How To Grow Sweetcorn – A Complete Guide

The incredible taste of freshly harvested sweetcorn is something that can never be replicated in the supermarket. And sweetcorn is healthy too, because it is high in fibre.

Sweetcorn has a reputation for being very difficult to grow, but this guide will teach you how to grow sweetcorn from seed successfully.

Which Sweetcorn Variety To Grow

different sweetcorn varieties

From commercial hybrids, heritage varieties, coloured and mini sweetcorn there are a lot of different options available here. So which is best to grow?

For anyone who is starting out for the first time, the mini sweetcorn varieties are the perfect place to begin. They are quick growing, tasty and very easy to get a good crop from.

For those who are a little more experienced, I would highly recommend heritage varieties. They are developed for our climate, have a wonderful taste and are very reliable.

Commercial hybrids are usually designed to produce a lot of cobs of corn. In many cases, these will not all ripen in a garden setting.

The taste is very sweet in commercial varieties, but I find the heritage varieties to be more flavourful. The main problem with hybrids is that all the sweetcorn will ripen at the exact same time, giving a huge sudden glut and, as sweetcorn tastes best within a few hours of harvesting, storage of this glut can be difficult.

I wouldn’t recommend sweetcorn hybrids in a garden.

So here are some varieties of sweetcorn I would recommend you try:

Damaun: this heirloom sweetcorn is juicy and sweet. It’s also a popular heritage sweetcorn variety.

Popcorn Fiesta: This is multicoloured heirloom variety. The kernels are a mixture of red, blue, yellow, purple, black, white and gold. This variety originates from South America and will look fabulous in your garden and your plate. They are perfect for popcorn.

Minipop F1: This mini or baby sweetcorn variety gives you sweet and tender cobs that work great in stir-fries. They are great if you don’t have much space. 

Now let’s get down to the nitty-gritty of how to grow sweetcorn.

How To Grow Sweetcorn From Seeds

sweetcorn seedlings

To get a good crop in the UK, you really need to be sowing your seeds indoors before the last frost. In a cool greenhouse or windowsill, sowing can begin as early as April and continue until early May.

Sweetcorn can be successful if sown directly outdoors, but given the unpredictable weather, your crops are really reliant on having a very warm summer.

Sowing indoors will give the plants the chance to establish before the weather is good enough outdoors. Sweetcorn plants really do not like to become pot bound or their roots restricted, so growing in a large pot, roottrainers or toilet roll inners is a good option.

Alternatively, you could try growing them in soil blocks.

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You want to sow your sweetcorn seed about 2.5cm (1in) deep. The seeds are quite large, so one per pot is best.

If you want to sow your sweetcorn seeds directly outdoors, you have to make sure that the soil temperature is warm enough. It should be above 10°C. 

You can use a soil thermometer to check the soil temperature, if you are unsure.

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Don’t grow sweetcorn in rows, as this could result in poor pollination. Sweetcorn is not pollinated by bees and other insects, but by wind. So sowing your sweetcorn plants in blocks, will help with the pollination.

Now we come to the next step of how to grow sweetcorn from seeds, transplanting the sweetcorn seedlings.

Growing Your Plants On

Once established, your sweetcorn plants can be planted out after the last frost.

It’s essential that you don’t plant outdoors until there is no more danger of frost, as sweetcorn plants are very vulnerable to cold weather.

This will be very dependent on your area and varies yearly, but late May or early June are usually the time to be transplanting outdoors, as there is no more risk of frost.

Before being planted outdoors, you will need to harden your sweetcorn plants off to acclimatise them to the outdoor weather.

This is done by placing the plants outdoors during the day for at least 7 days prior to being planted outdoors. This can be on a patio, an unheated greenhouse or a cold frame.

The planting out location is important. Sweet corn need a sunny spot, where they are in full sun and are also sheltered from wind.

Sweetcorn is a very hungry crop, so you need to prepare the ground to ensure you plant your sweetcorn seedlings in rich and moist soil.

You can do this by mixing organic matter into the soil, such as well-rotted compost or green manure

If a good layer of manure is added then no further feeding will be needed, if the soil isn’t very good a liquid feed will be needed later in the season.

As mentioned earlier, the plants must be planted in blocks rather than rows to allow wind pollination. Plant out at spacings of 35-45 cm (14-18in) apart. You will need at least 8 plants in a block to allow good pollination.

Sweetcorn Top Tips

ripe sweetcorn

In this guide about how to grow sweetcorn we also include some things you can do that will significantly increase your success with sweetcorn.

  • Watering when dry is very important. Although sweetcorn can survive drought quite well, the growth slows down when the plants are not watered regularly. Due to our short growing season, keeping the plants well watered will often give you a crop 2-3 weeks earlier.
  • When the tassels begin to show tap the plants daily to release the pollen and increase germination.
  • If you are growing a small number of plants or are in a very windy location, it might be best to stake the plants, they can break in strong winds.
  • Finally, if your soil isn’t good a regular feed of liquid seaweed will increase growth. Mulching with grass, compost or well-rotted organic matter will keep the moisture in the ground as well as feeding the plants.

When To Harvest Sweetcorn

Now we come to the best part of our guide about how to grow sweetcorn, harvest.

Not being able to see the inside of the sweetcorn cob can make it seem difficult to tell when the sweetcorn is ripe.

Watch out for the tassels of the sweetcorn turning a dark chocolate brown colour.

This will be any time from late July to September depending on the season. Once the tassels are dark brown it’s a good indication that the sweetcorn are ripe.

To check the sweetcorn are 100% ripe, you can pull back some of the leaves from the cob and squeeze a grain in between your finger. If the liquid that comes out is a creamy yellow colour, the corn is ripe.

The cob will pull from the stem easily. Just twist the cob and remove it from the stem.

Sweetcorn are best eaten straight from the plant. Within an hour, they begin to lose the flavour. Pick as close to dinner as possible to guarantee the best flavour possible.

The cobs of corn cannot easily be stored. You can remove the corn from the cobs and freeze it, but the taste will never be as good as freshly harvested sweetcorn eaten straight from the plant.

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Pests And Diseases Affecting Sweetcorn

two yellow sweetcorn on plant

No guide about how to grow sweetcorn would be complete without a section about pests and diseases.

Diseases

You will be very pleased to read, that sweetcorn is not vulnerable to diseases.

However, like any plant, fungus and bacteria might infect sweetcorn plants if they are not healthy. So, to make sure they stay healthy, follow these tips:

  • Space your plants out enough to ensure they have good air circulation, because many diseases occur in damp conditions.
  • Water them from below to keep the foliage dry.
  • Water your sweetcorn plants regularly in dry weather, to ensure the soil stays moist.
  • Weed regularly around the sweetcorn and remove any dead plant debris, as these could host diseases.
  • Corn roots are quite shallow, so make sure they are secure in the soil after a windy day.

Pests

It’s another thing with pests. But don’t worry, this guide about how to grow sweetcorn will tell you how to keep any pests away from your sweetcorn.

Mice love sweetcorn seeds and will eat them all, if given a chance.

You could try and trap them, but not only is this not as easy as it sounds, it does also involve killing them.

So the best way to prevent mice becoming a problem for your corn seeds is to start them off in pots. And only plant them out when they are established. 

Mice won’t be a concern any more.

However, birds could still cause a problem, especially pigeons, who love sweetcorn seedlings.

Pigeon on garden feeder

But that is easily solved too, just cover your young sweetcorn plants with bird netting. 

Once they have grown to a good size, the pigeons will leave them alone.

Slugs and snails also love sweetcorn plants, especially young ones. And they can ruin your whole crops if you let them.

Again, they like young plants, so once your sweetcorn is well established, the danger is over.

Here is how you can protect your young plants from slugs and snails:

  • seedlings can be protected by covering them with bottles. Just cut a bottle, squash bottles work well, in half and put the bottom half over the sweetcorn seedling. You can cover the top with a bit of netting to make absolutely sure.
  • You can also grow companion plants with your sweetcorn that will repel the slugs and snails. Plant borage, lavender, chamomile, comfrey or wild garlic around your sweetcorn to ward off the slimy pests.

We don’t recommend the use of slug pallets, as these will kill them. And while slugs and snails are one of the most annoying pests, they are also very important for our ecosystem.

Therefore, we prefer ways to keep them away from our vegetables without harming them.

Now that we have shown you how to grow sweetcorn in your own garden, why not go and get some seeds and get started. You will love the taste of the freshly picked sweetcorn!

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