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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Corn planted on different dates in 2016 at the NWIARDC. From Left to right is corn planted on April 5, April 15, May 5 and May 19.

Planting date and corn and soybean development

Corn and soybean planting date trials. Each year corn and soybean planting date trials are established at the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC) in Monmouth. Sunshine, adequate moisture and moderate temperatures are needed to drive the enzymatic reactions responsible for plant growth and development.

Relationship between temperature and corn growth. The relationship between temperature and corn growth has long been studied. Corn plants require heat (between 50 and 86 °F) in order to grow, develop and reach vegetative and reproductive milestones on their way to physiological maturity. Growing degree days are a measure of the accumulated heat and associated corn growth and development during the growing season. Chapter 2 in the Illinois Agronomy Handbook has a good description of daily GDD calculations and the number of GDD that typically must accumulate in order for corn to reach specific growth stages.

Corn development and projected flowering and maturity dates. Corn planted on April 5 and April 15 (likely considered a little early and timely, respectively) has developed ten and nine leaf collars, respectively, and is projected to reach silking and black layer within a day of one another. Development and projected silking and black layer milestones are delayed in corn planted on May 5 and 15 (Table). Visually, corn planted on April 5 is chest high while May 19 planted corn is knee high (Figure). Corn planted each date appears to be healthy and is absent both insect injury and foliar disease symptoms.

Table. Current (June 14) and projected developmental milestones for a corn hybrid (110 day maturity) planted on different dates at the NWIARDC in 2016. Accumulated growing degree days, projected silking and black layer dates were collected from the Corn GDD – Decision Support Tool produced by the Useful to Usable project.

As of June 14

Projected Milestone Dates

Planting Date

Accumulated GDD

Growth Stage


Black Layer

April 5



July 6

September 9

April 15



July 7

September 10

May 5



July 15

September 22

May 19



July 21

October 4

Soybean development on June 14. Soybeans planted on April 18, May 7 and May 19 have six, four and three trifoliate leaves, respectively (Table). According to the Illinois Agronomy Handbook,

"If temperatures are close to normal, planting date affects the length of time required for soybeans to mature, with delays resulting in fewer days needed for the plant to complete its life cycle. The period from planting to the beginning of flowering is typically 45 to 60 days for full-season varieties planted at the normal time. This interval is shortened as planting is delayed; it may be only about 25 days when such varieties are planted in late June or early July, but this also means that plants may be small and canopy may be less than adequate when flowering starts. A rule of thumb is that for each 2- to 3-day delay in planting, plants reach maturity one day later. The lengths of the flowering and pod-filling periods also are shortened, but the effect of late planting on these phases of development is minor."

In time, we will be able to see any effect of planting date on beginning flowering and yield.

Table. Current (June 14) developmental milestones for a soybean variety (3.4 maturity) planted on different dates at the NWIARDC in 2016.

Planting Date

Growth Stage

Days since planting

April 18


57 days

May 7


38 days

May 19


26 days

June 7


7 days

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