Seed as early as soil conditions permit. Canola will germinate and grow at soil temperatures of 2°C, but 10°C is ideal for rapid emergence. Sustained low soil temperatures have a detrimental effect on the seed embryo. Soil conditions and weather forecasts should guide your decision , however 5°C or higher is a reasonable target for planting. At 6°C, emergence reaches 100% within 8 days. When seedlings emerge, the growing point is exposed between the cotyledon leaves (seed leaves). Canola seedlings can withstand a considerable frost of -5°C to -8°C if plants have become acclimatized following a few days of cold temperatures. However, canola seedlings growing under warm conditions will be tender, and can be killed by a light frost. Canola seedlings on muck soils are at a greater risk of frost injury. Increasing seeding rates by 5%–10% when canola is planted very early will help to compensate for slower emergence and increased seedling mortality.
Early April seeded canola has higher risk of mortality from seedling disease, soil crusting, and flea beetles. Early planted canola also has a higher risk of infestation by cabbage seedpod weevil during the flowering/early pod stage. Be prepared to control flea beetles if canola is slow to develop beyond the susceptible stage (i.e., up to 4 true leaves).
In the past it has been recommended to seed before mid-May to reduce the risk of damage by swede midge. To avoid significant swede midge damage, the goal is to have the canola bolt prior to swede midge emergence in late May to early June. However, experience in Northern Ontario has shown that seeding early sometimes results in slower emergence and growth and may not mitigate swede midge damage.
If seeding is delayed, it is critical to conserve soil moisture and to plant into moisture for rapid, uniform emergence. Shallow planted, small canola seedlings die easily when they run out of soil moisture. Late seeded canola is at risk of flowering during higher temperatures which can reduce yield and carries risk of challenges with later maturity and harvest.