C.O.R.N. Newsletter: 2026-16

This year, planting has been challenging due to wet weather and inadequate planting conditions across fields. The USDA shows 57% completion of soybean and 63% completion for corn planting in Ohio (week ending May 24, 2026), leaving a significant number of acres yet to be planted going into June (USDA NASS, 2026). When planting is delayed into June, there are a few agronomic practices that should be considered/changed to help minimize yield losses.

For soybeans, the management practices that can be altered with delayed plantings are: 1) row width, 2) seeding rate, and 3) relative maturity.

Row width. The row width for soybeans planted in June should be no more than 15 inches, if possible. (There may be equipment limitations.) Figure 1 demonstrates that with May planting dates, 7.5- and 15-inch rows have statistically similar yields, but 30-inch rows have significantly lower yields. As soybeans are planted later, narrow row width becomes more important. (For more information about row width, see this Science For Success FactSheet: https://resources.ipmcenters.org/resource.cfm?rid=45259&vid=30378).

Seeding rate. If you are planting soybeans in the first half of June, appropriate seeding rates are between 150,000 and 175,000 seeds per acre, with a goal of a final stand between 130,000 and 150,000 plants per acre. As planting is delayed, seeding rates should be increased to compensate, at least partially, for the shorter season.

Relative maturity. Lastly, relative maturity should be adjusted with late plantings. The maturity group that should be chosen in a late planting situation is the longest relative maturity possible that will not be killed by frost in the fall. Selecting a later maturing variety allows the plant to maximize biomass accumulation, increasing the amount of nodes where pods can form, before vegetative growth slows down after reproduction begins. If forced to plant late, adjusting to shorter maturities might be necessary, so they reach maturity before being killed by frost in the fall. Consult Table 1 (from the Ohio Agronomy Guide) to help select the most productive maturity group for your region and planting date timeframe.

For corn, the management practices that can be altered with delayed plantings are relative maturity. In the U.S. Corn Belt, full-season corn hybrids generally produce higher grain yields than short-season hybrids when planted in April and early May. The yield advantage of full-season hybrids decreases with later planting dates and may be negligible by June. Corn breeders have improved the agronomic performance of short-season hybrids by making them more competitive with the commonly grown maturities within adaptation zones. Planting early corn RM hybrids that are adapted to shorter growing seasons and earlier fall frost dates in Ohio could result in an earlier corn harvest or lower grain moisture content at maturity, which could help reduce drying costs and reductions in grain test weight.

Heat unit accumulation.  The growth of a corn plant is directly related to its accumulation of heat units over time rather than its number of calendar days from planting. Heat unit accumulation varies depending on temperature changes; it impacts corn growth and development, and subsequently, crop yields.

The corn growing degree day (GDD) system provides information for estimating crop stages and phenology (e.g., tasseling and maturity), given site-specific conditions (e.g., daily temperatures) throughout the season and planting dates. The Useful to Useful (U2U) tool helps to develop different scenarios; it provides county-level estimates based on historical GDDs accumulation, planting dates, relative hybrid maturities, GDDs to black layer, and historical freeze temperature dates (Spring and Fall). For using the U2U tool, five basic steps are needed:

1. Access the U2U online.

2. Select your location, zoom in or out as needed on the map. Search by ZIP/City/County.

3. Select the start date for GDD. As a proxy, the planting date can be used.

4. Select your corn hybrid maturity. For example, 108-day RM or 114-day RM.

5. Observe the projections: Ensure all boxes are checked in the upper-left corner of the window.

Growing degree day compression. The U2U tool assumes the same GDD is needed to reach the black layer for the same hybrid, regardless of when it is planted. Under delayed planting situations, research has suggested that GDD requirements for maturity may be reduced, which is often referred to as growing degree compression. Compression of GDD requirements to reach maturity has been observed with hybrids planted later in the season compared to the same hybrid planted under optimal time.

Research from Indiana, Michigan, and Ohio has estimated that GDD requirements from planting to kernel black layer decreased by about 3–6.5 GDD per day of delayed planting after May 1 (not always consistent across environments). This GDD compression would suggest that growers could plant their usual hybrid maturities later than expected with a lower risk of late-season frost damage. For instance, a hybrid rated at 2,800 GDDs with normal planting dates (such as late April or early May) may require 2,605 GDDs when planted on May 30. Therefore, a 30-day delay in planting may result in a hybrid maturing in 195 fewer GDDs (30 days multiplied by 6.5 GDDs per day).

For more information about Corn Relative Maturities and Yield Potential in Ohio, visit: https://agcrops.osu.edu/newsletter/corn-newsletter/2026-03/corn-relative-maturities-and-yield-potential-ohio