How to Determine Corn Growth Stages

Corn has two distinct phases of growth: vegetative and reproductive.

Vegetative Corn Growth Stages

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. 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.

Leaves within the whorl, those not fully expanded and with no visible leaf collar, are not included in the staging. For example, the plant pictured in Figure 1 is in the V3 stage because it has three leaf collars, even though five leaves have emerged. The two leaves that lack a visible leaf collar are not counted for the purposes of staging the plant.

Corn plants generally develop up to the V18 stage—or up to V21 depending on the genetic background and relative maturity of the corn product—and then transition into the reproductive (R) stages of growth before reaching maximum height at about R2 (Figure 2).

Beginning at about V6, the lowest leaves may fall off and dissection of the lower stalk may be necessary to accurately stage the plant. To stage older plants that have lost leaves, dig up the plant and split the stalk down into the root ball. Find the triangular-shaped base of the stalk and locate the first noticeably elongated internode above the base, which is typically about one-half inch long. That horizontal node is the point of attachment for the fifth leaf and can be combined with the visible leaf collars to stage the plant. For example, if five visible leaf collars are counted above this point, the corn plant is in the V10 growth stage.

Estimating Corn Growth Stage with Growing Degree Days

Corn growth stages can also be estimated using corn growing degree days (GDDs) accumulated daily from the date of planting. The formula for calculating corn GDDs is written out in Figure 3. Briefly, corn GDDs are calculated by taking the maximum daily temperature in Fahrenheit^† (Max Temp) plus the minimum daily temperature in Fahrenheit (Min Temp) and dividing this number by two, which gives the average temperature in a 24-hour period. A base temperature of 50 °F (Base Temp) is then subtracted from the average temperature to calculate the number of corn GDDs accumulated in that 24-hour period.

^†Note that corn development slows drastically when the temperature is above 86 °F, so 86 should be used as the Max Temp for calculating corn GDDs any time the maximum daily temperature exceeds 86 °F.

Corn plants require various amounts of GDDs at various stages of vegetative development. Corn usually requires:

• 100 to 120 GDDs to emerge after planting
• 82 to 85 GDDs to complete each leaf collar from emergence through the V10 growth stage
• 50 to 55 additional GDDs for each collar emergence in later vegetative stages after V10

Here is an example of using GDDs to estimate the vegetative growth stage of a corn plant:

Step 1 – Using the formula in Figure 3, a grower calculates that a field has accumulated 380 GDDs from the date of planting.

Step 2 – The grower subtracts the number of GDDs the plants needed for emergence (120) from the total GDDs accumulated (380), 380 − 120 = 260.

Step 3 – The grower divides the remaining GDDs (260) by 82, the number of GDDs usually required for the plant to complete each leaf collar to the V10 stage. This allows the grower to estimate that the corn plants are in the V3 growth stage, 260 ÷ 82 = 3.17.¹

While corn GDD can be used to estimate growth stage, keep in mind that the exact number of GDDs needed for a corn plant to develop can vary, and that stress factors (especially drought) can influence growth rate. Therefore, the GDD calculation may not provide an accurate estimation of growth stage.

A corn GDD tool is available at High Plains Research Climate Center, https://hprcc.unl.edu/agroclimate/gdd.php that can help track GDD and estimate corn maturity based on historical temperature data.

The Vegetative Growth Stages (V) of Corn

The GDD estimates below are based on a corn product that produces a total of 20 leaves, which requires 2,700 GDD to black layer, and had a normal planting date.

VE – Corn Emergence

This stage may occur four to five days after planting under ideal conditions, but may require up to two weeks or longer under cool, wet, or dry conditions. After planting, about 100 to 120 growing degree days (GDDs) are required for emergence. Photosynthesis begins at this stage, and the radicle and seminal roots are growing.

V1 Corn – First Leaf Collar

The first leaf with a collar is rounded or oval-shaped at the tip, while any subsequently developed leaf will have a pointed tip. The first ring of nodal roots are developing at this stage. Damage to the mesocotyl will result in seedling death.²

V2 Corn – Second Leaf Collar

The plant is relying on energy from the seed. Seminal roots have reached their maximum size and nodal roots continue to develop.² About 200 GDDs have accumulated.

V3 Corn – Third Leaf Collar

The seed is no longer contributing to growth, so the plant is now relying on photosynthesis for energy. Root hairs are now visible on nodal roots.²

V4 Corn

At the V4 stage, control of grass and broadleaf weeds is critical to avoid significant yield loss (GDD = 360).³

V5 Corn

Plant height is about eight to 12 inches tall, and the growing point is still below ground. The number of potential leaves and ear shoots are being determined.²

V6 Corn

The growing point is now above the soil surface, increasing the plant’s susceptibility to hail, frost, or wind damage. The nodal root system is dominant. Development of all leaves, ear shoots, and the tassel has been initiated and any potential tillers are beginning to develop (GDD = 520).²

V7 Corn

The number of kernel rows around the cob has been fixed by this growth stage. The plant begins to determine the number of kernels per row (ear length), which continues through the V15 to V16 growth stages.²

V8 to V9 Corn

Plants are entering a rapid growth phase both above and below ground. All ear shoots that were initiated are now visible with dissection, which can be as many as eight (usually on nodes six to 14). Tassel development is occurring, and the brace roots begin to develop. Plant height is about 36 inches and potential kernels begin to develop at the base of the ear, progressing toward the tip (GDD = 680 to 760).²

V10 to V11 Corn

A new leaf emerges every two to three days, and rapid uptake of nutrients and moisture is occurring. Rapid growth can cause corn plants to become vulnerable to greensnap until the VT growth stage.²

V12 Corn

By V12, the corn plant has accumulated close to 10% of its total dry matter (DM). Nutrients and water are in high demand. All leaves are now formed and about half are exposed to sunlight. Brace roots continue to develop. Tassel and ear shoots are easily found with dissection of the plant (GDD = 900).²

V13 to V16 Corn

By the V13 to V16 growth stages, the number of kernels per row has been determined or is nearing final determination. Nutrient deficiencies, injury from hail, or drought and heat stress at this time can lower yield potential. A V15 plant is about two weeks from silking and has accumulated about 25% of total DM (GDD = 955 [V13] to 1,150 [V16]).²

V17+ Corn

The plant is becoming increasingly vulnerable to yield loss due to hail damage or moisture stress as it approaches the VT to R1 growth stages (GDU = 1,300).²

VT to Corn Tasseling

Tasseling occurs two to three days prior to silking, with pollen shed lasting about four to six days for an individual tassel. The plant has taken up about 65% of the total nitrogen (N), 50% of the total phosphorus (P), and 85% of the total potassium (K) it will require for the entire season.⁴ Hail can be very damaging at this stage (GDD = 1,350).

The Reproductive Corn Growth Stages (R)

Corn plants enter reproductive growth after completing tassel emergence. Reproductive growth stages are determined by kernel development, not by plant collars.

R1 – Silking

Silking is one of the most critical stages in determining yield potential. An individual plant is considered to be in the silking stage once the silks are visible. A field is determined to be in the R1 growth stage based on the average silking date. The average silking date is when 50% of the plants in the field have started to silk.

Pollination begins at the base and proceeds toward the tip. Potassium uptake is complete, and nitrogen and phosphorus uptake is occurring rapidly. At this stage, leaf analysis for nutrients is highly correlated with final yield.² Physiological maturity should be achieved 50 to 55 days after the average silking day (GDD = 1,500).

R2 – Blister

About 10 to 14 days after silking, silks darken and dry out. Kernels are white and form a small blister containing clear fluid (Figure 4). Each kernel develops an embryo. Kernels contain 85% moisture. Stress (especially from drought) at this stage can reduce yield potential by causing kernel abortion. The plant has reached maximum height, and the translocation of nutrients from the stalk to the ear begins (GDD = 1,700).²

R3 – Milk

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 aborted kernels, shallow kernels, stalk cannibalization, or lodging (GDD = 1875).

R4 – Dough

About 26 to 30 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 lower test weight (GDD = 1,950).²

R5 – Dent

About 38 to 42 days after silking, nearly all kernels are dented and contain about 55 to 60% moisture. Cob color is now discernible. The milk line separating the soft, milky part of the kernel (closest to the cob) from the starchy portion is distinct. By half milk line, about 90% of dry matter (DM) accumulation has occurred (GDD = 2,300).²

R6 – Black Layer

Black layer, or physiological maturity (PM), is reached about 55 days after silking. The black layer is formed at the base of the kernel (Figure 5). All dry matter has accumulated and final yield has been determined. The kernels are at about 30 to 35% moisture content (GDD = 2,700).²