Growing Degree Days and Planting Decisions for Corn

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Based on past growing degree information for Delaware (https://sites.udel.edu/agronomy/2022/06/22/average-delaware-growing-degree-days-2019-2021/) corn emergence may occur anywhere from 84-150 GDD, with an average of 109 GDD. A more nationally recognized value for corn emergence is about 120 GDD for 50% of your stand.

With warmer temperatures over the next few weeks, some planting has already started, and may see reduced stands if cooler temperatures and wet soils prevail. In 2022 (Figure 1a), planting April 15^th did not obtain enough growing degree days over a two-week period to reach emergence, particularly in the northern end of the state. Sussex county didn’t reach 109-120 days until around May 4^th. Even planting on April 25^th did not result in 109-120 GDD within two weeks (Figure 1c), which is when we typically start at our Georgetown research farm.

Statewide in 2022, a May 1^st planting was when we accumulated enough growing degrees statewide (Figure 1d), although the coastline during that time remained cooler. Remember that these are air temperatures, and soil temperatures rise and fall slower. For 2023, the slightly warmer weather looks conducive to earlier planting if you are willing to risk some stand loss and later emergence. However, this can rapidly change, so choose fields with good drainage and limited residue/cover to enhance soil temperatures and emergence.

Figure 1. Accumulated growing degree days in 2022 based on a) April 15^th-30^th, b) April 15^th– May 4^th, c) April 25^th– May 9^th, and d) May 1^st to May 15^th.