Sow and Grow with Sara: How Cold is too Cold for Small Grains?

Spring is just around the corner and small grains will be going in soon! With the potential of continued drought-like conditions in parts of the state, and abundant water in other areas, South Dakota may have a wide planting window this spring (dependent on your region).

Many factors affect planting time, and one of the easiest to monitor is soil temperature. When temperatures start to warm up, everyone gets excited, but when should we really consider getting in the field with small grains? Spring frost is another concern with early seeding of crops like oats and spring wheat. We don’t want to see them come up and freeze off; how can we avoid this?

Although small grains are some of the most frost tolerant crops we plant, 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.

So how do we determine when 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.

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. See Table 1 for specific information on the germination temperatures of common spring-seeded South Dakota crops.

Upcoming Agronomy Events

•Private Pesticide Applicator Certification Zoom courses. If you would like to watch a Zoom rather than taking the test or participating in the training module, two dates remain: March 15 and April 6 (both run from 1:30-4:30pm CT). You must 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 on one of these two dates at the regional center nearest you, you may select that option when registering.

•Ag Economic Dialogues, March 18. Free 1-hour webinar designed to help farmers/ranchers make profitable decisions for their business. Sign up at https://extension.sdstate.edu/events.

•Forage Industry Brainstorming Session, March 29. Free meeting at the Sioux Falls Convention Center or available live virtually to discuss starting a SD Forage Association- open to everyone. Sign up at https://extension.sdstate.edu/events.

–SDSU Extension