Corn has two distinct phases of growth: vegetative and reproductive.
Vegetative Growth Stages in Corn
Vegetative stages are identified by the number of collars present on the plant. The leaf collar method is
generally used for staging vegetative (V) development of corn. When corn seedlings emerge from the soil and no
leaf collars have formed, plants are in the VE stage. When the plant has one visible leaf collar, it is in the V1
stage. The leaf collar is a light-colored band located at the base of an exposed leaf blade, near the spot where
the leaf blade meets the stem of the plant. Leaves within the whorl, not fully expanded and with no visible leaf
collar, are not included in the staging. For example, a plant with three collars would be called a V3 plant;
however, there may be five to six leaves showing on the plant (Figure 1). Corn plants generally develop up to the
V18 stage before reaching maximum height at tassel emergence (VT) and transitioning into the reproductive (R)
stages of growth.
Beginning at about V6, the lowest leaves may fall from the plant and dissection of the lower stalk may be
necessary to accurately stage the plant. To stage older plants, dig up the plant and split the stalk down into the
root ball. Find the triangular “woody” base of the stalk and locate the first internode above the base. The woody,
horizontal node is the point of attachment for the fifth leaf or collar. For example, if you can count five
visible leaf collars above this point, the corn plant is in the V10 growth stage.
Figure 1. Corn growth stages from emergence to maturity.
||Can occur four to five days after planting under ideal conditions, but up to two weeks or longer under
cool or dry conditions.
||At V1, round-tipped leaf on first collar appears, nodal roots elongate. By V2, plant is 2 to 4 inches
tall and relies on the energy in the seed. V3 begins two to four weeks after VE, and plant switches from
kernel reserves to photosynthesis and nodal roots begin to take over. Around V4, broadleaf weeds should
be controlled to avoid loss. By V5, the number of potential leaf and ear shoots are determined. Plant is
8 to 12 inches tall and growing point remains below soil surface.
||Beginning four to six weeks after VE, the growing point grows above the soil surface, increasing
susceptibility to hail, frost, or wind damage. The nodal root system is dominant. At V7, rapid growth
phase and stem elongation begin. Number of kernel rows is determined and potential kernels per row begins
and continues through V15/16. By V8, the plant reaches 60 cm (24 inches) tall.
||Around six to eight weeks after VE, corn begins steady and rapid period of growth and dry matter
accumulation. At V9, tassel is developing rapidly, but is not yet visible. New leaves appear every two to
three days and ear shoots are developing.
||By V12, the plant is about 4 feet tall or more. Nutrients and water are in high demand to meet growth
needs. All leaves are full size and roughly half are exposed to sunlight. Brace roots are developing and
the potential number of kernels per ear and size of the ear are still being determined. Insect and hail
injury can reduce the number of kernels that develop. The plant is about two weeks away from silking at
V15. The tassel is near full size, but not visible. Moisture and nutrient deficiencies at this time can
reduce the number of potential kernels per row resulting in shorter ears and lower yield potential.
||Beginning around nine to ten weeks after emergence, corn enters a critical period where successful
pollination is required to convert potential kernels into viable, developing kernels. The plant has
reached full size. Tassels are fully visible, and silks will emerge in two to three days. Pollen shed
begins and continues for one to two weeks. Hail can be very damaging at this stage.
Reproductive Growth Stages in Corn
Corn plants enter reproductive growth after completing tassel emergence. Reproductive growth stages are determined
by kernel development and not plant collars.
Figure 2. Corn kernel fill during reproductive stages.
Corn Growth Stages
Figure 3. Kernel at black layer, note the darkened tip indicating that full kernel maturity has
||Silking is one of the most critical stages in determining yield potential. A plant has reached R1 when
the silks are visible. For a field to be in the R1 stage, the average silking date is used. The average
silking date is when 50% of the plants have started to silk. Pollination begins at the base and proceeds
toward the tip. Physiological maturity can be estimated by adding 50 to 55 days to the silking date.
||About 12 days after silking, silks darken and dry out. Kernels are white and form a small blister
containing clear fluid. Each kernel develops an embryo. Kernels contain 85% moisture. Stress (especially
drought) at this stage can reduce yield potential by causing kernel abortion.
||About 20 days after silking, kernels are yellow and clear fluid turns milky white as starch accumulates.
Kernels contain 80% moisture. The effects of stress are not as severe after this stage, but can still
result in shallow kernels, stalk cannibalization, or lodging.
||About 26 days after silking, the starchy liquid inside the kernels has a dough-like consistency. Kernels
contain about 70% moisture, begin to dent at the top, and have accumulated close to 50% of their maximum
dry weight. Stress can produce unfilled or shallow kernels and “chaffy” ears.
||About 38 days after silking, nearly all kernels are dented and contain about 55% moisture. Cob has
distinct color: white, pink or red. Silage harvest begins sometime during this stage, depending on
desired whole plant moisture.
|R6 Black Layer
||About 60 days after silking, physiological maturity is reached, and kernels have attained maximum dry
weight at 30 to 35% moisture. Total yield is determined, and frost has no impact on yield.
Crop Heat Units (CHU)
In Canada, Crop Heat Units (CHU) are used to describe how heat accumulation is calculated each season. This is
Always refer to each seed company on how hybrids are rated as relating to maturity and CHU accumulation. Some seed
companies do not include the 150 CHU needed from germination to emergence in their maturity rating.
Our seed guide refers to the CHU accumulation needed to hit Black Layer (physiological maturity) for a corn hybrid
in grain corn production.
For silage or grazing purposes, you can generally select a hybrid that is 150-200 CHU higher maturity rating than
your normal accumulation in your growing area. This is due to the fact that silage corn does not have to reach
full physiological maturity.
CHU is based on air temperature. CHU is calculated for each day and is accumulated when air temperature is above
4.4oC and below 30oC. Air temperature must reach 12.8oC for three consecutive days before CHUs begin accumulating.
When -2oC is reached, CHU accumulation ends.1
Heat unit maps are generated by Agriculture and Agri-Food Canada and can be found here.2
1Manitoba Agriculture and Resource Development. Agriculture Climate of Manitoba. https://www.gov.mb.ca/agriculture/weather/agricultural-climate-of-mb.html.
2Agriculture and Agri-Food Canada. Agroclimate Interactive Maps. https://www.agr.gc.ca/atlas/agclimate.
Performance may vary from location to location and from year to year, as local growing, soil and weather
conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and
should consider the impacts of these conditions on the grower’s fields.
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