The best corn crops in Ontario and Quebec are usually planted in late April and the first half of May because the crop is able to utilize the full growing season.
IMPACTS OF PLANTING DATES AND SOIL TEMPERATURES
The optimum corn planting date in southwestern Ontario is on or before May 7, and on or before May 10 in central and eastern Ontario/western Quebec. Delaying planting past the optimum date can result in yield reductions averaging about 1% per day of delay in May. As planting dates become later, the rate of yield loss per day of delay increases. Yield losses for the first three weeks of June are about 2% per day of delay in longer season regions (>3,050 CHU) and 3% per day of delay in shorter season regions. (Source: Ontario Ministry of Agriculture, Food and Rural Affairs)
It is generally necessary to start planting corn well before the optimum plant date, depending on how many days are required to plant all the corn acres. Be sure soil temperatures reach a minimum of 10°C – required before germination and emergence will occur – when planting earlier than the optimum dates. If average soil temperatures are at or beyond 10°C, the soil conditions are favourable and the weather forecast is predicting average to above-average temperatures, then early planting of at least a portion of the corn crop is recommended.
After April 26 (May 1 in areas receiving <3,000 CHU), corn planting should be a priority. It is advisable to pay less attention to soil temperature and plant as soil moisture conditions permit. Generally, the loss of potential yield associated with planting 2-3 weeks before optimum planting date is less than the loss associated with planting 2-3 weeks after the optimum planting date. (Source: Ontario Ministry of Agriculture, Food and Rural Affairs)
APPROACHING OR PASSING OPTIMUM CORN PLANTING DATES
Plant full season hybrids first. Prioritize hybrid maturities when looking at which hybrids to plant first. Plant the fullest season, latest flowering corn hybrids first since these hybrids take the longest to reach black layer.
The planting order should be:
Do not work soil if it is too wet. Compaction can be a major problem in cool wet years, and will reduce yields more than a delay in planting of a few days.
Plant for a uniform stand. Do not increase planting speed – this will result in poorer stands and planting problems. If conditions indicate a prolonged cool wet period after planting, many producers want to increase planting populations 5-10% to compensate for potential emergence problems and seedling diseases.
Plant first before it gets too late. Nitrogen can be side dressed until the 8-leaf stage. Post-emergent herbicide can be substituted for pre-plant and pre-emergent herbicides if needed. It is more important to get corn planted than to stick to an original plan and miss the optimum planting window, if alternatives are available.
Change hybrid selection. If planting delays become excessive, consider changing hybrid selection. These are some general guidelines that vary depending on the area.