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Grow Mustard Seed In Your Garden

Mustard greens are one of those fail-safe vegetables that anyone can cultivate and produce great harvests. I always grow way more than I need, so this year I’ve decided to allow some plants to mature to grow mustard seed. Yes, you read that correctly!  Mustard greens produce mustard seeds as well as other greens for your next stir fry! 

Mustard is a fabulously versatile crop.  Mustard grown for seed is usually allowed to bolt, but before it bolts, it can be grown as mustard greens as the entire plant is edible. It can also be grown as mustard microgreens. The greens are a cool-weather peppery, slightly bitter cut-and-come-again salad leaf, rich in antioxidants and packed full of vitamins. It can also be grown as green manure or cover crop, used to suppress weed growth, and acts as a biofumigant when dug into the soil.

Finally, when mustard plants flower they produce mustard seeds, the key ingredient in mustard sauce, giving it that signature heat and spicy flavor.  Seeds can also be used to liven up potato, vegetable, and meat dishes as a powdered spice or cracked lightly and added to rubs, marinades, and curries.  I’m especially looking forward to trying homemade mustard sauce recipes that include ingredients like beer, port, honey, herbs, and stout!

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Quick Care Guide

Grow mustard seed
It’s easy to grow mustard seed in the garden. Source: Beth Sargent
Common Name(s)Mustard
Scientific NameBrassica (B juncea, B nigra and B alba)
Days to Harvest85-95 days
LightFull sun to part shade
WaterRegular consistent watering
SoilFertile, well-draining soil
FertilizerNitrogen in spring, balanced general fertilizer before flowering
PestsAphids, flea beetles
DiseasesPowdery mildew, downy mildew

All About Mustard Plant

Mustard flowers
Mustard flowers are really quite beautiful. Source: flyingkiwigirl

Mustard is the common name for a wide group of annual plants in the cabbage family, Brassicaceae, grown for their leaves and seeds.  There are several species of mustard producing different colors and flavor of seed such as Brassica juncea, Brassica nigra, and Brassica alba.  Mustard is a cool-weather crop believed to be adapted from wild radish and turnip with its origins in western Asia and Europe.

Leaves and flowers vary in appearance depending on the species or variety.  Leaf mustard can be deeply lobed, frilly, or oval in shape. It can be dark to light green, red, or purple in color, making them an attractive addition to any salad bowl.  Mustard plants tend to have yellow flowers but can sometimes be creamy white.  Flowers are produced on tall spikes ranging from 12 to 36 inches (30 – 90cms) in length.  Long thin green seed pods (approx. 1 inch/2.5 cm long) develop after flowering, slowly turning light brown as they mature and ripen.  Pods will burst when seeds are ready making for a slightly invasive plant if left unmanaged.

Mustard has a vigorous growth cycle.  Seeds germinate between 5 -10 days and grow quickly forming a rosette of basal leaves.  As plants mature a multi-branched flowering spike grows from the base producing pods when flowers are spent.  The time taken from sowing seed to harvesting seed is around 90 days.

All parts of the mustard plant are edible.  The leaves and flowers are used in salads and stir-fries and the root can be used as a root vegetable, roasted, boiled, or chipped.  The seeds can be used to flavor ferments, marinades, meat, vegetable, and fish dishes as well as used to make iconic mustard sauces.  

Mustard is also grown as green manure dug into the soil in spring adding organic matter, improving soil structure and moisture retention.  As a cover crop mustard suppresses weed development and protects bare soil from the elements. As a member of the cabbage family, mustard should follow the rotation cycle of other brassicas such as cauliflower, broccoli, and kale.

Types of Mustard Seed

Mustard is the second most used spice in the United States after peppercorns and there are over 40 mustard varieties to try.  Here are a few of the main types of mustard seeds available.

Brassica alba: Yellow/white mustard seeds. This is the mustard mainly used for moderately spicy mustards. It has the mildest flavor and the largest seeds. This is what’s used to make a traditional “Ball Park” mustard style of yellow mustard, as both the yellow seeds and white seeds can be combined to produce that brilliant color.

Brassica juncea: Brown mustard seeds have a darker seed coat and are used to make dijon style mustard.  It is also mixed with yellow mustard seeds to create English mustard or spicy brown mustards.  Other common names for these brown seeds include Chinese mustard or Indian mustard. B. juncea is used on its own to produce Chinese hot mustards but is also called true dijon mustard as its zingy flavor mellows when blended with wine. Red giant mustard is a Brassica juncea variety that produces purple leaves perfect as Asian greens in cooking. Another popular variety is Southern Giant.

Brassica nigra: Black mustard seeds which are smaller than other types.  The black seeds have the strongest flavor of all mustard seed types. Occasionally black mustard seeds will be blended with yellow mustard instead of brown ones to make a spicy mustard type.

Planting Mustard

Black mustard seed
Black mustard seed can range from this shade of brown all the way through truly black. Source: Will Humes

Sow mustard seeds indoors in early spring, 4 – 6 weeks before the average last frost date, ½ inch deep (1cm) in cell trays filled with seed starting mix. If desired, select an organic mustard seed variety if you’d like to produce an organic mustard plant.  Seeds should germinate within 5–10 days.  Gently harden off transplants and mustard seedlings for at least a week and plant outside after the last frost. This builds up a tolerance to outside conditions, reducing the risk of stress that causes plants to go to seed.  When plants go to seed they produce less harvest with a milder flavor. 

Plants grown for seed require more space than if growing mustard greens. Space plants 10 inches apart (24cm) and 12 inches between rows.  Sow seeds direct after the last frost into prepared beds and thin seedlings to 10 inches apart (24cm).  More space means less competition for water and nutrients required for seed production. 

Choose a bright sunny spot to grow your mustard with fertile, well-drained soil.  In warmer areas provide a bit of shade from the midday sun.  Mustard will grow well in a large heavy container with some support when they grow quite tall.  The benefit of growing in containers is that seeds can be started off indoors and moved outside after the last frost to continue to grow in cool temperatures avoiding the increasing heat of the greenhouse.

Care

Mustard plants
Mustard fields look like yellow-capped waves on a green sea. Source: flyingkiwigirl

Growing mustard seed is straightforward. However, there are a few care tips you should follow to get the most from your crop.

Sun and Temperature

Mustard likes to grow in full sun to partial shade.  In hotter climates you may need to use shade covers to keep plants cool and prevent bolting.  6 hours of sunlight per day is sufficient to grow mustard in USDA zones 2 – 11. 

As a cool-season plant the ideal growing temperature range is between 50–75ºF (10-23ºC) although plants may show signs of wilt or a tendency to bolt and grow mustard seeds at the higher end of this scale.  Mustard can tolerate a light frost but will be killed by prolonged freezing temperatures.  

Water and Humidity

Mustard is not drought tolerant, so regular, consistent watering will reduce plant stress and the risk of bolting.  Watering requirements are dependent on soil type and local temperatures. As a general rule, aim to water when the top few centimeters of soil are dry.  Periods of drought or high heat may affect the flavor of both leaves and seeds. Container-grown plants will also require regular watering to keep plants in optimum condition.  Use timed soaker hoses, a watering can, or garden hoses in the morning or in the evening if plants show signs of wilt in warm weather. 

Soil

Grow mustard in fertile, loamy, well-drained soil. Plants will tolerate poor-quality soil but may require supplementary feeding. Organic mulches are perfect for boosting soil fertility and will help maintain moisture and soil temperatures. Soil pH from slightly acidic to slightly alkaline is adequate to plant mustard.

Fertilizing

Plants grown in amended soil will not need fertilizer until the first flowering stems appear. At this point feed plants with a well-balanced fertilizer to boost flower and seed production.  On poorer soils feed plants with a nitrogen-rich liquid fertilizer in spring to encourage leaf growth followed by a balanced fertilizer once plants are established.  

Harvesting and Storing

Yellow mustard seed
Yellow mustard seed is the most widely-consumed in the United States. Source: Will Humes

The key to harvesting lots of good quality mustard is knowing exactly when to harvest and how to dry your seeds ready for storing. 

Harvesting

You can harvest leaves for fresh eating regularly throughout the plant’s early life, but when the weather starts to get too warm, the plant will bolt and start to grow mustard seeds. At that point, the leaves often become bitter and less palatable, so be sure to visit your vegetable garden regularly for young greens during the right season.

Harvest seeds before they are fully ripe.  Leave it too late, and the pods will burst and the seeds will be lost (or at least self-sown into your garden to create volunteer plants next year!).  Seed pods ripen from green to light brown, so watch closely and choose the right time for your crop. Another indication that plants are almost ready to harvest is when the leaves at the base of the plant turn yellow.

To harvest simply cut stems and tie them together in bunches.  Hang upside down to dry somewhere cool and well ventilated making sure to tie a paper bag over the seed heads to catch seeds as they ripen and fall.  Alternatively, stems can be laid flat on a fine mesh or sheet to let the seed pods dry.

Once the pods are completely dry it’s time to shake out those seeds. Pods should feel crispy when rolled in your hands releasing the seeds easily. Hold the bunches in a bag or over a large tub and thresh the seeds from the pods. Seeds may have little bits of chaff from the pod still attached.  To remove this, slowly pour the seeds from one bowl to another in front of a fan and the little bits will winnow away leaving you with clean, dry fresh seed. You may need to repeat this process a few times.

Storing

Fresh mustard leaf should be used quickly for its best flavor but can be stored in a bag in the crisper drawer of the refrigerator for a day or two. 

Slow drying the seed at cool temperature retains the best mustard flavor. If possible, air-dry your mustard seed in a cool, dark, but well-ventilated area. A dehydrator set on an air-only cycle with no heat is another excellent option.

Store dried whole mustard seeds in an airtight container for up to 18 months. Ground mustard seed loses its flavor quicker than whole seed so hold off on grinding until just before you need to use it. 

Troubleshooting

Mustard growing habit
Mustard leaves and newly-budding flowers. Source: RahelSharon

There are a few growing problems, pests, and diseases to look out for when growing mustard, but nothing that isn’t easy to handle.

Growing Problems

Plant stress is the main problem when growing mustard seeds. Stress causes plants to go to seed reducing the quantity and quality of the harvest.  Types of stress include high temperatures, an unexpected cold spell, inconsistent watering, or lack of nutrients.  To avoid bolting try and grow your plants at the right time of year for where you live and always keep the soil slightly moist but not wet. Amend poor soils with rich organic matter before planting or supplement with suitable fertilizer.

Mustard plants grown for seed can grow to 3ft (90cm) making them susceptible to wind damage.  Provide stakes or other plant supports as soon as flower heads become tall and top-heavy. 

Pests

Young mustard leaves are often attacked by aphids (Aphidoidea), small and sticky, yellow, green, black, red, or white pests that feed on the sap of new growth. Companion planting with marigolds or calendula will help deter aphids and encourage beneficial insects into the garden to feed on them.   Alternatively, spray with an organic insecticidal soap or neem oil.  Squishing aphids with fingers or a quick blast of water can also help to reduce numbers. 

Mustard leaves can be attacked by flea beetles which chew tiny holes in leaves making them unsightly and will affect the health and viability of the whole plant.  The best form of defense is to use floating row covers to prevent the beetles from getting to the leaves.  Mustard should also follow the rotation cycle of other crops in the brassica family. Spraying neem oil may also help.

Diseases

Mustard leaves are susceptible to powdery mildew if plants are grown too close together or are overshadowed.  It grows as thick dust on leaves, inhibiting photosynthesis and hindering growth.  Downy mildew is another disease affecting mustard causing white spots on the upper and underside of leaves. Both diseases seriously affect the health of plants and can result in reinfections in subsequent years. To avoid these diseases maintain good garden hygiene, remove infected foliage as soon as possible, and rotate crops every year.  Provide adequate sunlight and good air circulation and treat affected plants with an organic fungicide such as sulfur or potassium bicarbonate.

Frequently Asked Questions

Q: Can I grow my own mustard seed?

A:  Absolutely! Mustard plants are easy to grow and can be grown for their edible leaves, seeds, root, and flowers.

Q: How long does it take to grow mustard from seed?

A:  Depending on the variety of mustard seed you sow, seeds can be harvested in 85-95 days.

Q: Can I grow mustard greens from mustard seeds?

A:  Yes! Save your mustard seeds to grow mustard spicy greens the following growing season.


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