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Late planting spring small grains

Wheat, barley and oats are cool season annuals that are most productive when they grow and develop during cool weather.

The crop’s yield potential is largely determined by 6-leaf stage. Cool temperatures during this period are particularly important to develop high yield potential. For example, the number of tillers that ultimately produce grain at harvest declines as planting is delayed (Figure 1).

The number of spikelets per spike is determined during the 4- to 5.5-leaf stage (Figure 2). Spikelet numbers are negatively correlated with temperature; you get more spikelets per spike when temperatures during the 4- to 5.5-leaf stages are cool.

graph showing affece of planting date on number of wheat heads per square foot
Figure 1: How planting date affects the number of heads per square foot of hard spring wheat at harvest in Langdon, North Dakota.
line graph showing affect of temperatre on wheat spiklets per spike
Figure 2: How maximum daily temperature affects spikelets per spike initiated between spring wheat’s 4- and 5.5-leaf stages.

Crop development

The higher average temperatures expected with late planting will speed up a crop’s development. Heat units accumulate faster, pushing the crop to the next phase of development.

This forces the crop to develop faster and gives plants less time to grow. Plants end up with fewer tillers, smaller heads and fewer and smaller kernels per head, which ultimately cuts into yields.

To improve the odds of high grain yields, plant early to ensure the tillering and head initiation phases occur during relatively cool temperatures (Table 1).

Planting dates: Optimum and last

Table 1: Average seeding dates and last recommended seeding dates for small grains in Minnesota

Minnesota Optimum seeding date Last planting date
South of U.S. Highway 12 First week of April First week of May
South of Minnesota Highway 210 Second week of April Second week of May
Second week of May Third week of April Third week of May
South of U.S. Highway 2 Fourth week of April Fourth week of May
South of Canadian border First week of May First week of June

Research has shown that, on average, yields decreased 1 percent per day when planting is delayed past the optimum planting date. Planting after the last possible date is not recommended because grain yield and quality (test weight) will likely be dramatically reduced due to heat stress.

You can partially offset this yield loss by increasing the seeding rate and ensuring you have more main stems per unit area. Increase the seeding rate by 1 percent for every day after the optimum planting window.

Adjusting the planting date

The last possible date for planting is not set in stone. The chances of a profitable crop only drop because of the weather and temperatures expected later in the growing season. If you’ve passed the last possible date, consider an alternative crop, though economically feasible.

If you stay with small grains past that date, you’ll have to hope for a cool and dry summer. For example, summer 2013 weather conditions were so favorable that, despite the late planting date, Minnesota’s average hard red spring wheat (HRSW) yield was the third highest ever reported. This was largely the result of cooler nighttime temperatures.

Scatter chart showing the difference in daily minimum temperatures differences in the 2012 and 2013 growing seasons in Devils Lake, North Dakota
Figure 3: Daily minimum temperatures differences in the 2012 and 2013 growing seasons in Devils Lake, North Dakota. Day 56 is around when grain fill begins.

Jochum Wiersma, Extension agronomist

Reviewed in 2018

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