Welcome to Top of the Crops - today, you will learn how to grow celery in a polytunnel. For more gardening insights, be sure to check out our blog Polytunnel Gardening too!
Celery makes a great polytunnel crop. Celery is a fussy plant that will need the perfect conditions in which to grow. Get those conditions right, however, and celery can be a great addition to the kitchen garden and can be used to great effect in soups and salads.
Celery, Apium graveolens var dulce, is a cultivated plant that derives originally from wild celery. The long fibrous stalks and the leaves can be eaten and are frequently used in cooking and for salads. Celery seeds are also occasionally used as a culinary ingredient.
It is of the same species as celeriac, the stem base or hypocotyl of which is eaten like a root vegetable, and is also less closely related to carrots and parsnips, parsley and a number of other related edibles in the Apiaceae plant family.
This is a biennial plant that should naturally produce flowers and seeds in its second year before ending its lifecycle. It is typically often grown as an annual of vegetable gardens.
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The key to understanding the requirements for celery is to look at the conditions where the wild variety, from which the cultivated variety derives, can be found. Wild celery grows in marshy ground and on boggy riversides.
Water management, therefore, is key to success when it comes to growing celery. Celery requires plenty of water, with soil that never dries out.
For this reason, it can be difficult to grow celery inside a polytunnel. That said, a polytunnel with a good irrigation system could provide these plants with exactly what they need and help to control the environment and lessen the incidence of pests and disease.
Celery has often been said to be rather difficult to grow. But it can actually be relatively easy to grow as long as you provide the right growing conditions and, most crucially, get the watering right.
Growing celery successfully begins with choosing the right celery to grow. Newer self-blanching and green varieties are typically easiest and most straightforward to grow.
You will find some variety suggestions towards the end of this guide that are good choices for growers in the UK. Many of the highest quality varieties are F1 hybrids specifically bred for good yields in our climate.
Celery is typically grown from seed and transplanted, though you may also be able to purchase starter plants from a garden centre or plant nursery and can plant these out into your garden after the last frost date where you live.
Since celery can be fussy about the conditions in which they are grown, it is a good idea to prepare your growing area the previous autumn.
Trenching is a common method for growing celery. Prepare a trench around 35-50cm wide and 30cm deep and fill it nearly to the top with plenty of good quality compost, or well-rotted organic matter. (This trench can also be prepared in March if it has not been seen to the previous year.)
Later, the remaining soil excavated from the trench would traditionally be used to mound up around the celery stalks to blanch them.
Though blanching is not needed for many modern varietals, and trenching is not essential, this can be a good method even when growing modern varietals with which it is not strictly necessary as it can help to create optimal growing conditions.
Celery can be direct sown but here in the UK it is best to sow relatively early indoors because this is a crop that requires quite a long growing season. It is also best to sow indoors because warm temperatures are required for successful germination.
Sow celery seeds indoors between the middle of March and early April, into pots, trays or modules filled with a suitable seed-starting potting mix. Cover them over just very lightly and place them into a heated propagator or in another location where temperatures of at least 15 degrees Celsius can be maintained.
One important thing to note when growing celery from seed is that the seeds can take up to three weeks or so to germinate – so do not give up too soon.
Check regularly for seedlings emerging and when they do, place the young plants in a bright location where temperatures remain above 10 degrees C.. The plants can be prone to bolting later if exposed to lower temperatures at this early stage of their life.
Once the seedlings are large enough to handle, prick them out and pot them on into their own individual containers.
Hold off transplanting celery into its final growing position until all risk of frost has passed in the growing area – typically towards the end of May or in early June.
Plant celery in a line along the prepared trench or in your well-prepared growing area around 20-25cm apart.
Once the celery stems are around 30cm tall, earth them up, mounding soil around the base. Alternatively, collars of cardboard or paper can be used to encourage blanching. Not all celery will require this treatment.
For green and self-blanching varieties, planting in a block so plants shade one another or planting in the shade of taller plants will be enough to aid blanching. When planting in blocks, the celery plants should be approximately 23cm apart from one another in each direction.
Celery need not be as difficult to care for as some people imagine. Really, it is not challenging as long as its basic needs – especially as pertains to water – are met.
One thing to note is that you should wear gloves and long sleeves when caring for celery as the plants can cause a skin rash.
Water, water and water some more. Keep the watering consistent throughout the summer and never, ever allow the plants to dry out. This is certainly one of the most important elements when it comes to celery care, and the area where many problems can arise if things are not done right.
A high nitrogen organic mulch once the plants are established can help performance and improve crops. The mulch will also help to prevent moisture loss from the soil and prevent weed growth to a degree.
To promote healthy growth and thick stems, it can be a good idea to add a high nitrogen organic plant feed to your celery plants in summer once the plants are established.
Placing nitrogen fixing plants nearby and chopping and dropping nitrogen rich plant material below your celery may also be beneficial in helping to make sure celery has the nutrients it needs.
If you are growing celery in containers, it can also be beneficial to feed your celery plants once a fortnight or so with a balanced, organic liquid plant feed like compost tea.
To avoid damaging celery stems with a hoe, it is best to hand-weed close around your celery crop. Weed little and often so that any weed problem does not grow out of control and the crop does not suffer due to the competition from unwanted plants.
Celery will be ready to harvest between August and October, as soon as the plants are large enough. Cut the stems off at the base with a sharp knife.
Generally speaking, celery should be harvested before the first frost, though trenched celery can survive into December with a little protection, especially if grown in a polytunnel.
If you place the base with the roots in water and harvest only the top, the celery will regrow and provide you with more celery. This is one of a number of common vegetables that you can regrow from scraps.
Celery is best used as soon as possible after you have harvested it. But it will keep for a couple of weeks in the fridge, in water, if you cannot use it right away. Celery can also be blanched and frozen and can then be kept for up to a year or so to be used in soups, stews etc...
Some varieties of celery recommended for growers in the UK are:
‘Celebrity’
‘Giant Pink’ - Mammoth Pink
‘Granada’
‘Hadrian’
‘Tall Utah 52/70’
‘Tango’
‘Victoria’
Celery problems often revolve around the environmental conditions or care having some shortfall or issue.
If the temperatures, especially in early growth, are too cold, or if there is insufficient water availability through the summer, celery can bolt and flower and set seed prematurely. Some varieties, it should be noted, are more resistant to bolting than others so you may wish to pick a variety with this in mind.
Unfortunately, in addition to encountering problems due to the growing conditions and care, celery can also encounter a number of pest and disease problems.
Slugs and snails, flea beetles, celery leaf mining flies and carrot flies are some of the pests to look out for and protect against when growing this crop. Covering the crop may be necessary where pests pose a serious problem. Boost biodiversity for natural pest control, and choose companion plants carefully.
Celery can also be affected by diseases such as celery leaf spot, for example. To minimise the chances of an outbreak, make sure that you remove affected leaves promptly, and avoid growing celery and its close relative celeriac in the same growing location over multiple years.
When growing in a polytunnel, consistently maintaining soil moisture for celery can be a challenge. It can be a good idea, therefore, when growing celery, to make sure that an automated drip irrigation system is installed so that human error when it comes to watering does not cause big problems for your crop.
Companion planting is beneficial in a polytunnel to maximise yields, make the most of your space and ensure plants and soil remain as healthy as possible. Good companions for celery include leeks and other members of the onion family, and members of the cabbage family. So you may wish to grow celery alongside these other crops.
Shubrook, N., (2023) Top 6 health benefits of celery. BBC Good Food. [online] Available at: https://www.bbcgoodfood.com/howto/guide/health-benefits-celery
