Sweetcorn or maize (Zea mays), is likely to be the only cereal crop that the general kitchen gardener will grow. It is a grass, and consequently wind pollinated. Generally, it is a low maintenance crop once established, and can be grown successfully outdoors or under cover. Sweetcorn grows a long stem, which, depending upon variety, is typically five to eight feet tall. Our polytunnel crop this year has grown rather taller than the same variety grown outdoors in the two preceding years. The stem bears some resemblance to bamboo; leaves grow from each node, and the cobs form between leaf and stem several nodes up the stem. Depending upon planting density, one plant can support several cobs, and I would expect to get, on average, 1½ well formed cobs per plant.
In terms of pollination, the first sign to watch out for is the developing ‘tassels’ that form at the top of the stem. This is the pollen producing part of the plant. As these begin to grow, the young, unfertilised, cobs will be visible further down the stem. Each cob will develop a bundle of ‘silks’ at their tip. Even for the first time grower of sweetcorn, these will probably be familiar as being something of a nuisance when removing the husks for cooking. The cob is actually quite remarkable; each thread of the silks is attached to one potential kernel, and must be pollinated for that kernel to develop. Poor pollination, then, leads to partially filled cobs.
As the tassels spread out, the dangling pollen filled anthers will, with but a little encouragement, begin to drop their pollen down onto the waiting silks below. Outdoors, a gentle breeze is usually sufficient to achieve good pollination. This explains why sweetcorn is typically planted in a block rather than a row. When growing under cover, or outdoors if the weather is cool or damp, or in still conditions, a little help might be in order. Usually, an occasional shake of the stems over the course of a couple of weeks, will suffice. One can go further and remove part of one of the tassels, and gently rub over the silks, though I have not yet found this to be necessary. It should be noted that the second and any further cobs will form a little later than the first, so it is worth being a bit careful not to shake or otherwise remove all of the pollen until all of the silks have developed.