How early should you plant your crop? In Manitoba, the general rule of thumb appears to be the earlier the better — but not too early, especially with plants susceptible to spring frosts or requiring warm soil for germination.
Cautionary note: When crops are sown too early, they can be exposed to an increased risk of spring frost. These figures do not reflect early frost losses. These figures only include the average yields of crops which have completed establishment in the spring (i.e. the last crop), and do not include the yield losses associated with the initial first crop when reseeding occurs. Proper interpretation of the figures requires the interpreter to also consider the likelihood of a particular crop in a particular region having a killing spring frost on a certain date.
2005 - 2013: Seeding Date vs. Average Yield Response
Figure 1 shows the average relative yield reported to MASC during each sowing week for the selected crops grown in Manitoba for the period of 2005 - 2013. The vertical axis represents the percentage of average yield, and the horizontal axis represents the week each crop is sown.
1989 - 2008: Seeding Date vs. Average Yield Response
Figure 2 illustrates the average relative yield (%) reported to MASC during each sowing week for the selected crops grown in Manitoba over a 20-year period. The vertical axis represents the percentage of average yield, and the horizontal axis represents the week each crop is sown.
The vertical line represents the 4th week of May - By the 4th week of May sunflower, canola, soybean and edible beans haven’t lost a lot of yield potential, while spring seeded cereals, peas and corn yields have dropped to 85% of normal yield potential.
1981 - 2001: Seeding Date vs. Average Yield Response
Figure 3 illustrates the average relative reported yield for each week of the sowing season for Red Spring wheat, barley, oats, peas, flax and Argentine Canola over the 21 period 1981 to 2001, inclusive.
Generally, cereals had the highest yields the earlier the planting and they had a more rapid decline in yield than did broadleaf crops for every week planting was delayed. The main factor limiting yield on later sown cereals is likely the increasing prevalence of leaf and other diseases with delayed planting.
For the broadleaf crops, sowing too early resulted in reduced yields relative to later plantings, but early plantings were still superior to later plantings. The main factor increasing yields of earlier seeded broadleaf crops is likely the earlier bloom set of earlier plantings which results in greater avoidance of summer heat waves.
Figure 4 shows the average percentage of crop acres sown at weekly intervals in a cumulative fashion for each of Red Spring wheat, barley, oats, peas, flax and Argentine canola over the 21-year period from 1981 to 2001, inclusive.
On average at least 70 per cent of the Manitoba acreage of these crops is sown in one month — May. At least half the acres of RS wheat, barley and peas are sown by the second week of May or in the case of oats, flax and Argentine canola by the third week of May. Sowing of these crops is largely completed (90 per cent sown) during the fourth week of May for RS wheat and peas, and during the first week of June for barley, oats, flax and Argentine canola. Also note that by the third week of June over 95 per cent of the acreage of all these crops has been sown.