Welcome to Top of the Crops! Today, you will learn about growing brussel sprouts in a polytunnel for UK gardens! For more gardening advice for beginner or professional gardeners, check out our insightful blog Polytunnel Gardening.
Brussel sprouts are a vegetable loved by some and loathed by others. If you are not a convert then you might want to grow your own, so that you can try out some new recipes with new varietals, that tend to have a milder, better flavour than those you may remember from the past.
Though not the easiest member of the cabbage family to grow, Brussels sprouts are not too challenging. They can be a great choice for domestic or commercial polytunnels or outside gardens, to provide yields over the coldest part of the year.
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Brussels sprouts are unusual looking brassicas, which grow up to a metre or so in height. They have leafy tops, and stems covered with small, rounded sprouts that are green or sometimes purple in hue.
There are many great modern varieties to choose from if you would like to grow Brussels sprouts in your garden.
The key things to remember are that Brussel sprouts need:
A full sun location, ideally fairly sheltered.
Fertile, firm and moist yet well-drained soil, with a neutral or mildly alkaline pH.
A long time to grow. They are planted in spring but won't be ready to harvest until the following late autumn or winter.
Protection from pests with a physical cover of some kind.
To grow Brussels sprouts you will need:
Brussels sprouts seeds.
Seed trays/ small pots/ soil blocks, and seed starting growing medium.
A suitable growing location.
A trowel/ spade for planting out.
A row cover, mini polytunnel or protective mesh to protect from pests.
Facility to water your crop throughout the summer.
Garden shears or sharp knife for harvesting.
Organic matter for mulching.
As well as thinking about choosing a location that can provide the basic environmental growing conditions that Brussels sprouts need, you should also consider how these plants will fit into your overall garden plans. Remember that they will remain in the growing area all season – over a considerable length of time.
Before sowing or planting Brussel sprouts, make sure that you prepare the area well, introducing plenty of organic matter and ensuring that the soil is healthy and the area is weed free.
Since Brussels sprouts need a long time to grow, it is a good idea to sow them indoors early in the year, or to direct sow them outside under cloches or other protection. You can sow early, mid and late season varieties to enjoy harvests over the longest period of time.
If you decide to start the seeds indoors, then you should do so between February and April. Sow into modular trays, biodegradable pots or soil blocks so as to minimise root disturbance. Sow the seeds around 1cm deep.
Plant out the young plants after the last frost in your area, once they are at least 10cm in height.
Alternatively, you can sow into prepared growing areas outdoors or in a polytunnel between around March and May.
Outdoors, Brussels sprouts are often sown into separate seed beds so that they don't take up space in the main vegetable growing areas when space it at a premium in spring. But you can also sow directly into your main vegetable beds if you prefer.
Sow under cloches or row covers to protect the seeds and seedlings, and also to provide slightly warmer conditions if the weather is still quite cold.
If you are sowing in a seed bed, sow the seeds 1-2cm deep, sowing thinly and thinning to 7.5cm spacing once they are large enough to handle. You can eat the young seedlings you thin.
If you are sowing Brussels sprouts in their final growing positions, sow several seeds at stations around 60cm apart, thinning out once seedlings emerge to leave just one seedling at each station.
A large part of the puzzle when learning how to successfully grow Brussels sprouts is finding the right place to grow them.
As mentioned above, Brussels sprouts need a sunny spot with moist yet free-draining, fertile soil. They like to be grown in a well-prepared bed that has been firmed well and amended with plenty of organic matter.
In rotation, this crop should be planted and rotated alongside other members of the brassica family. It can be beneficial to have these and other cabbage family plants follow peas, beans or other legumes in rotation, because of the legumes nitrogen fixation and the fact that these leafy green vegetables have relatively high nitrogen needs.
In companion planting, Brussels sprouts and other brassicas may benefit from having legumes planted alongside them. Beetroots are also said to be good companions, and you might consider planting a quick growing crop like lettuce between your Brussels sprouts which will be harvested before they really need the space. There are also plenty of other companion plants for brassicas to consider.
Harden off and plant out Brussels sprouts between April and June, when the plants are around 10-15cm tall. Spacing of around 60cm between plants and 75cm between rows is generally recommended.
When you are transplanting young Brussels sprouts into their final growing positions, it is important to try to keep root disturbance to a minimum. This is why, when sowing indoors, biodegradable pots or soil blocks can be a good idea.
Make sure that you place them carefully into a planting hole so that they sit just a little deeper in the soil than they were before, with their lowest leaves level with the surface of the soil. Make sure that you firm the soil around them well so they are well anchored in place.
It is best to cover your crop in order to prevent pest problems, especially early in their growth.
Brussels sprouts can be harvested from September onwards though most varieties are harvested during the winter months. In fact, it is often best to eat sprouts after they have been touched by frost as this makes them a little sweeter.
The sprouts are harvested from the base of the plant upwards, once they reach around walnut size, and are still firm and tightly closed. You can harvest them little and often as required over a relatively long period and pick more as and when these form.
Modern cultivars often produce sprouts all at once up the length of the stem. So with these types you can harvest the whole stem if you prefer. However, you can also simply leave the stalks standing and harvest sprouts as you need them through the winter months.
Once the cropping comes to an end, the sprout tops can also be harvested and cooked like cabbage or spring greens.
There are plenty of great recipes that help you make the most of your main Brussels sprouts crop.
Brussels sprouts are not too challenging to care for as long as you remember their basic environmental and growing needs. Though it is best to cover them to prevent pest problems.
Water Brussels sprouts on a regular basis especially while they are seedlings and young plants. Once they are well established, they will need additional watering only when grown undercover or when the weather is very dry over a prolonged period. If there is no rain, water well, at the base of the mature plants, every 10-14 days or so.
Apply a thick layer of well-rotted manure or homemade compost around the plants in order to conserve soil moisture, provide slow-release fertility, protect the soil and reduce competition from weeds.
In addition to mulching, it can also be a good idea to give plants a boost by providing them with a nitrogen-rich organic fertilizer. The RHS recommends dried poultry manure pellets at a rate of 150g per square metre.
While the sprouts are young, it is important to stay on top of weeds so that there is not too much competition.
In around August, towards the tail end of summer, mound soil around the base of Brussels sprouts' stems to anchor them more firmly and provide extra support. Taller plants may also require some form of stake or other support to prevent wind-rock and keep them in place when autumn storms arrive.
RHS award of garden merit (AGM) varieties are a good place to begin when choosing which Brussels sprouts to grow. The varieties which currently have an AGM are:
‘Abacus’
‘Attwood’
‘Brodie’
‘Cascade’
‘Clodius’
‘Crispus’
‘Doric’
‘Green Marble’
‘Igor’
‘Marte’
‘Maximus’
‘Montgomery’
If you would like to be able to eat your own Brussels sprouts for Christmas, you can sow late varieties the previous spring. These should be placed into their final growing positions in June and should then mature and be ready to harvest between December and the following March.
Remember, the best option is often to leave the sprouts on the plants until they are needed. But you can also freeze sprouts for later use if you wish.
Brussels sprouts take their common name from the European city. Though this cabbage species originates in the Mediterranean region, it was first grown in northern Europe during the 5th century and was later, perhaps even as early as the 13th century, cultivated near the city of Brussels in Belgium, and came to be associated with that place during the 16th century when they were particularly popular in that region.
Like other brassicas, Brussels sprouts are generally robust and hardy plants but they can have issues with a number of pests and diseases such as pigeons and other birds, caterpillars, whitefly and aphids, cabbage root fly, and club root.
Covering the crop and companion planting are usually the best ways to reduce serious problems and ensure that you get a good yield.
If the sprouts are open rather that the closed globes you expect, this may be due to poor or inadequately firm soil.
Brussels sprouts might not be the first crop you think of for a polytunnel garden. You may prefer to grow these space hogs outside. But there is a lot to be said for growing these under cover. It will not only help with protection from pests but will also reduce issues with wind rock and plants blowing over in strong winds in autumn and winter.
Just remember that the plants will benefit from some exposure to frost, so don't cozen them too much or they simply won't taste as good.
Make sure you think about companion planting and crop rotation when growing sprouts in a polytunnel to get the best possible results.
Lowder, C., (2023) 42 Brussels Sprouts Recipes Even Haters Will Love. Delish. [online] Available at: https://www.delish.com/cooking/g1409/brussels-sprouts-recipes/ [accessed 15/12/23]
