Time of Seeding

Table of contents

    Important tips for best management

    • Early-seeded canola crops tend to produce higher yield and quality. These crops tend to flower before peak summer heat, which can lead to flower blast and pod abortion, and maturing earlier often helps mitigate damage from frost in the fall or other stresses that cause premature senescence.
    • Cold soil temperatures following seeding can delay emergence and increase seedling mortality, sometimes offsetting the benefits of earlier planting. Canola seeded into 2 °C soils can germinate, but may take up to 3 weeks to reach 50% emergence if temperatures remain cool. Waiting for somewhat warmer soils may allow establishment of a denser more uniform stand that matures more evenly and can be harvested earlier, but consider the calendar and long range forecast. Soil temperatures of 5 °C or higher with warmer weather in the forecast should facilitate reasonably good rates of emergence, but from the second week of May onward growers should probably take advantage of good field conditions for seeding regardless of temperatures.
    • Because canola emerges more slowly in cold soils, protection from seed treatments may decline before the crop has outgrown its most susceptible phase. With early seeded canola, be ready to apply an insecticide to control early season flea beetles. Earlier control of weeds may also be necessary, especially for perennials and winter annuals that are better adapted for growing under cold conditions.
    • Seeding into cold soils increases the need for management techniques that reduce stress on emerging seedlings such as seeding shallow, some seed placed phosphate to get the “pop up effect,” uniform seed placement, early weed control, and proper crop residue management to allow the soil to warm as quickly as possible. Growers may want to increase seeding rate to offset the potential for lower seed survival in cool soils.

    Yield trends

    The yield advantage for early seeding — with all else being equal — can be significant. [1] [2] [3] [4] [5] [6] Seeding early, providing that crop conditions allow for it, is a relatively low cost way to increase yield and profit from the crop. 

    In general, “early” seeding occurs from late April to mid May but varies by region. In the southern Prairies, early seeding usually allows the crop to utilize winter and early spring moisture more effectively and may help the crop avoid the highest summer temperatures during flowering. Early season moisture from snow melt can be critical to facilitate the shallow seed placement required for maximum emergence and good seedling establishment and growth. Missing this early season moisture forces the crop to rely more heavily on subsequent rains throughout the season. 

    Optimum canola seeding dates in Ontario are usually in late April to early May — slightly earlier than western Canada. Significant yield reductions occur if seeding is delayed after mid-May, mostly because the crop is flowering during the hot and frequently dry weather in late June and July.

    By seeding some fields early, this maximizes the amount of acres seeded in the proper seeding date window  — rather than having a large amount of acres seeded at the end of the seeding window. In most areas in western Canada, seeding after the third week of May puts canola at higher risk for fall frost losses.

    Early seeding increases the risk of stand loss due to lethal spring frosts, but canola seedlings that are slow growing and have hardened off can withstand some early season frost. Early seeding can decrease the risk of yield and quality loss due to fall frost damage. Seeding early may actually reduce the overall frost risk since spring stands severely damaged by frost still have ample time to recover or to be reseeded.

    If soil temperatures are cold during seeding, then other seeding practices (treated seed, pedigreed seed, good seed-soil contact, proper fertilizer placement, correct seeding depth and rate) become even more important.

    Keep in mind that canola emerges more slowly in cold soils, which means protection provided by seed treatments can decline before the crop has outgrown its most susceptible phase. With early seeded canola, be ready to apply an insecticide to control early season flea beetles. Slow growing canola crops will also be more vulnerable at the seedling stage to weed competition. Earlier control of weeds may be necessary, especially for perennials and winter annuals that are better adapted for growing under cold conditions, and hence more able to compete with the crop under those conditions.

    Seeding date is often dictated by factors outside the grower’s control. These include:

    • The field has to be able to support tractor traffic. This depends on the amount of snow and runoff, soil texture, spring precipitation and temperature, slope, and residue. As well, the field has to be dry enough to ensure the canola is not “mudded in”. The field may support the tractor and drill, but soil does not fill in properly over the furrow and packers mud up and slide. Seed placement and seed to soil contact suffer, resulting in inconsistent seed depth and uneven emergence.
    • Pre-seed herbicide applications to control winter annuals and cool-season weeds may push back seeding dates, especially since growers want to make sure weather is warm to ensure good herbicide uptake. When seeding without pre-seed weed control, a post seeding/pre-emergent or early in-crop application will be necessary.


    Seeding date selection - soil temperature considerations

    Soil temperature is a significant influence on the rate of canola germination and emergence. Canola can germinate at temperatures as low as 2-3 °C, but germination rates are lower and slower, with seeds germinating over a period of weeks. At 6 °C, close to 100% germination can occur within 8 days. [9]

    Figure 1. Influence of Soil Temperature on the Rate of Canola Germination B. Napus

    Seeding based on soil temperature alone is not a good idea. Soils may be warm and workable in late March or early April in some regions some years, only to face a month-long cold snap and a foot of snow. Before seeding, consider the probability of severe or sustained cold weather after seeding.

    Figure 2. Influence of Soil Temperature on the Rate of Canola Germination B. Rapa

    Figure 2. Influence of Soil Temperature on the Rate of Canola Germination B. Rapa

    On the other hand, if soil temperatures are only 1 °C in early May and weather is predicted to stay cool, some growers may decide to seed anyway because good seeding days can be rare some years and by early May you expect warm temperatures soon. Other growers will hold out for warmer soils, knowing canola will emerge more rapidly and vigorously. However, by mid May or later, growers should probably take advantage of good field conditions to get canola in the ground regardless of soil temperature. By that time, chances are good that soil temperatures will warm up following planting even if they are cold at the time of seeding, and the greatest yield penalties from planting late have typically resulted from seeding in last week of May or early June.


    Seeding in April

    Seeding in late April is fairly common in the Brown and Dark Brown soil zones, and has been tried in Black and Grey Wooded zones. April-seeded canola faces higher risks from early insect infestations, seedling disease pressures, water ponding, soil crusting, frost damage, and slow emergence due to cold soil. But under the right conditions, seeding in late April can provide an added yield benefit over May seeding. [5]

    April-seeded canola will have higher seedling mortality but the plants that survive will have more time to branch out and compensate for a thinner stand. April seeded canola should target 150 seeds per metre square or higher to maximize potential of reaching adequate plant stands.

    Fall seeding

    Canola seeded in early spring yields as well as or better than fall seeded canola (spring type canola seed planted late enough in fall that cold soil prevents germination until the following spring). [5] [7] With the high value of canola seed, growers are less inclined to take a risk on fall seeding when early spring seeding provides similar or superior yield potential. Fall seeding of canola in Western Canada is not a recommended practice.

    Crop insurance for spring canola varieties seeded in the fall is available only after inspection in the spring. If the crop is established to the satisfaction of the provincial insurance provider, the crop can be insured as though it were a spring seeded crop. Winterkill coverage is not available in Alberta, Saskatchewan or Manitoba.

    Winter canola seeded in the fall is common practice among canola growers in southern Ontario, but the winter hardiness of these varieties is still inadequate for use on the prairies. Fall seeding of spring varieties is risky, even in southern Ontario. Any warm temperatures after seeding may lead to premature germination of dormant seeded canola. Spring freeze and thaw cycles can also greatly reduce seed soundness and germination rates. Growers may want to increase the seeding rate — maybe even double the rate — to attempt to compensate for the high risk seed environment.

    If considering fall seeding:

    • Avoid fields with many low spots that flood in spring or windswept slopes with insufficient residue.
    • Avoid summerfallow or heavily fall worked fields, which tend to have more spring crusting problems that will reduce emergence. They also tend to trap less snow and have earlier snow melt, leading to earlier germination and emergence in spring and greater potential for spring frost damage.
    • Try it on small fields first, or split a field to allow comparison to spring seeding under similar field conditions.
    • Seed just prior to freeze-up.
    • Seed to soil contact must be obtained, and try to retain surface residue to prevent spring crusting. However, the residue must be spread evenly.
    • Seed shallow at one to 2 cm (roughly 0.5" to 0.75") and avoid leaving furrows that fill in over winter, increasing the actual seed depth.
    • Avoid broadcasting seed, which tends to increase mortality on the surface. Use typical rates of good quality seed. Fall banding of the fertilizer usually provides the best efficiency and yield response. 


    Not all canola can be seeded the first weeks of May due to crop conditions or logistics of a large farm operation. With late May or early June seeding, the risk of fall frost halting maturity and reducing yield and quality rises, as does the risk of flower blast during the heat of summer. But canola seeded late May or early June seeded canola can still produce good quality and yields under favorable conditions.

    Seed shallow and conserve moisture to ensure rapid emergence of a dense and uniform stand — which will minimize days to maturity. Keep in mind that later seeding tends to reduce the rated days to maturity for a canola variety, as illustrated in Table 2 with research from Edmonton, Alta., and Brandon, Man. This reduction in maturity is often about half of the delay in seeding. For example, if seeding is 14 days later than optimal, a variety rated to mature in 100 days may actually mature in 93 days.

    Table 2. Date of Seeding Effect on Canola Maturity at Edmonton, AB and Brandon, MB
    Seeding Date Average Days to Maturity
    Brassica napus Brassica rapa
    Edmonton Brandon Edmonton Brandon
    May 1 120 105 98 90
    May 7 123 103 94 85
    May 15 123 100 90 70
    May 21 120 94 89 73
    May 30 113 90 89 70
    June 7 108 86 87 70
    June 12 101 81 85 69

     

    Table 3. Dates of Seeding and Swathing
    Seeding Date Range of Swathing Date
    Beaverlodge* Edmonton Brandon
    Brassica napus
    May 1 Aug. 18-Sept. 14 Aug. 27-Sept. 13 Aug. 12-16
    May 15 Sept. 1-19 Sept. 10-26 Aug. 21-26
    May 30 Sept. 13-Oct. 2** Sept. 12-26 Aug. 17-Sept. 7
    June 12 Oct. 5-25** Sept. 16-26 Sept. 10-17
    Brassica rapa
    May 1 Aug. 5-18 Aug. 9-14 July 29-Aug. 2
    May 15 Aug. 11-29 Aug. 12-17 Aug. 2-3
    May 30 Aug. 16-Sept. 13 Aug. 21-31 Aug. 4-17
    June 12 Aug. 31-Sept. 30 Aug. 29-Sept. 9 Aug. 20-25

     

    Rapa yields less sensitive to seeding date

    B. rapa (Polish canola) requires a shorter growing season and the relationship between early seeding and higher yield is not as strong as it is for B. napus. However, early seeding is still preferable for B. rapa so plants avoid midsummer heat stress and to ensure an early harvest. 


    Plant population effects

    Canola seeded early into cool soils will often have lower seedling survival. The following steps can improve survival rates for early seeded canola:

    • Seed as soon as frost risk for your area has declined. Canola can tolerate some frost damage, but there are limits to what the crop will withstand. If frost destroys the growing points of the canola seedlings, the plants will die and re-seeding may be necessary. Frost damage can also be greater in minimum or zero-tillage situations with heavy residue issues, since the soil is often cooler and less able to buffer cold air temperatures.
    • Temperatures in the seed zone should average at least 4-5 °C when measured over a 3-day period. Take temperatures twice a day, at 8 a.m. and 4 p.m., and take the 3-day average to determine general soil temperature. This is most important for very early seeding dates, when the odds that cool temperatures may continue following planting are highest. Canola can emerge in soils as cool as 2-3 °C, but seedling mortality will be higher and seedling emergence will be spread over more days.
    • Plan your seeding date based on the maturity of the variety. While seeding as soon as possible will reduce the risk of fall frost damage for any variety, early seeding may be more critical for varieties that need a longer season to mature.
    • Be prepared to initiate weed, disease and insect control early. Late applications of these inputs may erase any potential gains from earlier seeding. Threshold levels may need to be lowered if early-seeded canola is slow growing or if plant stands are reduced.
    • Consider using at least 10 kg/ha (10 lb./ac.) of phosphate in the seed row to help with pop up. At a rate of only 10 kg/ha, remember that granule or droplet spacing will be fairly wide down the row so seeds may not have equal access to the fertilizer. A higher rate will improve access for all seeds, but avoid excessive rates that will lead to increased seedling mortality.
    • Seed shallow and do not chase moisture.
    • Seed slower to ensure precise seed placement. 


    Effect on quality

    Early seeded canola tends to produce higher oil content and grade. [5] [8] Early seeding also leads to an earlier harvest, which reduces the risk for higher chlorophyll content in the seed and oil.

    Oil from early seeded canola tends to have lower saturated fat content. As a result, unsaturated fatty acid levels rise — but the shift is not consistent for all unsaturated fatty acids. Oleic acid increases with early seeding while linoleic and linolenic acids decrease. 

    Time of seeding does not significantly affect the erucic acid or glucosinolate content of canola. In years with hot, dry weather in late summer, early seeding can result in lower free fatty acids than later seeding.

    Oil and protein content often have an inverse relationship. Therefore, early seeded canola tends to have lower protein.


    References

    [1] Data from the Manitoba Agricultural Services Corporation show that from 1998-2008, canola seeded in the first two weeks of May had higher yields than canola seeded later. The only exception in Manitoba was the Interlake region, where canola seeded the second and third weeks of May had higher yields than canola seeded the first week of May. (See Table 1.)

    [2] AFSC Alberta crop insurance data for 2001-10 show that canola yields start to fall after the middle of May. The graph is a ratio of the average yield on the day to the average yield for the year.

    [3] Kondra, Z.P., 1977 “Effects of planted date on rapeseed.” Can. J. Plant Sci. 57: 607-609

    [4] Degenhardt, D.F., and Kondra, Z.P.,  1981 “The influence of seeding date and seeding rate on seed yield and yield components of five genotypes of Brassica napus.” Can J. Plant Sci., 61: 175-183

    [5] Kirkland, K.J., and Johnson, E.N., 2000 “Alternative seeding dates (fall and April) affect Brassica napus canola yield and Canadian Journal of Plant Science quality.”  Vol. 80 No. 4 pp. 713-719

    [6] Canola Council of Canada Canola Production Centre (CPC) trials in the late 1990s compared yields for fields seeded early, mid and late May. Seeding within the first 10 days of May produced the highest yields 70% of the time. Overall, the CPC trials found that canola seeded in late May yielded about 88% of canola seeded in early May.

    [7] Clayton et al, “Fall and spring seeding date effects on herbicide-tolerant canola (Brassica napus L.) cultivars” Published 2003 in the Canadian Journal of Plant Science.

    [8] Canola Production Centre trials found that oil content for canola seeded early May was 0.87 percentage points higher than canola seeded late May.

    [9] Peter F. Mills, “The effects of low temperature on the germination and emergence of canola.” Agriculture and Agri-Food Canada, Beaverlodge, Alta. Final report to the Alberta Agriculture Farming for the Future project 83-0036