Corn – improving pollination

All types of corn are pollinated by breezes that blow pollen from the male flowers onto the silk threads that emerge from the top of each ear of corn. This is why it is better for home gardeners to grow corn in a block rather than a long row. Each strand of silk is connected to a separate immature seed and is covered in tiny sticky hairs that collect the pollen. If some silk strands don’t receive pollen, kernels may not form along one side of a cob, or near the top of the cob. (Female part of corn plant in photo at left.)

Male flowers form at the top of the corn plant as an upright spike and lower branches that open out like umbrella spokes. Pollen forms in small yellow ovals (anthers) that release their pollen mid morning after dew has dried from the flowers (between about 9 and 11 am). The centre spike is the first part to release its pollen. Pollen release may only last from 3 to 5 days and the released pollen is only viable for up to 24 hours. (Male flower in photo at left.)
It can help when growing small quantities of sweet corn or popcorn to pollinate it by hand, to ensure that the cobs your plants produce are full of juicy kernels. In nature, silks are rarely pollinated by the same plant.

To ensure good pollination, you need a sheet of A4 paper and a clean, dry, soft paintbrush. Fold the paper in half lengthways and open it out, then fold it in half the opposite way and open it out. This helps the paper to form a shallow well. Or, you can use a small clean shallow tray – something easy to manoeuvre between the plants. Hold the paper under a male flower and gently tap the spike and lower branches of the male flower with the handle of the paint brush. When tassels are ready to be pollinated, plenty of bright yellow pollen will fall onto the paper. Collect some of the pollen on the hairs of the paintbrush and dab it onto all sides and the centre of silk strands of other corn plants. Repeat this process over several days. Once a tassel has been pollinated, the ends of the silk strands will start to turn brown. As the cobs mature, you may have to net your corn crop as birds know when corn is perfect for eating.
Corn anthers won’t release pollen when conditions are too wet or very dry, the plants will wait until conditions are favourable. In areas of Australia that experience long periods of rain, it is best to plan your corn crop to avoid the wet season.

Growing popcorn

corn.jpgFoods made from genetically engineered (GE) crops, also known as genetically modified (GM) foods, are not required to be labelled in the United States, and Australian consumers of imported corn products could unknowingly be eating these foods. Labelling rules for GE/GM foods set by Food Standards Australia New Zealand (FSANZ) fail to protect consumers as they allow many exceptions to labelling of GE/GM foods and ingredients, and rely heavily on the honesty of producers and processors to inform the public of the genetically engineered content of the food they buy. There is no post-marketing assessment of foods to ensure compliance with GE/GM labelling regulations.
If your family is fond of eating popcorn, and you wish to avoid GM foods, why not grow your own popcorn this summer.

Update – 16/11/2013
The first step is to buy popcorn seed, which is becoming extremely difficult to find. Gardeners in QLD, NSW, VIC and the NT can order organically-certified seed from:
Green Harvest –  ‘Popcorn’, although the variety being sold this year is a hybrid which means that you won’t be able to save some seed for next year’s crop. It appears that ‘Golf Ball’, ‘Ontos’, ‘Ruby’, ‘Blue Mini’ and ‘Strawberry Mini’ have already disappeared from the market.
Popcorn is made from a particular ancient variety of corn whose kernels (seeds) contain air pockets. When the dried kernels are heated, the air in the kernels expands and the seed “pops” open. Plants that produce popcorn may have several stems and carry multiple small cobs, instead of the usual two large cobs per plant of many other corn varieties.
Popcorn is grown in the same way as sweet corn, as it is also a heavy feeder. It needs a sunny position and well-drained soil that has had plenty of organic matter added in the form of compost or well-rotted manures, plus an application of complete organic fertiliser. All varieties of corn do well if grown after a green manure crop – a point to remember for next year. Because corn relies on wind drift for pollination, small quantities of corn are best grown in a block rather than rows. If you are growing other varieties of corn, allow at least a month between sowing popcorn and the other varieties because they can cross-pollinate.

Sowing seed:
Corn requires a soil temperature of 20° C for germination. Popcorn can be sown from August North of Rockhampton, and from September in other warm areas. Other areas can begin sowing in October. Popcorn takes a little under 4 months to reach maturity.
Seed is sown directly into a mulched bed. Space planting holes 40-45 cm apart, and sow two seeds, 3 cm deep, in each hole. Traditionally, popcorn is sown during First Quarter moon phase.
When seedlings have developed their second set of leaves, thin them to the strongest seedling at each position, and give the seedlings a drink of manure tea. When plants are knee high, hill them up about 15 cm encourage extra roots to form, and to make the plants more stable in windy conditions. Corn requires regular irrigation until cobs mature, and it more likely to attract corn earworm if water is in short supply.

Pollination:
Corn plants produce separate male and female flowers. The male flowers that produce pollen are shaped like ears of wheat at the top of the plant. Another drink of manure tea, and a drink of seaweed tea can be applied when the male flowers start to form.
The female “flowers” are the green silk tassels that protrude from the cob sheath. Each strand of the tassel is attached to a single kernel on the cob and poor pollination occurs when wind is absent and pollen only falls onto one side of the tassel. In still conditions, you may have to flop the tassels around, or transfer pollen with a dry paintbrush to ensure that all the silk strands are pollinated.

Harvesting popcorn:
Popcorn cobs remain on the plants past the harvesting stage for sweet corn, to allow the seeds to fully mature. As soon as tassels have browned, the plants should be netted, as birds know exactly when corn is perfect for eating. When the husk, or sheath, of the cobs has begun to dry and is changing to a pale cream colour, the corn is close to maturity. If weather is fine, cobs can be left on the plants until the sheaths are completely dry, or they can be brought indoors at this point to complete drying. We leave them on racks indoors for several days, then carefully peel back the husks, thread wool or string through the turned-back husks, tie the string to form a loop, and hang the cobs from a hook until the seeds are completely dry about 14 days after the husks have dried. Kernels can be left on the cob or shucked by rubbing two cobs together over a large bowl. It is recommended that the kernels be transferred to a sealed plastic container and frozen for two days to kill any weevil eggs that made have been laid in the seeds. After freezing, transfer the popcorn to a screw-top jar, and pop as required.