There are three systems in common use for scheduling sweet corn plantings. All are relatively simple and require little in specialized equipment. They differ considerably, however, in their ability to avoid wasted corn from bunching of harvests in hot weather.
The most widely used system is to just go out every few days and plant some corn. It takes little time and requires no special equipment. Its accuracy improves some with experience but, on most farms, it results in some corn being passed over because two or three plantings all matured at the same time.
The second system uses the days to harvest published in the seed catalogs. With this system, several varieties are chosen that mature at three-day or four-day intervals. As soon as soil temperatures reach 500F, plantings of all varieties are made. Then a chart is developed to plan the next planting so that the earliest maturing variety in the second planting matures three or four days after the latest variety in the first planting. The system is then repeated until you reach the last planting date for your region.
This system usually assures a continuous supply of corn but still suffers from bunching of harvests. In addition, the more different seed catalogs you use, the more likely the system is to fail. This system requires an hour or two to make the chart and only a pencil, paper and a soil thermometer for equipment.
Scheduling sweet corn plantings using the Growing Degree Days (GDD) or heat unit method is a simple way to assure a continual supply of sweet corn without the bunching of harvest that sometimes occurs. To use the GDD system, you need to know five things: (1) The supply of sweet corn you will need; (2) the average GDD in the anticipated harvest period; (3) the GDD required to mature the sweet corn varieties you are growing; (4) the maximum and minimum temperature each day during the planting season; and (5) the base temperature for sweet corn (50°F).
Let’s work through a simple example. Suppose you want to harvest 350 bags of corn per day, seven days a week. If we assume a yield of 14,000 ears per acre, we must plant 1-1/2 acres per planting to yield 350 bags (21,000 ears).
We plan to make several plantings of a variety with GDD to maturity (available from the seed supplier) of 1,302. The minimum temperature at which sweet corn grows is 50°F. Therefore, our first planting can be made when the soil temperature reaches 50°F. Beginning the day after planting, record maximum and minimum temperature for each day and calculate the GDD using a formula:
GDD = ((Maximum Temperature + Minimum Temperature)/2) -50° F
In Storrs, Connecticut, a sweet corn variety requiring 1302 GDD to maturity planted April 19 would be expected to mature about August 1. The average GDD per day around August 1 (calculated from weather records) is 19. If we want to pick the field for three days, then 3 x the average degree days (19) or 57 GDD must accumulate before the next planting.
To recap our example of GDD scheduling:
- Make the first planting when soil temperature reaches 50°F.
- Estimate the time of harvest and calculate average GDD per day in the harvest period.
- Determine the number of days you plan to harvest the planting (three in our example).
- Calculate the GDD that will accumulate during the harvest period (3 days x 19 GDD/days) = 57.
- Record maximum and minimum temperatures and calculate.
GDD = ((Maximum Temperature + Minimum Temperature)/2) -50° F
- Add daily GDD from planting until they equal the GDD in the intended harvest period (57).
- When GDD equal those in the harvest period, make the next planting.
- The process can be repeated for subsequent plantings and other varieties.
To obtain specific variety GDD information, contact your seed supplier.
The GDD system requires about six to eight hours per season, a soil thermometer and a maximum/minimum thermometer in addition to the pencil and paper needed for the previous system. The advantage gained is the best chance of avoiding wasted sweet corn caused by several plantings maturing at the same time.
The use of GDD also offers the best chance of avoiding skips in harvest caused by summer cold spells.
The variation in growing degree-days is always greater in the spring than in the summer. For example, say you are planting in late April for harvest in late July. The anticipated growing degree-days in July are 21 per day. You are planning to pick the planting for three days. At planting you record the high temperature of 62°F, the low of 48°F and calculate the growing degree-days (GDD) as 62 + 48 = 110÷2 = 55-50 = 5 GDD. If you are planning to pick for three days, 63 GDD must be accumulated before the next planting (2 1×3). At this rate, 12 or 13 days would pass before the next planting.
Now suppose the temperatures were running 5° below normal. The high would be 57, the low 43 and the GDD 57+43=100÷2=50-50=0. Planting would be delayed until the cold spell passed or bunching of harvests would occur.
Now consider the situation at harvest. You are anticipating 21 GDD per day at harvest. The high might be 82°F, the low 60°, and the GDD 82 + 60= 142 ÷ 2=71-50=21. What if we had a cold spell in August? If it was 5° colder than normal, the high would be 77°F, the low 55°, and the GDD 77 +55 = 132 ÷2 =66 -50 = 16. This represents a delay in maturity of about six hours. The cold spell would have to continue for four days to delay harvest one day and stretch two weeks before a gap developed.
Growing degree-days are your best bet to schedule sweet corn plantings to avoid both bunching and gaps of harvests.
Also see article: Scheduling Sweet Corn Plantings — The Anderson Farm Way
By: Richard A. Ashley, University of Connecticut, Cooperative Extension Specialist, Vegetable Crops
Originally published: New England Vegetable & Berry Growers Conference Proceedings. 1997. p. 119-12
Reviewed by: T. Jude Boucher, IPM, University of Connecticut. 2012
This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.