Maize has 11 separate growth stages, numbered 0 to 10. Growth stage 0 lasts from planting the seed up to when the seedling is just visible above the soil surface. Growth stage 10 is when the plant is biologically mature.
Growth stage 0: from planting to seed emergence
During germination, the stem and growth point are 25mm to 40mm below the soil surface. In warm, moist conditions seedlings emerge after six to 10 days; under cool or dry conditions, this may take two weeks or longer. The optimal temperature range for germination is between 20°C and 30°C, while the optimal moisture content of the soil is approximately 60% of soil capacity.
Growth stage 1: four leaves completely unfolded
The maximum number of leaves and lateral shoots is predetermined and a new leaf unfolds every third day or so. The growth
point at this stage is still below the soil surface and aerial parts are limited to the leaf sheath and blades. Tasselling starts at this stage.
Growth stage 2: eight leaves completely unfolded
During this period, leaf area increases five to 10 times, while stem mass increases 50 to 100 times. Ear initiation has already commenced. Tillers develop from nodes below the soil surface. Growth at this stage is 5cm to 7,5cm above the soil surface.
Growth stage 3: 12 leaves completely unfolded
The tassel in the growth point begins to develop rapidly, as do lateral shoots bearing cobs from the sixth to eighth nodes above the soil surface. The potential number of seed buds of the ear has already been determined.
Growth stage 4: 16 leaves completely unfolded
The stem lengthens rapidly and the tassel is almost fully developed. Silks develop and lengthen from the base of the upper ear.
Growth stage 5: silk appearance and pollen shedding
All leaves are completely unfolded and the tassel has been visible for two to three days. The lateral shoot bearing the main ear and bracts has almost reached maturity. Demand for nutrients and water is high.
Growth stage 6: green mealie stage
The ear, lateral shoot and bracts are fully developed and starch begins to build up in the endosperm.
Growth stage 7: soft dough stage
Grain mass continues to increase and sugars are converted into starch.
Growth stage 8: hard dough stage
Sugars in the kernel disappear rapidly. Starch accumulates in the crown of the kernel and extends downwards.
Growth stage 9: physiological maturity
When the kernel has reached its maximum dry mass, a layer of black cells develops at the kernel base. Grains are physiologically mature and only the moisture content must be reduced.
Growth stage 10: drying of kernels (biological maturity)
Although grains have reached physiological maturity, they must dry out before reaching biological maturity. Under favourable conditions, this takes place at about 5% per week up to the 20% level, after which there is a slowdown.
Source: Du Plessis, Jean: Maize Production (department of agriculture).
