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Alan's Edible Plant of the Month; Sweet Corn

Published on August 18th 2019
Sweet corn on a cutting board

This is the start of a new monthly series in which I will be highlighting some of my favourite edible plants.

We're kicking off with one of my favourites. Sweet corn is one of those must-grow vegetables that taste the best when they are fresh. You can also grow super sweet varieties at home that farmers might not be so keen on growing.
In this article, I'll cover where, how, and what to grow. I'll also talk a bit about harvesting, freezing, what to grow with them, and what to do after they have finished. I hope this will inspire you to grow sweet corn!
Also, watch out for my monthly piece on ornamental plants! This month it covers that excellent shrub, the Hydrangea!
Hydrangea lace-cap flowers

Everything You Need to Know About Hydrangeas


Where can they grow?

Sorry but for those living high on the Pennines or Welsh and Scottish Mountains, this one is going to be a challenge.
For the rest of us down at lower levels, sweet corn is an easy crop. You can even grow a few in pots on the balcony.

What conditions do they like?

Sweet corn is a summer crop that is frost tender. It needs summer days of long day-length to grow strong enough to produce a cob or two per plant.
It loves fertile, well-drained soil and once established will tolerate dry conditions.
This vegetable will pay you back if you feed it well and relishes soils with high organic matter or has had well-rotted manure added before planting.
Sweet corn loves the sun, so not one for planting under that apple tree or on the north side of your house!
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How can I grow it?

You can sow sweet corn seed into the soil.
However, it is better sown in containers under protection. I use Haxnicks Rootrainers for my sweet corn sowing as they produce an excellent root system that transplants well.
Sweet corn planting from rootrainers
Planting out plants from Haxnicks Rootrainers
Sow into any good seed or potting compost because you will be planting them out quickly after germination.
Aim to sow from the end of April through to mid-May. If you live in a cold area, then it will pay to plant later. However, don't leave it too late as sweet corn needs summer days to grow well.

Plant in a block

Most vegetables are planted in nice straight rows so that it's easy to hoe out the weeds. But with sweet corn, it is best to plant in blocks and not long thin rows.
This is because sweet corn needs to be cross-pollinated by the wind. So if you plant in a block, then the pollen hasn't so far to go!
Sweet corn flower tassels
The female tassels of sweet corn
You'll find the female flowers sticking out of the end of the cobs and the male flowers on the top of the stem.

Get them off to a good start!

There's an adage I've picked up that says that you need to have your sweet corn 'knee-high by the fourth of July.' This is just an indication that the plants need to be big enough before they flower to get a good crop.
Sweet corn and author among sweet corn plants
Knee high by the 4th of July

Best varieties to grow

Newest varieties are often the best as breeders are constantly looking for varieties suited to our relatively cool summers.
I would recommend growing super sweet varieties. These are so sweet that you can eat them raw. If you decide to go with a super sweet variety, it is best to stick to only one variety.
If you're growing more than one super sweet variety, it pays to plant them some distance apart to avoid cross-pollination between varieties, as this reduces the cob quality.
Many varieties have been developed to mature early but often at the expense of yield.
At the moment I would recommend growing 'F1 Sundance', 'F1 Swift' or 'Swift'. However this year I'm growing 'Goldcrest', and it's looking superb so far!
Sweet corn cobs in a bowl
Sweet corn 'F1 Sundance'
You might be tempted to grow mini sweet corns, especially if you like to stir fry cook them. I've tried these in the past but found them disappointing.
There is an increasing interest in growing multi-coloured sweet corn cobs, but I can't say that they will tempt me away from the conventional super sweet varieties.

How do you know when they are ready?

It's hard to judge when your sweet corn cobs are ready to harvest, but I have a couple of tips.
  • When the tassels at the top of each cob start to go brown and dry, then the kernels inside - the bits we eat - are generally ready.
Sweet corn cob ready to harvest
The tassels on the cob wither when the cob is ready to harvest
  • Peel back a bit of the outer cob sheath to reveal the kernels. If you push your thumbnail into a kernel and it should release milky white sap, which means that it's ready to harvest.

Can I grow another crop with sweet corn?

You most certainly can! I grow an adaption of the technique that the Native American Iroquois used to get them through harsh winters. This technique spread throughout many parts of North and Central America.
Under my sweet corn, I plant squash to cover the ground, but I also sow climbing beans to climb up some of the sweet corn stems.
These crops have different nutrient and growing needs. So I'm getting three crops from one patch that complement one another.
This year I've added a fourth crop - sunflowers. Read more about it here:
Squash plant under sweet corn
Squash plants under planted for the three sisters method.

After harvest

Sweet corn freezes well; they only need a quick blanching in boiling water and then cooling as quickly as possible in icy water.
After the harvest, plants can be cleared away and added to the compost heap. However, they take longer to break down than most other vegetables so I'd recommend passing them through a chipper to shred their tough stems.
When your sweet corn is cleared, you could plant spring cabbage plants. Alternatively, sow winter salad vegetables such as corn salad, land cress or mizuna.
You might even grow a green manure crop to improve your soil.
Later in autumn, you could sow winter hardy broad beans and peas.

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