Sweet Corn

Even though sweet corn is the least productive vegetable per square metre, I wouldn't want a summer without any.

The taste of organically grown sweet corn freshly picked and steamed with a knob of butter for dinner is to die for.

Sweet corn needs to be grown in nitrogen rich soil with plenty of water.

Side dressings of blood and bone should be given weekly until the corn starts to send up its pollen stems.

It then needs a side dressing of sulphate of potash to ensure good flowering and even cob set.

Sweet corn is best grown in blocks of 3x 4-8 plants in the home garden with 30 cm 30cm spacing.

Sow these blocks about 15 days apart from the beginning of November and you will have ripe corn by late January through to early March.

The seed of most Sweet Corn varieties will not germinate evenly under a soil temperature of about 15 degrees Celsius,

and the cobs will not mature until the corn has experienced a minimum number of heat units.

The genetic programming of sweet corn relies on heat summation to produce a cob of corn and so the earliest varieties will usually not produce until mid to late January in Tasmania no matter how early they are put in the ground.

Be wary of the packet claims that estimate the number of days corn takes to mature.

As I have said this is determined by heat summation.

In my garden I would estimate about 2300 HU in a summer which is enough to ripen most varieties without difficulty

on plantings between November and early January.

Sow the seed at 30x30 centres about 2cm deep and water well.

Keep the bed moist throughout the germination period - about 7-10 days, and guard against snails on the emerging corn with snail bait.

sweet corn succession

The photo left shows successional plantings of sweet corn in mid December.

The plants on the right were sown in early November and the plants in the foreground are only a week out of the ground.

I usually make sowings on October 15th ( inside -seedlings planted out when they have 2 true leaves- do not disturb the roots)

November 1st, 15th, 30th

December 1st ,15th.

Jan 1st - absolutely last sowing for cool climate.

In some years you will achieve poor pollination and end up with half filled cobs,

but if you love sweet corn as much as I do you will try if you have the space.

When the plants start to tiller ( ie; grow side shoots from the base), side dress with blood and bone

to provide extra nitrogen every week or so.

Start to apply side dressing of sulphate of potash in early January to the first sowing to promote strong production of silks and pollen.

I find that Miracle is the best variety to grow in Tasmania.

It produces 2-3 nice sized cobs per plant and so over 2 weeks a dozen plants will adequately feed two people.

Sweet corn can be picked when the silks turn dark brown.

You can check the ripeness by peeling back the layers of leaves to expose the cob.

It should be picked when the colour of the kernels is cream.

Do not wait for it to go yellow as the sugar in corn turns to starch quickly and leaves a the taste of the cob chalky.

If the kernels have turned yellow, the corn is past its best.

I have had very few pests in Tasmania for sweet corn.

When I grew this in southern NSW commercially on a small scale for a couple of years,

I found that heliothis caterpillar was sometimes a problem in the developing corn cobs.

I have occasionally experienced some eating of the emergent leaves but I am unsure what has eaten them. The plants usually grow strongly after emergence because of the COF I apply.

I suggest you feed your emergent seedlings with side dressings of COF to maximise their growth and therefore minimise their susceptibility to insect attack.



When preparing ground for sweet corn, I prepare blocks for 24 plants maximum in blocks of 3 metres x1.2 metres - my normal bed width.

This allows a length of 2 rake lengths which I use to mark out my spacings. The image on left shows the spacings 30x30 which allows 3 plants across the bed and 8 plants in the length of 3 metres.

I usually prepare my sweet corn bed by planting an over wintering green manure crop which I dig in in September

leaving a month for it to rot down and leave a nitrogen ready supply for the young corn plants.

Because the green manure plants fix their own nitrogen in the soil,

the young corn plants will have plenty of nitrogen to get away to a good start.

Drop the seeds into holes of 2.5 cm depth and cover.

Water well and keep moist until the shoots emerge- about 10 days depending on temperature.


Remember that corn will not readily germinate in soil temperatures under 15 degrees centigrade.

For this reason I pre sow my first crop in punnets inside about late September.

I keep the soil warm indoors and apart from un seasonal cold snaps, the seed usually sprouts at about 10-14 days.

Once the seedlings develop true leaves , I transplant these to open spacings in the garden,

disturbing the roots as little as possible.

The early advantage of growing these plants inside is lost if there is a significant setback from the transplanting.

Bear in mind that I have already impressed that heat summation is responsible for the production of cobs,

so really early planting will not produce any real advantage.

I make 3-4 successional plantings depending on the season as outlined above.

We are usually plentiful in corn between late January and early April with gifts to neighbours and other visitors to the garden.

The success of this plant is in its feeding and the timing of its harvest.

Worth growing and fussing about to get a sensational food taste when harvested.

As soon as the cobs have been harvested, cut the stalk from the plant and chop for compost.

It is far easier to compost when the plant is green. I then fork up the roots and chop for compost.

Once your sweet corn is out of the ground, it advisable to sow a green manure crop in the Autumn months to replenish the bed with nitrogen.

This can be dug in prior to the following season when tomatoes and other Solanums plants would occupy this bed.

Sweet corn is very hungry and depletes the nutrients in its soil considerably.

A green manure crop dug in will help to replace the nutrients that have been used.

3 weeks
11 weeks
13 weeks

See Crop rotation










This page was last updated on 16/01/2018