Is it too early to plant corn?

This is a common question every year, especially in years following an abnormally wet and/or cool spring, as has been the case the past couple of years. In three of the last four years, producers have dealt with such conditions, which either delayed planting or resulted in some plantings being "mudded" in. Because there is no way to accurately predict what the 1997 planting season will be like, producers must plan for a "normal" spring ... if we can remember what a normal spring is like.

Historically, corn was not planted in the central Corn Belt until near the first of June. This was done for two basic reasons: 1) spring plowing delayed planting, and 2) weed control was better. As fall tillage became popular and herbicides helped improve weed control, producers were able to plant corn earlier and consequential yield increases resulted. The advantages of early planting include optimized yields, drier corn in the fall, a greater choice of hybrid maturities, and a greater window of opportunity for replant decisions.

Long-term studies from the central Corn Belt indicate that yields are best for plantings made during the period from April 20 to May 5 (see table). But if conditions permit, should one begin planting before April 20? The main issues here are soil moisture, seedbed condition, and perhaps soil temperature.

Date % Yield
April 10 96
April 20 - May 5 100
May 10 97
May 20 90
June 1 81
June 10 67

Two major components necessary for germination are moisture and temperature. Soil temperature has been used as a guide for planting corn for some time. For planting corn in early to mid-April, soil temperature is still a good guide along with the short-term weather forecast, the 6- to 10-day outlook, and soil conditions. If soil moisture and temperature conditions are ideal, consider the number of days needed for planting. If the entire acreage can be planted in two or three days, it may be worthwhile to wait until the last week of April. If it takes five to seven days, then perhaps starting around April 20 would be best.

One way to estimate a "start date" for corn planting is to: 1) estimate the total number of days needed to plant, 2) add the number of "weather" days (in a normal spring, only about half of the days are suitable for field work), 3) add the number of days anticipated for mechanical or other problems, and then 4) back up the total number of days from May 5. This should give a reasonable start date that will enable planting to be completed by May 5.

On average, yields for plantings made a week or so earlier or later than the last week of April should not differ greatly, if soil conditions are desirable. Of course, there always will be exceptions to this from individual years or sites. Yield losses begin to accelerate after May 10-15. If one was to err on one side or the other of the "April 20 to May 5" window, the preference should lie on the earlier side. On average, the yield reduction experienced from planting 10 days too early will be less than that experienced from planting 10 days too late. When planting is delayed intentionally for a week, there's no guarantee that the weather won't delay it another week, or perhaps more.

Very early planting often works, but can be risky. Unless two weeks of planting days are needed, the probability of realizing significant yield increases is almost nil. Regardless of planting date, however, it's best to start on well-drained upland soils where the prior crop was soybeans. The goal should be to establish an even stand at the desired (optimum) plant population. Plant full-season hybrids first in order for them to express their full yield potential. Ultimately, getting corn planted in a timely manner and establishing a quality stand will be of greatest importance.

This article originally appeared on pages 40-41 of the IC-478 (5) -- April 21, 1997 issue.

Updated 05/23/2005 - 10:24pm