harvest the seeds, watch the plants closely after the bloom to catch the point in time when the seed pods turn from green to brown but don’t open yet because otherwise, they will disperse the seeds all over your garden.

You can either cut off the branches with the mature seeds pods or remove the entire plants. Place an old sheet on the ground so you can easily gather any seeds and seed pods that fall off the plants.

Air-dry the pods on a tray lined with an old sheet or on a fine screen for about 2 weeks.

Alternatively, place them in paper bags and hang them in a warm, dry place. The seed pods are ready for further processing or storage when they are completely dry and crispy. 

How to Grow Mustard Plants in Pots

Mustard can be planted in pots, but that option is only suitable when growing them for the greens, as you need a substantial number of plants to produce seeds for mustard.

Plant the seeds in pots of at least 8 inches in diameter and filled with well-draining potting mix. Thin seedlings to 4 inches apart. 

Like all potted plants, mustard needs more frequent watering and fertilization than plants grown in the garden. 

Pruning

As an annual vegetable, mustard requires no pruning. 

How to Grow the Mustard Plant from Seed

Although you can start mustard seedlings indoors, direct seeding is the preferred and easiest method to start mustard plants.

Place the seeds 1 inch apart and ¼ to ½ inch deep in a prepared garden bed.

Keep the soil evenly moist at all times. At temperatures between 45 and 75 degrees, the seeds germinate in 4 to 14 days.

When seedlings are 3 to 4 inches tall, start thinning them out (they can be eaten) to 4 to 6 inches apart, and increase the space as the plants grow. Aim for 12 to 18 inches of space between large varieties and 6 to 10 inches between smaller, leaf-type varieties. 

Common Pests and Plant Diseases

Mustard is not affected by serious pest and disease problems. In humid weather, it can be susceptible to powdery mildew and white mold. Common insect problems include aphids, whiteflies, cabbage worms, cabbage loopers, slugs, and flea beetles. If these are a problem in your area, protect the plants with row covers. Adjusting the planting time can also help. For example, to avoid flea beetles, plant mustard in the fall when populations are much lower.