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When is it ‘Too Late’ for Planting Spring Oats, Spring Barley, and Spring Wheat?

 

by
Chaunce Stanton, Marketing Manager
Margaret Smith, PhD, Forage Agronomist

 

The key to a successful grain harvest of spring-planted oats, barley, or spring wheat is to promote tillering and head formation — growth phases that occur during relatively cool temperatures. Air and soil temperatures matter more than calendar date when it comes to a successful small grain harvest.

Understanding the Growth Stages of Cereal Grains

Cool-season annuals, spring-planted cereal grains thrive in temperatures below 70-75o F. Minimum soil temperature for germination of small grains are 35-37o F for spring wheat and barley, and 37-40 º F oats. Ideally, for germination and early growth, daytime air temperature highs would reach 60 º F and overnight temperatures would not drop below 40 º F for a robust stand within eight to 10 days after planting. Fortunately, during seedling emergence, the plant crown can sustain temperatures down to at least 28 º F. Once germinated, the plant is now programmed for development – there is no return to dormancy.

Cereal grains pass through two development stages: the first, vegetative stage sets the foundation for crop development by forming a rosette of initial leaf growth from the root crown and by initiating tillers. Each tiller can develop an additional stem complete with its own leaves, roots and tillers, and seedhead, capable of producing grain. The number of tillers is reduced when planting is delayed. High temperatures in the later spring result in more rapid accumulation of Growing Degree Days (GDD), limiting the time for tiller development.

After cereals complete this early growth stage, and sufficiently long days (hours of sunlight per day) are reached, they enter their second, reproductive stage. To reproduce (produce seed) the plant's main stem elongates, seedheads form, followed by head emergence, flowering and seed development.

The yield potential of small grains is established by the 6-leaf stage of crop development. To allow the potential for high grain yields, a plant must produce the most viable flowers/florets that can become harvestable grain. These flowers develop from the spikelets, and the number of spikelets that develop are directly affected by temperature. Cooler weather during flower initiation and pollination causes rye/oat/wheat/barley plants to increase the number of kernels at each spikelet.

Following pollination, cooler temperatures during grain fill extend the number of days available for photosynthesis and carbohydrate transfer to each grain. thereby increasing the test weight of each kernel. Both the main stem and tillers have the potential to form loose panicles (as in oats) or spikes (as in wheat and barley) that will flower and then proceed to grain fill.

Recommended Spring Planting for Small Grains

But how late can you plant spring small grains for a good grain harvest? Clearly, conditions differ from year to year, and, of course, each state's planting ranges can vary by areas even within that state (north to south, for example). Here's an example from the University of Minnesota Extension's Optimum and Latest Planting Dates for Spring Small Grains in Minnesota.

We've collected a smattering of links for Midwest states, and, although this is a work in progress, we hope to build out a more comprehensive collection of information.

Illinois

Minnesota

Nebraska

North Dakota

South Dakota

Effects of Delayed Planting on Cereal Grain Development

With delayed planting, average temperatures tend to increase, speeding cereal grain crop development. Crop plants move through their growth stages more quickly – often at the cost of potential yield. Early warmth promotes plant growth, but unusually high temperatures can stress the plant. Growing too quickly means that plants produce fewer tillers, develop smaller heads, and result in smaller kernels and lower test weight. Additionally, if plants lack adequate moisture in summer heat, they will preserve water by closing their stomata, reducing photosynthesis, which also is detrimental to yield.

As an example, oats in the Upper Midwest generally are planted in early April and harvested in mid-July, but wet spring weather can delay planting and push the grain fill stage into the hottest part of the growing season with high temperatures posing a potential threat to grain yield. Several days of temperatures above 75°F during head emergence through the milk stage reduces yields.

Remember 2018! Late Planting and then Hot

Using 2018 as an example, planting was delayed with April snow with temperatures dipping well below freezing, then jumping into the 80s and 90s at the end of May. The hot weather continued into June, coupled with substantial rainfall. These conditions significantly reduced overall yield as wheat, barley, oats, and rye (all long-day plants) flowered, set seed, and matured quickly as the summer heat hit early.

On average, late-planted cereal grain yields decrease 1 percent every day past the optimum planting date.

In addition, due to more rapid GDD accumulation, fewer days are available for plants to photosynthesize and translocate carbohydrates to filling grains. As a result, the protein level (relative to carbohydrates) increases in grain harvested after late planting, which can be especially problematic for farmers growing barley for malting.

"I'm Planting Oats, Barley, or Wheat Late: What Will Help?"

You may want to consider an alternative crop instead of risking a poor (or failed) small grain harvest. But if you must plant late, increase the seeding rate by 1 to 1.5 percent for every day past the optimum planting date, up to 1.6 million seeds per acre. Since tillering will be reduced with warmer temperatures, the increased seeding rate will promote more main stem development to help overcome tillering loss, but summer heat stress is likely to affect final test weight, even in a thickly planted stand.


RESOURCES

Development of the Oat Panicle (USDA)

Oats (Purdue)

Planting Small Grains (University of Minnesota Extension)

Small Grains Field Guide (University of Minnesota Extension)

Soil Temperatures and Spring Planting Dates (University of Nebraska - Lincoln Extension)

Temperature Thresholds and Crop Production: A review (New South Wales Department of Industry and Investment)

Tillering in Wheat (Wageningen University & Research)

Usual Planting and Harvesting Dates for U.S. Field Crops (USDA)

Why is My Rye Short? (Albert Lea Seed)

Winter Wheat Production Manual (University of Saskatchewan)

Fine-Tune Oat Seeding Rate this Spring (Iowa State University)

Delayed Planting May Increase Rust and Yellow Dwarf in Oats (Iowa State University)

Plant Oats Early to Avoid Disease (Iowa State University)

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