Sow and Grow: Delayed Small Grain Planting

With late season snow blanketing much of the state, small grain planting is falling behind its typical start date. How late should we stretch cool season grain planting dates?

Many factors affect planting time, and one of the easiest to monitor is soil temperature. When soil temperatures start to warm up, it’s time to begin planting preparations. Although we will likely be behind the average planting timing this year, spring frost is still possible with crops like oats and spring wheat.

Small grains are some of the most frost tolerant crops we plant, but we still have to be mindful of soil and air temperatures when planting. The growing point on small grains does not emerge above the soil surface until jointing, after which time the crop is much more susceptible to frost damage than any time previous.

Small grains may be smarter than we think, however. Drought or several days of temperatures below 50°F can cause the plant to go through a hardening process, increasing frost tolerance. However, once the growing point emerges after jointing (when reproductive tissue is forming), the crop becomes more susceptible to frost damage, and this is when detrimental losses could occur should temperatures not cooperate.

From boot to flowering, small grains are most sensitive to frost; temperatures under 28°F will cause moderate to severe injury depending upon growth stage and length of time low temperatures are sustained. There is no hard and fast planting rule involving air temperatures and small grains, but this year’s later planting dates may help reduce the risk of plants freezing off after coming up.

So how do we determine the best window to plant small grains? Begin by monitoring 3-day average soil temperatures in the early spring. A great reference for soil temperature in your area is the SD Mesonet network. This growing weather station network measures soil temperature at five depths in several locations throughout South Dakota. Although our small grain planting depths can be quite shallow, the agricultural engineering standard for environmental observations is at a 4-inch soil depth under bare soils, making this measurement the one to rely on for planting-related soil temperature data (current agronomic recommendations take the difference in depth into account). The Mesonet site provides daily averages based on 10-minute incremental updates.

When taking a quick look at temperatures across the state this week, it is obvious that soils are still quite cool, with the majority of SD Mesonet weather stations showing the 4” bare soil temp ranging from 30-35°F as of April 5, 2023. Depending on Mother Nature’s mood, this could change relatively quickly with a spring thaw.

To check out statewide soil temperature date, visit https://climate.sdstate.edu/ and click the ‘Archive’ button at the top. From there choose ‘State Maps’ and then select the ‘Soil Temp, 4” Bare’ layer on the map; this will allow you to view the most recent data and look back at previous days as well. To view recent soil temperature data for an individual station, go to ‘Current’ and then select ‘Local Data’. Selecting a station will lead you to the current observations for that location. Once you are viewing a single station, you can choose the tab for ‘History’ to see the last seven days of measurements by choosing the ‘7-day Table’. This is sometimes easier to view for a quick overview of recent soil temperatures.

The ideal South Dakota spring planting window for grains like wheat and oats is typically accepted as the first three weeks of April or earlier if conditions are favorable. Heat and water stress can be very hard on these plants as they develop though, especially during pollination and grain fill.

If it looks like your planting date will be later than normal for cool season grains, consider an earlier variety. Doing so can help protect the stand from a mid to late summer heat wave that could negatively affect yields. With late-planted spring wheat in particular, a heavier planting rate is typically recommended to compensate for reduced tiller development.

If planting dates get significantly pushed back on your farm, it may be time to assess if a different crop could help meet your goals for the year. There is still time to meet an “ideal” small grain planting window during this first couple weeks of April, but snow pack may prevent many from achieving optimal cool-season crop planting dates.

Upcoming Agronomy Events

• Private Pesticide Applicator Certification Zoom course. The private applicator training scheduled for April 6 was rescheduled to April 19. If you would like to watch a Zoom rather than taking the test or participating in the training module, sign up prior to the event at https://extension.sdstate.edu/private-pesticide-applicator-training. If you prefer to attend a Zoom watch party in-person at the regional center nearest you, you may select that option when registering.
• Landowner Prescribed Fire Workshops- April 18-19 at Brandon. Visit the SDSU Extension Events page for details.
• Ag Economic Dialogues- 10am April 21, online. Register at the SDSU Extension Events page.
• Landowner Prescribed Fire Workshops- April 25-26 at Astoria. Visit the SDSU Extension Events page for details.

Sara Bauder is a forage field specialist with SDSU Extension.