Temperature of soil prior to seeding
The optimum soil temperatures for most spring seeded crops are warmer than 10°C. Planting all crops at lower soil temperatures will delay emergence.
Various crops, however, will germinate at various ranges of soil temperatures.
- Peas and lentils are quite cold tolerant. They can be planted when the average soil at the depth of seeding reaches five degrees Celsius (5°C).
- Desi chickpea can also start to germinate at about 5°C.
- However, large kabuli chickpea, dry bean and soybean do not germinate and emerge well at these cool temperatures. Kabuli chickpea, dry bean and soybean should not be planted until the average soil temperature at the depth of seeding reaches 10°C.
- Canola and mustard - will germinate at temperatures as low as 2°C.
- Flax - can germinate at temperatures as low as 3°C or 4°C.
- Cereal crops - wheat and barley are also quite cold tolerant and can be seeded at about 4°C to 5°C.
Measuring soil temperature
Determine how deep you will be placing the seed. Then place your thermometer at the depth of seeding. Take two measurements throughout the day: one in the morning and one in the early evening. Average the two readings to determine average soil temperature at depth of seeding. Take readings in a number of locations in the field, especially if the field is rolling and variable.
Which crop should I seed first if I am concerned about a spring Frost?
There is no definitive answer. Different crops have different susceptibilities.
The growing point for cereals such as wheat, oats and barley is below the soil surface until the plant has advanced past the three leaf stage. Therefore, wheat, oats and barley can withstand quite severe frost damage in the early part of the season.
Peas and lentils can germinate at lower temperatures and take a little longer to absorb sufficient moisture and so could be an early seeding choice. Peas and faba beans are more cold tolerant than lentils. Pulse crops can regrow after a light frost.
Canola, mustard and flax are often seeded earlier in May to encourage flowering earlier in the season. This early seeding limits the crop's exposure to high temperatures often associated with mid-summer. Canola, mustard and flax are very susceptible to frost at the cotyledon stage. However, once they have passed the two-leaf stage and have been hardened by exposure to colder temperatures, they can withstand freezing temperatures for short periods of time.