Welcome to Top of the Crops - today, you will learn how to grow spinach and swiss chard in a polytunnel. For more gardening insights, be sure to check out our blog Polytunnel Gardening too!
Spinach and Swiss chard are two leafy plants that can be great additions to a domestic or commercial polytunnel. Both are plants that produce an abundance of leafy green leaves that can be eaten in salads and in stir fries and a range of other recipes throughout the year.
There are many different leafy green vegetables to grow in a polytunnel garden. Two of the most useful and important are spinach and chard.
True spinach, Spinacea oleracea, is a slightly more delicate crop, and can be prone to bolting.
Swiss Chard, and other related crops such as 'perpetual spinach' or Spinach Beet, as it is sometimes known (Beta vulgaris subsp. vulgaris Cicla Group and Flavescens Group) will continue to produce for a longer time and are less prone to bolting.
Since these excellent chards (like beetroot but without the bulb) taste very like true spinach, they are often an easier option for polytunnel growers and other home gardeners. Though both of these crops can be worth growing in your garden.
Chards are far more forgiving and can also be grown in a polytunnel all year round, often with only one sowing that just keeps on giving. There is not only Swiss chard, but also types known as perpetual spinach, and bright lights and rainbow chards that are as decorative as they are delicious. The leaves are cut and come again and should regrow as long as a small stump is left.
Where you should place your crops and the conditions that they require largely depend on which specific leafy green you have chosen to grow and – crucially – when.
Winter cultivars will require a sunny spot while summer types benefit from some shade and will tend to bolt in hot weather if they are in full sun all day.
Make sure that the soil or growing medium is rich in nutrients and contains plenty of organic matter for best results when growing any of these types of crops.
Swiss chard can be sown once in the spring and then in summer and then potentially harvested throughout the whole of the year. If you are new to growing your own food then this is an easier place to start than true spinach.
To grow chard:
Select and source seeds for the chard you wish to grow.
Choose a growing location – remembering the growing requirements mentioned above.
Sow the seeds – two sowing traditionally provide a year-round harvest – one sowing in April and the next in July – the second crop, overwintered, will provide leaves the following spring when growth resumes. You can also sow every few weeks between March and August for regular harvests of baby leaves.
Start the seeds either indoors in modules of seed-starting potting mix around 2.5cm deep for an earlier crop, or where they are to grow to the same depth, around 5-10cm apart along rows spaced around 45cm apart in spring or early summer.
Transplant (when around 5cm tall) or thin to give an eventual spacing of 30cm between plants if you wish them to mature to full size, or just 5cm apart if you are aiming for baby leaves.
Chard, and spinach too, are both good choices for container growing, for raised beds or for growing in the ground. These crops can be accommodated in a range of different settings.
Remember that for both of these crops the soil should be fertile, humus-rich, moist yet free-draining. Make sure that you add plenty of organic matter before sowing/ planting. Adding an organic fertilizer before planting can help to ensure good results.
True summer spinach (Spinacia oleracea) is usually sown in spring between March and May. You can also sow later, towards the end of summer or in the early autumn, for overwintering.
As with chard you can make a couple of annual sowings for a year-long harvest, or (the recommended option for beginners) successional sow for baby leaves so that bolting is less likely to become an issue.
If you wish, you can sow spinach indoors for later transplantation. However, note that this can be risky and transplantation can trigger the plants to bolt. Sowing spinach into individual modules and using biodegradable pots/ modules to avoid root disturbance can help.
Sowing directly where the crop is to grow limits the chances of bolting by avoiding the need for transplantation.
The seeds can either be sown in spring/ early summer, or in late summer/ autumn. They are usually sown into drills 2.5cm deep and around 20cm apart or sown into containers at least 30cm across so that they are large enough not to dry out too quickly. Sowing batches every few weeks can help to provide continual harvests of spinach throughout the year.
If you are growing spinach for baby leaves, thinning direct sown seedlings will not usually be required. But for full-sized plants you should thin out seedlings to around 7.5cm spacing when they are big enough to handle, then harvest every second spinach seedling a few weeks later to use in salads so that the remaining ones have the space to grow.
Growing true spinach is all about making sure that the plants are not stressed in any way, as any stress will typically trigger bolting.
Here are the basic things that you need to do to care for these crops correctly:
Both true spinach and chards will require plenty of water throughout the growing season, though chard is more tolerant of less than ideal conditions and is far less prone to going prematurely to seed. Make sure that you water well and consistently, aiming water at the base of the plants and trying not to wet the leaves.
Both true spinach and chards are leafy greens that will benefit from top dressing with a mulch that is high in nitrogen and/or nitrogen rich liquid feeds.
It can also be important to think about competition. Weeds between your plants can take away the water and nutrients these plants require. So make sure weeds do not get out of control.
Note however that not all neighbours are bad ones. These leafy greens with their high nitrogen needs may benefit from having legumes or other nitrogen fixing plants close by.
Your goal when growing spinach is to prevent the plants from bolting, and flowering and setting seed prematurely. This is often easier said than done but you can hold this back by ensuring ideal growing conditions and avoiding any stress on the plants.
Sooner or later, however, a flowering stalk will appear and edible leaves will stop being produced, marking the end of the harvest period. You should remove and compost your spinach plants at this time as they will not produce further yields.
Hardier varieties of spinach or chard should be fine in a polytunnel, though may require an additional layer of protection from cloches or row covers if the winter or the location is particularly cold.
Spinach can be harvested early, for baby leaves or even micro-greens, or once mature after a couple of months. Leaves may simply be harvested as soon as they are large enough to pick.
Pick true spinach from summer types between late May and the end of October and winter cultivars between October and April.
Chards can be harvested any time throughout the year. You can either take leaves a little at a time from plants as needed, until the plants begin to flower, or you can wait until the plants are well established and then cut them off at the base. When cut back all at once, the plants, if healthy, should regrow once more from the stumps.
Start from the outside leaves of chard. In summer you can take up to half of the leaves in one go, while you should be more sparing when harvesting from winter crops.
Of course, there are plenty of spinach recipes, and chard can also be used in many of the same ways.
AGM varieties of chard and spinach are a good place to begin when choosing which specific ones to grow in your garden.
When it comes to chard, you might try:
And when it comes to true spinach, these are some excellent options:
Beyond these options you might also consider many other plants commonly called by names that include the term spinach, such as:
Lincolnshire spinach – AKA Good king Henry – Blitum bonus henricus.
Red mountain spinach or red orach - Atriplex hortensis var. rubra
Tree spinach - Chenopodium giganteum
New Zealand spinach - Tetragonia tetragonoides
Malabar or Indian spinach - Basella alba
Bolting is of course the main problem encountered when growing spinach. Keep plants well-watered, in the right growing location, and out of extremes of temperature to delay flowering.
Slugs and snails, birds and other pests can sometimes be a pest of both spinach and chard, especially vulnerable while they are young. So look out for pests and use physical barriers where necessary to protect your crops.
Look out for fungal issues like downy mildew or grey mould in warm, humid weather. Make sure you have good air flow around the plants to reduce the chances of this problem.
Think about companion planting. True spinach in particular will benefit from nearby companion plants which can shade it from the sun in the height of summer, such as peas and beans. Brassicas and spinach may also benefit one another when grown as companions.
Think about planting towers and other vertical gardening solutions to fit in more of these leafy vegetable crops into your polytunnel garden.
How long does it take to grow spinach?
Spinach will be ready to harvest as few as 6 weeks or so from sowing as baby leaves, though for larger leaves you will need to wait a little longer.
Yes, as long as you leave a stump at the base of the plant, new leaves should regrow from the root section a couple more times, as long as the roots remain in good health.
Harvest the outer leaves from the plant so that the central ones continue to grow, so that you can crop from individual plants over a longer harvest period.
Williams, J., (2023) Top 10 health benefits of spinach. BBC Good Food. [online] Available at: https://www.bbcgoodfood.com/howto/guide/ingredient-focus-spinach
Butler, N., (2023) Health benefits of Swiss Chard. Medical News Today. [online] Available at: https://www.medicalnewstoday.com/articles/284103