Growing Mustard at the Allotment

Growing mustard in the UK is a simple and enjoyable activity for children, amateur growers and more experienced growers alike. It also works well as a cover crop after harvesting sweetcorn and other summer vegetables.

Mustard plants belong to the Brassica family and can be grown for their spicy salad leaves, their seeds, or both. They are quick to germinate and easy to manage.

You can grow mustard for its flavour or as a useful companion plant. Unlike nitrogen-fixing plants like peas and beans, mustard acts as a nitrogen lifter and helps keep weeds under control, supporting the overall health of your plot. It can also be grown as an autumn green manure.

If you want to learn how to grow mustard, when to plant mustard or when to pick mustard, this guide covers everything you need to know.

Growing Mustard in Summary

Sowing Mustard

Sow before last frosts from early April
Sow in full sun or partial shade
Thin out seedlings if need be

Growing Mustard

Protect against slugs and snails
Water during dry spells
Quick to grow, and upto approximately 60cm high

Harvesting Mustard

Pick pods as they turn from green to brown befofe they are fully ripened
Dry out pods for 2 weeks
Pop the pods for the seeds and store

How to Grow Mustard

You can grow several types of mustard. Some are grown for their leaves, which are used in salads, while others are cultivated for their edible seeds. When growing mustard in the UK, you’ll mainly find 2 varieties:

Brown mustard (Brassica juncea): Varieties such as ‘Dragon’s tongue’, ‘Giant Red’ and ‘Golden Frills’ are grown for their mustard greens.
White mustard (Sinapis alba): This variant is primarily grown for making English mustard.

When to Plant Mustard

You can grow mustard as a successive crop because it is flexible, tolerant to varied weather conditions and has a short growing period. Plant in spring (April to May) if you want to use it for salad leaves. Overwintering varieties can be planted in a polytunnel from late summer to early autumn, between August and September.

The best time to sow mustard outdoors directly is early to mid-April, just before the last frosts.

If you want to grow mustard as microgreens, sow them indoors regularly in seed trays or containers.

Tips for Growing Mustard

You can scatter mustard seeds directly where you want them to grow, giving them a light covering of soil and water. Thin the seedlings later if required.
Mustard is a dense plant with plenty of leaves, so allow approximately 10 inches between each.
It can also be successfully grown in containers.
Mustard grows well in most soil types as long as the ground is not waterlogged.
Adding some well-rotted manure or sand can improve soil structure.
Mustard prefers full sun or partial shade and thrives during the cooler parts of spring and summer.
Water regularly in hot, dry spells.
Protect your mustard plants from slugs and snails, which often hide in the dense foliage.
You can grow mustard as a “catch crop”, planting it after harvesting summer crops. Before seeds start appearing (typically within 6 weeks), the plants can be dug into the soil to help revitalise it.

How to Harvest Mustard

Mustard can grow quite tall, producing yellow flowers and occasionally white ones, after which seed pods begin to form. The flowers typically appear within 4 to 6 weeks, while the plants reach full maturity in around 10 weeks.

Harvest the pods once they turn from green to light brown. Dry them for approximately a fortnight before opening them to collect the seeds. If left on the plant, the pods will likely self-seed throughout your plot. Store the harvested seeds in an airtight container to keep them fresh.

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