The wheat plant is a type of grass which develops over the course of a year, maturing in the summer ready for grain harvesting in late January and February. Some wheats are planted in the autumn and require a period of cold before they will form grain in late spring. Others are planted in the spring and require no cold for normal growth and grain development. In New Zealand about half the total wheat production comes from autumn plantings and half from spring plantings.
Canterbury is the major wheat producing district for both autumn and spring wheats. Autumn or spring planting is determined by climatic factors such as rainfall and environmental factors such as disease. Spring wheats generally have better bread baking qualities than autumn wheats, so end-use is also an important consideration.
Wheat plants grow several side shoots called tillers from a crown which is just below ground level. Each of these tillers grows a long stem which bears a flowering head at its top. The length of these tillers varies greatly between different wheats, some being extremely short (less than 20cm) while other are extremely tall (over 1m!). Modern wheats are generally 80cm to 1m tall.
The wheat flowers are self-fertilised by the movement of pollen from the male part of the wheat flower (stamen) to the female part (the stigma). Each flowering head fertilises its own flower. Once this has occurred the grain begins to grow and develop.
Starch and protein are stored in the grain and used as an energy source by the new plant. The grain reaches its maximum size a month after fertilisation – this is usually in mid summer. Once the grain is fully developed the wheat plant begins to die and the grain slowly dries out. It is at this stage that harvesting interrupts the growing cycle of the wheat plant, as once the grain is dry enough, the wheat is harvested. The grain is harvested by a machine (called a combine harvester) which cuts the whole plant and separates out the grain. Grain can be stored in bulk bins if the amount of moisture in the grain is kept low.