Corn Planting: Timing, Soil Temperature and Stands
Posted: April 23, 2013
In practical terms, the ideal corn planting time is typically only a few days long. In most years, each day’s delay past this period reduces yields up to 1 bushel per acre per day. Consequently, corn planting should begin early enough to ensure that the bulk of the crop can be planted during this optimum period. Normally, corn can be planted safely 10 to 14 days before the average date of the last killing frost.
In the coldest areas of Pennsylvania, the optimum dates for Zone 1 (85-99 RM) are May 15 to 25, while in part of the west and central areas of our state the optimum dates for Zone 2 (100-108 RM) are May 1 to 15. In the extreme southwestern areas of PA, along with a narrow band along Lake Erie and southern areas of the ridge and valley region the optimum dates for Zone 3 (109-114 RM) are April 25 to May 7. Only in southeastern PA do the optimum dates for Zone 4 (115+ RM) run earlier, from April 15 to May 1. The Penn State Agronomy Guide uses a map the PA corn maturity zones.
Regardless of soil temperature, before planting corn be sure that the soil conditions will support equipment without causing severing compaction problems. It’s never a good idea to “mud it in.” If soil conditions permit planting, then a combination of soil temperature and calendar date should be used to determine when to plant. Essentially, a good guideline to follow is to plant according to the soil thermometer very early in the season, but as the normal or optimal planting period approaches, soil temperature should become less of a priority.
When planting early, consider using the following guidelines:
- Measure soil temperature at corn planting depth (1.5 to 2 inches). If the early morning temperature (the low) is above 50 degrees (F), then consider planting. Check the forecast for assurances that the soil temperature of 50 degrees (F) or above is likely to hold for 3-5 days.
- It is recommended to measure soil temperature in the same type of soil as you will plant into. Also, it is best to measure soil temperature in the same type of tillage, crop residue, or cover crop system. A very useful resource available through our web-page on the left column PA Pest Information Plantform (PA PIPE) includes Daily Minimum 2-inch Soil Temperatures. Currently 2-inch minimum soil temperatures (readings taken just before daybreak) are apparently below 40 degrees F for most of the state. Producers BEWARE!
- Consider increasing seeding rates by 2,000 kernels per acre when planting very early in cold and wet soil due to erratic stands typically observed under these conditions. Stand may not be a problem if the soil is cool and dry.
In general, corn should be planted when soil temperatures are near 50 °F. Seed will absorb about 30 percent of its weight in water, and temperature does not affect this process much. However, this is different than radicle (root) and coleoptile (shoot) growth; their growth is correlated with soil temperature. In cold soil conditions (below 50 °F), seeds will readily absorb water but not initiate root or shoot growth; this leads to seed rots and poor emergence if poor seedbed conditions are prolonged. Cool, wet conditions predispose seedlings to infection by a number of fungi that cause seedling disease, and can result in seedling damage and/or death. Survival of young corn seedlings depends on a healthy kernel and mesocotyl, which should remain firm and white throughout to at least growth stage V6.