Top of The Crops - Mustard

Growing Mustard In A Polytunnel

Mustard is a perfect crop for children or beginner gardeners as it is so easy and quick to grow but can also be useful for the most experienced of gardeners. 

Sow certain types of mustard leaves for salad throughout the summer and into autumn in your polytunnel and you can be harvesting cut and come again leaves within only a few weeks. Growing mustard for seeds, and growing mustard as a green manure, are also options for polytunnel growers. 

Key Information

Mustard, a member of the Brassica plant family, shares close ties with common cabbage family members. With a plethora of varieties, some are cultivated for their leaves while others for their seeds.

Among those grown for their leaves, numerous cultivars exist, showcasing a diverse array of appearances and flavours, ranging from mild and sweet to intensely peppery and spicy. When selecting a cultivar, it's important to match it with your personal preferences and intended culinary uses.

While most mustard leaves belong to the Brassica juncea species, leaves from other mustard varieties are also edible. Sinapsis alba, commonly chosen for green manure, stands out, primarily grown for its seeds when not serving as a soil conditioner (though its leaves are also edible).

What You Will Need to Grow Mustard

To grow mustard you will need:

  • Mustard seeds (of the right variety of the yield that you require/ desire).

  • A suitable growing location that is reasonably sunny, with fertile, moist yet free-draining soil. 

  • Facility to water your crop. 

  • Basic gardening tools for sowing/planting/ weeding etc...

  • Organic matter for mulch/ soil health. 

How to Grow Mustard from Seeds

If you are interested in growing mustard then the first thing to think about is which type. There are many different types of mustard that are perfect for growing in a polytunnel. Which mustard or mustards you will choose will depend on what you want from your crop. 

Choosing Mustard Plants

Various mustards are grown as a fast-growing and hardy salad crop – one of the easiest things to grow in your polytunnel and useful over the colder months and for filling the 'hungry gap' in the spring. 

Other mustards are grown for their seeds, which are ground for use in the traditional condiment.

Still other mustards are used as a 'green manure' – sown with other brassicas in crop rotation and dug into the ground to add nutrients and replenish the soil.

Over winter, there are many type of mustard that will cope with the temperatures – just add extra protection if you live in a particularly chilly part of the UK. 

Sowing Mustard Seed

Mustard leaves offer the flexibility of successive sowings. They can be planted in spring to yield leaves suitable for salads, sown in August or September for overwintering within a polytunnel, or planted outdoors during late summer or early autumn to serve as green manure.

Seeds can be planted outdoors for cultivation between March and September, with timing dependent on location and desired outcomes for the mustard crop. Additionally, micro-green enthusiasts can sow seeds indoors throughout the year to enjoy a continuous harvest.

Mustard will not grow as quickly over winter but if you planted some in late summer then you could have some plants from which you will be able to harvest all through the coldest months. Successional planting will allow you to enjoy fresh and spicy salad leaves pretty much all year round.

If you are sowing mustard for seed then it is usual to sow the seeds around three weeks before your last frost date in Spring. 

Mustards are often also used as a green manure or 'catch crop'. It is important to take care of the soil in your polytunnel beds and mustard is often sown after summer crops are removed and dug in after around six weeks to enrich the soil. Be sure to dig in the mustard before it goes to seed, or mustard will be popping up everywhere! With later sowings outside, you can also simply wait until the green leafy part of the plants dies back in the winter. 

Planting and Spacing

As the plants begin to grow, you may wish to thin them out to a spacing of around 20cm. You can eat the plants you thin. However, thinning is not always necessary if you wish to simply cut leaves for use as and when throughout the growing season. 

The spacing is more important for mustard plants that are grown for seed since the plants will be getting much bigger before they are harvested and will therefore use more resources in terms of the soil and water they require. Plant seeds as above and then thin to a spacing of around 12cm once the seedlings emerge.

How to Harvest and Store Mustard

Simply harvest mustard leaves as you want them for salads and stir fries and other recipes. These are best used fresh, as soon as possible after harvesting. 

If you have grown mustard for its seed, collect the seed pods when they are fully ripened but before they drop seed and dry these in or on paper before using or storing. Seed can be used fresh or dried and stored for later use.

Mustard Plant Productivity

Mustard plants grown for leaves can produce prolifically. A row of around a metre at recommended spacing will yield very roughly 1/2 -3/4 kg of mustard greens over the growing season.  

Each mustard plant grown from seed should yield approximately 10g of seeds, as a very rough guideline. So you will need to grow quite a few plants in order to be able to make your own mustard condiment using homegrown mustard seeds. 

Mustard Nutrition Facts

Mustard boasts a low calorie count and is devoid of significant levels of fat and cholesterol. It stands out as an excellent source of dietary fiber while also offering substantial quantities of iron, beta-carotene, and vitamin C.

How to Make Mustard From Seeds

Numerous methods exist for crafting a satisfactory basic mustard. Below, we provide a straightforward recipe yielding approximately 750g of superb mild French mustard, which is enough to fill four small jars.


  • 100g White mustard seeds

  • 400ml Water at room temperature

  • 200ml White wine vinegar or cider vinegar

  • ½ teaspoon of Salt

  • ½ teaspoon of Sugar

  • Pinch of crushed Chilli flakes


Prepare the jars and their lids by sterilizing them. Begin by washing them thoroughly in hot water. Next, place the jars and lids upside down on a baking tray in a preheated oven at 160°C / 325°F / Gas 3 for approximately 15 minutes. This process ensures that the jars are clean and sterile, ready to be filled with your homemade mustard.


To begin, grind the mustard seeds using a pestle and mortar or a food processor, aiming to break up the seeds rather than grinding them into a powder. Transfer the ground seeds to a glass container and add water, covering the mixture. Refrigerate for four hours or overnight.

Afterward, pour off approximately one-third of the liquid (keeping it for later use). Combine the mustard mixture, vinegar, salt, and sugar in a food processor, blending for a minute or two. If the mixture appears too thick, gradually add small amounts of the reserved liquid from step three until the desired texture is achieved.

Spoon the prepared mustard into the sterilized jars and tightly seal them with the caps. Allow the mustard to mature in the jars for about a month; thereafter, its flavour may gradually diminish. For optimal taste, plan to use the mustard within three months, storing it in the refrigerator.

Care Tips for Mustard 

Mustard care will of course vary somewhat based on what you are aiming to achieve. But here are some of the basic elements of care that you need to think about:


Mustard can grow in most soil types as long as the soil is moist yet free-draining. Though relatively unfussy about pH, mustards will generally do best in alkaline or neutral soil. So it may be best to grow in raised beds or containers if you have more acidic soil where you live. 

If you are growing mustard leaves in a container, you can choose a range of different options. Remember that to make the most of the space in your polytunnel you can use a range of vertical gardening techniques and hanging containers. Fill these with a suitable, peat-free potting mix to grow mustard for leaves quickly and easily. 


Water mustard well to prevent a check on growth that can cause plants to bolt in warm weather if you are growing a mustard for its leaves. Mustard grown for seed. Or that used as a green manure, will usually cope just fine with natural rainfall, though obviously in a polytunnel you will need to take watering into your own hands. 


A nitrogen-rich organic feed will give mustard plants a boost. Usually, these needs can be met through the application of an organic mulch, and perhaps through companion planting with legumes or other nitrogen fixers. When growing in containers, you might consider giving a liquid plant feed, for example one made from nettles, or a more general weed feed. 

Mulches and Row Covers

Good organic mulch materials for mustard are those with a high nitrogen content. You might consider laying a mulch of grass clippings or other green, leafy material around your plants. Such a mulch also helps suppress weed growth and conserves soil moisture. 

Row covers or mini polytunnels, or cloches, can also be beneficial to keep leaf mustards free from pests that can occasionally plague them. So adding these is something to consider if growing leaf mustards in raised beds or in the ground. 

Varieties of Mustard 

For cultivation, you can consider a wide range of mustards, that have different purposes. 

Brassica juncea – for oriental mustard greens - such as:

  • 'Dragon's Tongue'

  • 'Giant Red'

  • 'Golden Frills'

  • 'Green wave'

  • 'Osaka purple'

Mustards for seed – such as:

  • black mustard – moderately spicy

  • brown mustard – the hottest varieties. 

  • yellow or white mustard – milder, with the strongest powers of preservation. 

Then there are the types of mustard that are made using the seeds:

  • English (e.g. Colmans) Mustard – A hot mustard made with a mix of white and brown mustard seeds along with other ingredients. 

  • Dijon Mustard – A mustard hotter than typical French mustard with unripe grape juice in place of vinegar. 

  • American mustard – a very mild 'mustard' with turmeric added to give a bright yellow hue. 

  • Chinese mustard – an extremely hot mustard made with brown/black seeds. 

  • Wholegrain mustard – any mustard made with seeds that have not been ground down, typically made in a similar way to Dijon mustard. 

Common Problems for Mustard 


Weed management is crucial for successful mustard cultivation as mustard plants do not thrive well when competing with weeds. It's especially vital during the establishment phase. To minimize weed interference, planting mustard in closely spaced rows can help. 

When cultivating the soil, it's important to work shallowly to prevent damage to the roots, ensuring uninterrupted growth of the plants. By implementing these practices, growers can effectively control weeds and promote healthy mustard plant growth.

Insects and Diseases

Most mustard varieties are characterized by their fast growth and resilience, exhibiting minimal susceptibility to production issues. 

Rotating planting locations annually can further mitigate the risk of diseases, contributing to overall crop health. This practice of crop rotation helps prevent the buildup of pathogens and pests in the soil, ensuring continuous success in mustard cultivation.

Top Tips for Growing Mustard in a Polytunnel 

Mustard can make a great addition to a polytunnel garden whether you are growing it for its leaves or seeds, or using it as a cover crop or green manure. The key is to think carefully about what you want to achieve, and to integrate mustard into the overall plans you have for your polytunnel garden. 


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growing mustard in a polytunnel