Growth Rate and Days to Maturity
Canola development is aligned with growing degree days (GDD) and the amount of sunlight captured. Canola grows best at temperatures between 10°C and 30°C, with an optimum of 18°C to 25°C. The average crop flowers 45 to 50 days (582–666 GDD) after emergence and matures in 90 to 96 days. Northern growing areas such as New Liskeard receive less GDD, but this is partially offset by longer daylight hours. The average number of days to maturity is 10 to 14 days longer in northern areas than western Ontario. The approximate GDD to reach various stages of development are presented in Table 1.
Table 1. Approximate growing degree days to reach various stages of spring canola development
| Growth Stage (decimal code system) | Description | Growing Degree Days (Base 0ºC)1 |
| 0–1.0 | emergence | 152–186 |
| 1.0 | cotyledons unfolded | |
| 1.1–1.2 | 1–2-leaf stage | 282–324 |
| 1.4–1.6 | 4–6-leaf stage | 411–463 |
| 2.0–2.2 | bolting — internode lengthening | |
| 3.0–3.9 | bud development | 582–666 |
| 4.0–4.9 | flowering— 20% of all buds on main raceme flowering or flowered | 759–852 |
| 5.1–5.9 | pod development | 855–1,400 |
| 6.0–7.9 | seed development | |
| 8.1–8.4 | ripening and maturity2 swathing stage | 1,432–1,557 |
| Legend: Decimal indicates number of leaves exposed. 1 Adapted using research data from Agriculture and Agri-Food Canada (AAFC), Scott and Swift Current. 2 Occurs when seed begins to mature, 10% seed colour change. | ||
Maturity differences among varieties are typically less than 7 days. When canola planting date is delayed, plants adjust by growing more rapidly through the vegetative stages in response to higher temperatures that are typically present. As a general guide, a 1-week delay in planting will delay maturity by 3 days. High temperatures (i.e., above 28°C) at flowering cause flower and pod abortion and have a significant impact on yield. Drought and heat stress will shorten the days to reach maturity.
Root System
Canola has a large main taproot that can extend up to 1.5 m (4.9 ft) deep into the soil under favourable growing conditions. Despite its taproot, canola is not capable of penetrating a soil hard pan and is susceptible to soil compaction. About 70% of the canola root system is in the top 15 cm (6 in.) of the soil profile. Early season root growth has a strong positive relationship to final yield. During early vegetative growth, moist topsoil and dry subsoil will result in a shallow root system. Canola roots will not grow in search of water or nutrients, they only intercept water or nutrients present in the soil. Soil compaction, weed competition, or dry soil can limit root growth and make potential canola yields more dependent on timely rainfall during flowering and pod fill. Root growth peaks at flowering.
Plant Development
Germination of canola is similar to other dicots. Emergence generally occurs between 4 and 15 days after planting, depending on soil and climatic conditions. The small seed will only sustain growth for approximately 7 days before accessing nutrients from the soil or through photosynthesis. Canola seedling mortality can be high unless quick, uniform emergence occurs. At emergence the seedlings are very small, and the root will be approximately 3–5 cm (1.2–2 in.) long. The growing point of canola is located between cotyledon leaves (seed leaves) and is susceptible to frost, insect and slug feeding and hail damage. The first true leaf appears about 4–8 days after emergence. Leaf area development is directly related to growth rate and final yield. Rate of growth depends on many environmental factors including soil temperature, air temperature, moisture, photoperiod, fertility, and pest feeding. Establishment and growth up to the 4-leaf stage may be slower than weed growth, making canola seedlings a poor competitor with weeds.
Canola develops a rosette with older leaves growing large at the base and new, smaller leaves forming at the center. Leaves are waxy and hairless. Canola will produce anywhere from 9 to 30 leaves. Achieving and maintaining a high leaf area is associated with higher yield. Lengthening days and rising temperatures in the spring trigger bud formation in the center of the rosette quickly followed by stem elongation (“bolting”). If conditions are extremely dry during the early rosette stages, the stress may cause canola to bolt early.
Secondary branches develop from growing points in leaf axils along the main stem. At typical spring canola plant populations, plants will have 3 to 7 branches. At lower plant populations, canola will produce a thicker main stalk and branch more profusely. The increased branching results in plants flowering over a longer period and taking longer to fully mature. The stems and branches continue to elongate through flowering.
At the onset of flowering, the main stem will be 30-60% of its maximum height. Final height is influenced by cultivar, fertility, moisture and population. Canola typically reaches between 100 and 175 cm tall (39 to 69 in.). The main stem will reach maximum height around the same time as peak flowering. The stem is an important source of photosynthate during pod and seed fill.
Flowering
Flowering begins with the opening of the lowest bud on the main stem and continues upward on both main and secondary branches as they elongate. The first flower to open, and therefore the first pod to form, is at the bottom of the main stem. The last flowers to open are at the tips of the branches. Individual flowers remain receptive to pollination for 3 days after opening, and flowering continues for 14–21 days.
The bloom stage at a given time is typically described by how far through bloom the crop has progressed as a percentage, where halfway through the bloom period is referred to as 50% bloom. The bloom stage is approximated based on a visual assessment of the crop. There are approximately 10 flowers open on the main stem at 10% bloom, 20 flowers open on the main stem at 30% bloom, and greater than 20 on the main stem plus some on side branches at 50% bloom. Canola can progress from first flower to 30% bloom in 6 to 10 days.
Canola produces more buds than can be developed into pods, and abortion of flowers and pods is normal. Canola is primarily self-pollinated but can cross-pollinate, depending on various environmental factors. Fertilization occurs within 24 hours of pollination. Temperature stress (>28°C) during this period causes flower abortion and is detrimental to yield.
Ripening
Pods contain two rows of seeds, separated by a thin membrane. Seed filling is complete 30–40 days after flowering. Pod ripening starts from the bottom of the plant. When seeds have turned green, leaf senescence begins, and the pod wall becomes the major source of photosynthate, although the stem is also important. Firm, green seeds are physiologically mature and are capable of germinating and supporting seedling growth. Temperature or drought stress during pod development can cause pod abortion.
Seed from mature Argentine varieties (Brassica napus) has a brown to black seed coat colour and are yellow inside. Seed colour change begins at the bottom of the plant and progresses up the main stem as moisture content decreases. When 30–40% of seed on the main stem has started to change seed coat colour, overall moisture content will be around 30%-35% and the seeds in the last formed pods are completing filling. Seed colour change advances by about 10% every 2–3 days; the rate increases in hot weather and may decrease in cool weather. The colour of the pod when seeds are mature will vary depending on the variety and environment, so the pod or plant colour visible across the field is not a good indication of seed maturity or moisture content. Fully mature pods may shatter and lose seed.