Corn

12 Jan 2022

Sweet, popping, maize
Zea mays

Corn happily grows here. It’s delicious and filling and an overabundance is easy to store. The downsides are you may have to get crafty to foil the wildlife from getting the corn before you and there is a bit of space and savvy needed to keep robust genetics in your saved corn seed over multiple generations.

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This is an ancient food plant. Corn has fed humans starchy goodness for a very long time. Our familiar yellow corn is the popular modern version. In times past, many other colours were common. Corn can be blue, white, red, pink or have kernels each of a different colour. Kernels can appear opaque or glassy.

There are a number of different types of corn. Broadly, there is sweetcorn, popping corn, and maize which is a savoury corn used as a grain. Maize is great for grinding into flours for tortillas, other flatbreads and cornflour; for polenta; and for corn grits for porridge-like dishes. There are different types of maize best suited for each of these different end uses. With all corn, the used cobs, chopped up husks and silks are good food for chooks.

The growing advice for all types and varieties of corn is the same, with some exceptions for the newly bred supersweet sweetcorns. Corn grows really well here. It’s warm enough for long enough, wet enough and not too humid. Different varieties need different lengths of growing time. Sweetcorn is picked early while immature and the husks are still green. Popping corn and maize are picked when fully mature and dry and the husks are brown.

Corn is a frost sensitive warm season plant who can be sown once soil temperatures reach 12°C, with 14 – 16°C even better. Plant from August to mid February, and you may even be able to get a couple of crops over the warm months.

Don’t plant small amounts in succession. Corn is wind pollinated and needs plenty of corn companions for successful cross pollination. Plant as many corn plants as you can, in a block, not rows, to help make sure the cobs are pollinated. Blank spaces instead of kernels on a cob means no pollination occurred for those silks. Silks are the strands that flow from the top of the corn cob. There is one silk for each potential kernel.

Sweetcorn should be ready to pick in 75 – 105 days / 11 – 15 weeks. Popcorn and maize take a little longer; 90 – 110 days or even up to 150 days / 13 – 16 weeks or even 22 weeks. Because corn is a short-day plant, some (tropical) varieties will not flower when the day length is more than 13 hours, that’s mid October to mid February here.

Mice love digging up and munching on freshly sown corn kernels. Although corn is reputed to do better when sown direct, you will need a plan for foiling the rodents. Covering the sown corn area with a mesh grill can work on a small scale. Or transplant seedlings out. Once the seed has germinated and the young plant is growing the kernel is of no interest to rodents.

Sow seeds 2cm deep. Space the plants 20 – 30 cm apart in rows 60 – 90 cm apart. Expect the mature plant to stand 1 – 2m tall. Seeds will take 4 – 12 days to germinate. Plant out when about a week old. Corn puts a lot of early energy into establishing an extensive root system and needs to be in the ground as soon as possible.

To grow corn well you will need full sun and regular water on any type of deep well drained soil. The roots can go down over a metre, so at least 50cm soil depth is recommended. pH of 5.8 to 6.5 is preferred. Corn isn’t too fussy if your soil is sandy or clay, it just demands really high fertility!

Corn needs a lot of nitrogen to grow well. It’s other main demands are phosphorus and potassium. The micronutrients molybdenum, boron, sulphur and especially zinc are also important.

The very early stages of growth and the nutrients available at that time has a permanent effect on the plant. If stunted by lack of nutrients it doesn’t usually recover. For this reason it is recommended to sow corn with plenty of food underneath, deeper than and not touching the seed, and to the side as well where the roots will grow. Blood and bone is ideal. Obviously it is wise to have prepared well in advance by enriching the soil with compost or rotted manure.

As the corn is growing give it a nitrogen based feed once the plant is about 60cm tall which should be at 30 – 40 days old. And another similar feed just before silking, at about 60 days old. Corn enjoys regular seaweed or similar foliar feeds, especially while the cobs are forming. Keep an eye out for zinc deficiency once the plant is grown. Look for a big yellow stripe down the leaves and give a zinc top up if needed.

Sweetcorn is more sensitive to moisture stress than maize, and the new supersweets even more again. In general, corn likes very even water availability. The most critical time for moisture stress is at silk emergence which is when pollination begins, after about 66 days / 9 weeks. Not enough water at this time can greatly reduce pollination. From this point in time all the way to kernel maturation there needs to be plenty of water available to the corn plant.

Pollination can also be disrupted by planting too densely, and various climate conditions; low light ie extended cloudy weather; heavy rainfall; hot (over 35°C) dry, windy weather.

Corn prefers temperatures between 15 – 32°C. Below 10°C growth stops. What it really likes is daytime temperatures of 24 to 30°C and average night temperatures around 13°C.

Corn is not fond of salt ie seaspray especially when young. Corn plants can be flattened by high wind.

While growing, corn is prone to munching attack by the corn earworm (Helicoverpa armigera). This is a caterpillar who eats the leaves and burrows beneath the husk and feasts on the ripening kernels. Look out for the small creamy oval eggs before they hatch.

More rodents! They also love corn kernels at the other end of the life cycle, when the cobs are maturing. They can decimate a patch of corn in just a few days. Again, hatch a crafty plan to foil them. This may involve traps or growing in a cage.

You may also find king parrots hanging off the maturing cobs. They love getting their beaks into fresh corn too. And wallabies like to eat the young plants. Corn is popular!

But the biggest difficulty with corn is saving enough quantity of seed with enough genetic diversity to ensure successive generations are healthy. Inbred corn will cob up later and later in the season with each generation until finally the plants fail to set seeds before winter and are killed by frost. To avoid this you need a minimum of 50 plants in a clump to maintain genetic diversity. These need to be separated by at least 500m from other varieties of corn. Ideally you only keep the cobs from the centre of the clump of plants and save about 40 cobs for seed.

Seed saving is done when the corn cobs have fully matured and dried. To kill weevils that will eat the stored seed, freeze the dried kernels for 24 – 48 hours before storing. Sweetcorn seed only keeps for a year, or two if you’re lucky in this climate. Popcorn and maize keep for 3 – 10 years. Storing kernels very dry and at a constant 5°C is recommended for maximising seed longevity.

Most sweetcorn grown is hybrid, with genetics controlled by companies and it does not grow true to type. Keeping open pollinated sweetcorn varieties going is a challenge but if the trucks stop or we have sustained supply chain interruptions, reliable corn seed will be in very short supply. If you can, save open pollinated corn seed and share it around.

Sweetcorn

Ideally sweetcorn should be eaten within 30 minutes of picking for maximum sweetness and nutrition. Fresh corn only keeps for a few days in the husk in the fridge. The sugars in sweetcorn begin turning to starch very quickly, losing sweetness. Store bought corn is usually hybrid varieties which are specially bred to be so much sweeter than the open pollinated ones and so they still taste sweet enough even when picked some time ago. Hybrid varieties are no good for saving seed to grow from next year and they don’t have the full flavour of open pollinated ones.

Pick sweetcorn when it’s still immature, while the husks are still green. All varieties of sweetcorn should do well here. Some known to have grown well here are: balinese, golden bantam, anasazi. These are all the standard sweetcorn.

There are now four types of sweetcorn: standard (su), sugary-enhanced (se) shrunken 2 (sh2), and triplesweet (sy). The su type is the familiar old-fashioned sweetcorn of the heirloom open pollinated varieties. The rest are newly bred supersweet types which taste sweeter and have a longer sweet-tasting shelf life. However as plants they are smaller, have weaker roots, are less robust against diseases, and need more exacting care. There are a very small number of supersweet open pollinated corn varieties which have recently become available.

Popping corn

Yes, it’s an actual variety of corn with the right ratios of kernel hardness, internal moisture, hard starch and oil for excellent popping. Other types of corn such as sweetcorn or flour corns generally will not pop or won’t pop particularly well. Mini popcorn is fantastic, you won’t go back to store bought popcorn after you’ve tried it according to one local fan.

Mini popcorn has a dual purpose. When picked young while the husks are still green it is cooked as ‘baby corn’. For popping, leave the husks to go brown so the kernels are completely mature and dry.

Mini popcorn comes in white, yellow, red and blue varieties. So much fun – if you can keep the mice away from the growing kernels.

Maize

This is a savoury corn best used for tortilla flour and similar cooking. It’s good to have a machine to de-kernel the cobs although this can be done by strong hands, and you will want a machine such as a corn grinder or grain mill to make decent quantities of flour or polenta or corn grits.

Leave the maize husks to go brown so the kernels are completely mature and dry for grinding. Red aztec, early leaming and manning white are varieties known to have grown well here, though any should grow well.

Big thanks to
Kaycee from The Mandarin Bend, Camilla from Autarky Farm, Paul from Barefoot Fruit & Veg.

Also to John Vernon, Tim Hill, Joy Foley, Nick Radford, John Hodgkinson, Carole & Phil Helman

Supported by Bellingen Shire Council via the Bellingen Shire Disaster Recovery and Resilience Grant Program Funding

Notes

1. Beckingham C. Sweet corn growing DPI NSW [Internet]. NSW Department of Primary Industries. 2007 [cited 2021 Dec 14]. Available from: https://www.dpi.nsw.gov.au/agriculture/horticulture/vegetables/commodity-growing-guides/sweet-corn

2. Crow R. Can Chickens Eat Corn Husks? | Don’t Waste Your Husks! – Chicken & Chicks Info [Internet]. [cited 2021 Dec 17]. Available from: https://chickenandchicksinfo.com/can-chickens-eat-corn-husks/

3. Fanton M& J. The Seed Savers Handbook. The Seed Savers’ Network; 2008.

4. Wright R, Deuter P, Napier T, Dimsey R, Duff J, Walsh B, et al. Sweet Corn Information Kit. Agrilink, your growing guide to better farming guide [Internet]. Queensland Horticulture Institute. Brisbane, Queensland: Agrilink Series QI05023. Department of Primary Industries; 2005 [cited 2021 Dec 17]. Available from: http://era.daf.qld.gov.au/id/eprint/1980/

5. Sweet corn. In: Wikipedia [Internet]. 2021 [cited 2021 Dec 14]. Available from: https://en.wikipedia.org/w/index.php?title=Sweet_corn&oldid=1042562470

6. Popcorn. In: Wikipedia [Internet]. 2021 [cited 2021 Dec 14]. Available from: https://en.wikipedia.org/w/index.php?title=Popcorn&oldid=1054214191

7. Maize. In: Wikipedia [Internet]. 2021 [cited 2021 Dec 14]. Available from: https://en.wikipedia.org/w/index.php?title=Maize&oldid=1060124203

8.Blue Mini Popcorn Seed [Internet]. Green Patch. [cited 2021 Dec 14]. Available from: https://greenpatchseeds.com.au/corn-popcorn-blue-mini.html

9. Corn seeds [Internet]. TheSeedCollection. [cited 2021 Dec 14]. Available from: https://www.theseedcollection.com.au/vegetable/corn

10. Organic Sweet Corn Production | NC State Extension Publications [Internet]. [cited 2021 Dec 17]. Available from: https://content.ces.ncsu.edu/organic-sweet-corn-production

11. Popcorn Seeds – Succeed Heirlooms Australia [Internet]. Succeed Heirlooms. [cited 2021 Dec 14]. Available from: https://www.succeedheirlooms.com.au/heirloom-vegetable-seed/heirloom-corn-maize-seeds/maize-popcorn.html

12. Organic Vegetable Seeds Online – Corn to Cucumber [Internet]. [cited 2022 Jan 15]. Available from: https://greenharvest.com.au/SeedOrganic/VegetableSeeds/CornToCucumber.html