Top Of The Crops - Sweetcorn

Growing Sweetcorn In A Polytunnel

Sweetcorn, with the Latin name Zea mays,  presents challenges in cultivation across many regions of the UK. Nonetheless, the satisfaction of harvesting your own flavourful corn on the cob makes the endeavour worthwhile. This late summer delicacy from your own garden is truly unparalleled in taste and reward.

Sweetcorn will taste so much sweeter when you grow it yourself and can bring it to your table so quickly. Home grown sweetcorn tastes to good because the sugars in the kernels have not yet had the chance to convert to starch. 

While older varieties were difficult to grow in the UK, modern F1 varieties are ideally suited to growing in most of the UK. Further north a polytunnel offers the extra warmth and wind protection needed to grow sweetcorn successfully.

The Preferred Conditions for Sweetcorn

For optimal growth, sweetcorn requires ample warmth and sunlight throughout the summer. It thrives when placed in a location with full sun exposure, preferably sheltered from strong winds to prevent damage. It likes a fertile, moist yet free-draining soil. 

In colder and northern regions, it will likely require protection or an undercover growing position in order to do well. 

What You Will Need to Grow Sweetcorn

To grow sweetcorn you will need:

  • Sweetcorn seeds – varieties suitable for where you live. (See variety suggestions below.)

  • A suitable growing location – perhaps a polytunnel in colder and northern regions. 

  • Biodegradable pots/ soil blocks etc. when sowing indoors.

  • Facility to water your crop. 

  • Organic matter for use as mulch.

Preparing the Ground

Prepare the planting are for your sweetcorn by topdressing the area with plenty of organic matter and making sure that it is weed-free. 

How to Grow Sweetcorn

If you have enough space, where the growing needs for sweetcorn can be met, it can be a truly rewarding crop. But when you are choosing your seeds, you need to be sure to choose a variety that is suited to the conditions where you live.

How to Sow and When to Plant Sweetcorn

Seeds should not be sown too early as this is a crop that does require a bit of warmth. Sow inside in early to mid May for planting out in late May or early June or sow direct into the soil where they are to grow in late May, once all risk of night time chills has passed. 

Sowing indoors early is usually the best strategy in the UK. Seeds germinate best at between 18 and 21 degrees C. so a heated propagator makes this job easier. Seeds should be sown to a depth of around 2.5cm and should germinate within a couple of weeks. 

Avoid sowing or transplanting sweetcorn too early in the season. It's crucial to wait until all risks of frost and nighttime chill have subsided before planting these crops in your garden. Ensure that the soil temperature has reached at least 15 degrees Celsius before sowing or transplanting.

To reduce the risk of root damage during transplantation, you can grow your sweetcorn seedlings in biodegradable pots that can be planted with the seedling. Sweetcorn does not appreciate root disturbance. 

Sweetcorn is best grown in blocks that are ideally at least four plants wide and four plants deep. Plants should be spaced at between 30 and 45cm apart. For this reason, you will usually need a larger polytunnel if you wish to grow sweetcorn within it successfully.

The reason for planting in blocks is that sweetcorn is wind-pollinated and planting in this formation gives the best chances for the plants to be pollinated successfully by their neighbours. 

Three Sisters Companion Planting Plan

Perhaps the best known and most famous of all companion planting combinations is that known as the 'three sisters'. This is a combination of sweetcorn, beans and squash. 

Each of these three plants aids its companions in some way, and so the three crops are often grown together. Corn provides support for beans to climb. The beans fix atmospheric nitrogen and make it available to plants grown nearby. Squash shades the soil and provides some protection from certain pests.

Consider sowing green beans to climb the corn once it is growing strongly, and planting a squash or pumpkin nearby. 

Care Tips for Sweetcorn

It is important to plant the sweetcorn in fertile soil and to add additional nutrition through mulches and organic feeds as these are particularly hungry plants. It is also important to keep the plants watered, though sweetcorn is relatively resilient to drought.

Apply a generous layer of organic mulch around your sweetcorn to provide steady fertilization throughout the growing season. Ensure consistent watering for your corn throughout the season, aiming for around an inch of water per week. Once cobs start to form, supplement with a general-purpose organic liquid feed to promote healthy growth.


Regular weeding is essential, particularly when the plants are young. Exercise caution when hoeing to avoid harming the shallow roots. If you notice any exposed roots, add additional mulch or soil to cover them up.


Sweetcorn plants have the potential to reach heights of up to 2 metres, varying by variety, making them susceptible to wind disturbance, which can loosen roots and impede growth. 

If your plants are being swayed by the wind, consider supporting each one with a bamboo cane or creating a perimeter of canes around the block and connecting them with string. 

Alternatively, mound soil around the base of the stem to provide added stability. This technique encourages the development of additional roots in the extra soil, further securing the plants in place. When the corn is around 2ft high, mound up the soil around the base and mulch well to encourage strong rooting. 


Because sweetcorn relies on wind for pollination, it's advisable, as mentioned above,  to plant them in a block formation rather than in long rows. This arrangement ensures that the plants are surrounded by others, increasing the likelihood of successful pollination regardless of wind direction. 

Additionally, once the male flower-heads open at the top of the plant, you can lend a helping hand by gently tapping the stems to loosen the pollen. This action enhances the chances of pollen reaching the female flowers lower down the plant. Inadequate pollination can lead to poorly filled cobs.

Harvesting Sweetcorn

In the UK, sweetcorn is typically ready for harvest between August and October.  But when exactly you will harvest the sweetcorn depends on a range of factors including which specific variety you are growing, where you live and the conditions there, the weather in a given summer and when exactly you sowed/ planted your crop. 

(Going for an early maturing sweetcorn is generally a good idea when growing corn in the UK, and especially if you live further north, it is important to choose one which is suitable for colder soils and cooler summers. These will have a better chance of maturing successfully before colder weather arrives once more.)

To determine if your sweetcorn is ripe for picking:

  1. Inspect the tassels on top, and consider harvesting when they begin to turn brown.

  2. Prior to harvesting, gently peel back the husk around the cob and examine the kernels. They should release a milky fluid when pressed with a thumbnail.

  3. Once the fluid is milky rather than clear, it's time to harvest. Remove each cob with a sharp twist and a gentle tug.

  4. Sweetcorn should be consumed or preserved immediately after harvesting to maintain freshness – time is of the essence.

How to Prepare and Use Sweetcorn

Remove the husks and silky tassels from the sweetcorn and snap off the stalk. Steam, microwave, or barbecue the cobs until they are al dente, then garnish them with butter if desired. There are many sweetcorn recipe ideas to consider. 

How to Store Sweetcorn

Sweetcorn can be stripped from the cob and frozen, or dried in an oven or dehydrator. You can also blanch and then freeze whole cobs by boiling them for four minutes, draining them, then placing them into suitable freezer containers and placing them in your freezer. 

Varieties of Sweetcorn

Some varieties of sweetcorn recommended for UK cultivation are:

  • Earlibird'

  • 'Lark'

  • 'Mirai Picnic'

  • 'Ovation'

  • 'Swift'

Common Problems for Sweetcorn

Most problems that arise when growing sweetcorn involve problems with the environmental conditions or care. Too little sun, temperatures that are too low, and providing either too much or too little water are commonly the root causes of issues. 

To prevent undesirable cross-pollination, it's best to avoid planting 'supersweet' varieties alongside standard varieties of sweetcorn. Similarly, be cautious when growing sweetcorn near maize crops or ornamental maize varieties, as this can lead to starchy kernels with diminished flavour.

Common Sweetcorn Pests

There are a number of common pests, including birds, squirrels, mice and other rodents, that love eating sweetcorn as much as we do. You may therefore need to employ physical barriers to protect your crop and make sure you get to eat it before the pests do. 


Protect young sweetcorn seedlings from bird damage, particularly from pigeons, by covering them with netting. This barrier will deter birds from pecking at the leaves and potentially destroying the plants. Additionally, taller sweetcorn plants are less attractive to birds, so as the plants grow, they become less vulnerable to bird attacks.

Slugs and Snails

Young sweetcorn seedlings are susceptible to damage from slugs and snails, which can be identified by the slime trails they leave behind and the visible damage to the plants. As the seedlings grow taller, they become less vulnerable to these pests. 

To mitigate slug and snail damage:

  • Check plants during the night and manually remove any slugs and snails.

  • Apply crushed eggshells or grit to the soil around the plants, as this may help deter slugs and snails to some extent.

  • Attract predators to your garden – creatures that will eat these pests and keep their numbers down. 


To prevent mice from digging up and consuming sweetcorn seeds sown in the ground:

  • Use protective measures such as placing hardware cloth or wire mesh over the planted area to deter mice from accessing the seeds.

  • Alternatively, sow sweetcorn seeds in containers or raised beds with barriers that mice cannot easily breach.

  • Keep the garden area clean and free of debris, which can attract mice and provide hiding spots.

  • Again, attract nocturnal hunters to your garden to prey on rodents and keep their numbers in check. 

Top Tips for Growing Sweetcorn in a Polytunnel 

A polytunnel can make it easier to grow sweetcorn in many parts of the UK, and may be necessary where it is colder and more challenging to grow sweetcorn successfully outside. 

But make sure you water well to prevent any issues, remembering that in a polytunnel you will have to meet all the water needs of your plants since they will not naturally receive rainfall. 

Take care to maintain good airflow and ensure that you aid in pollination by tapping or gently shaking your plants, since wind will not be as able to do the job for you inside a polytunnel.

Make sure you think carefully about companion plants and layout – make sure sweetcorn only shades other plants where this is desirable and not where it is not. 


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BBC Good Foods. (2020). Sweetcorn recipes. [online] Available at: [accessed 20/03/24]

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growing sweetcorn in a polytunnel