A good starting point for seeding canola is when the three-day average soil temperature in the seed zone is 4-5°C. This is the temperature where biological activity typically begins.
By early May, soil temperature at 1” depth — the canola seed zone — often exceeds this temperature during the day and should get continually warmer with each day. For this reason, soil temperature in May is less of a factor in the seeding-start decision than it would be in April.
To determine the average soil temperature: Use a soil thermometer and take readings at 8:00 a.m. and 4:30 p.m. over a few days and average the results. Because canola is seeded at 1” deep, test the soil temperature at that depth. Be consistent. With a probe-style thermometer, one tip is to dig a small hole and insert the thermometer horizontally at seed depth. This makes sure the reading is based on the correct soil depth. You may also want push in the temperature to record deeper temperatures. This provides a soil temperature less prone to flucation and adds background on soil temperature trends.
If a probe thermometer is too slow for your liking, consider an infrared thermometer — available at most hardware stores. You need to dig down to the target zone, but once there, the thermometer reading is instantaneous. A digital contact probe thermometer is pretty quick, too.
Alberta growers can use the Alberta Agriculture Agroclimatic Information Service website to see the soil temperature at numerous locations across the province. Checking the site earlier this week, it seems that northeast Alberta has the coolest soils at 2-3°C but this should jump to 7-8°C by later in the week — given the forecast. The rest of the province was already at 6-12°C and should keep getting warmer as well.