Canola is one of the world’s most widely grown oilseed crops, selectively bred from rapeseed to have low levels of erucic acid and glucosinolates. It is a significant commodity, providing high-quality vegetable oil for human consumption and a protein-rich meal for animal feed.
The plant is best known for the dramatic visual transformation it brings to agricultural fields when it reaches its reproductive stage. When canola enters its flowering period, fields turn into a brilliant sea of bright yellow blossoms. This bloom signals that the crop is entering its most sensitive period for determining final yield.
General Timing of the Canola Bloom
The timing of the bloom depends on the type grown, but for spring-planted crops in the Northern Hemisphere, flowering occurs between late spring and early summer. In major North American production areas, flowering typically starts in May and continues into June. The onset of this stage follows the rapid stem elongation phase, known as bolting.
The flowering process is indeterminate; the plant continues to produce new flowers at the top of the stem while lower flowers transition into seed pods. This allows the plant to sustain production, which can help compensate for short periods of environmental stress. The duration of the full field bloom generally lasts between two to four weeks, with three to five new flowers opening on the main stem each day.
The visual peak of the bloom occurs when the field reaches approximately 50% flowering, where half of the flowers on the main stem are open. After this point, the field begins to appear less intensely yellow as older petals fall off and the flower production slows. The end of the bloom signals that the plant is shifting its energy focus entirely to the development and filling of the seeds within the newly formed pods.
Key Variables That Shift Bloom Dates
The spring-to-summer timeline is highly variable due to two distinct commercial types: spring canola and winter canola. Spring canola is planted in early spring, matures quickly, and dominates colder regions. Winter canola is planted in the autumn, develops leaves before winter, and requires vernalization (a period of cold temperatures) to trigger its reproductive stage.
The winter variety flowers much earlier, often reaching full bloom in warmer regions by the second or third week of April. This difference in planting and life cycle means the crop can bloom months apart depending on the cultivar and geography. The timing of flowering is tracked using accumulated heat units, known as Growing Degree Days (GDD).
GDD models help predict the developmental stage based on ambient temperature, using a base temperature below which growth is negligible. For many spring canola varieties, flowering begins once the plant has accumulated approximately 506 to 567 GDD on the Celsius scale after emergence. This heat accumulation requirement explains why warmer weather accelerates the bloom.
Significance of the Flowering Stage
The flowering stage is when the plant transitions from vegetative growth to reproductive output. Each flower must be successfully pollinated to develop into a silique, the long, thin seed pod that contains the seeds. A healthy bloom directly correlates with the number of pods and seeds per pod, which are the main components of final yield.
While canola is largely self-pollinating, the presence of insect pollinators, especially honeybees and wild bees, is beneficial. Pollination encourages more uniform flowering and leads to earlier pod-setting. Studies show that bee pollination can increase yields by a significant margin, from 5% to 20%, and can also increase the weight of the seeds.
The flowering period is also when the crop is most vulnerable to environmental stress, such as heat and drought. High temperatures can cause flower abortion, where the plant sheds its blossoms before forming a pod. Successful flowering and early pod development maximize the plant’s reproductive capacity before the final seed-filling stage.