Planting Date
Planting date is one of the most important management tools available to maximize yield potential. Late seeded crops do not have adequate time to “catch up” with early seeded plants in most of Ontario, see figure 1.
Figure 1. Vegetative plant growth differences based on planting date. Plot on left was planted in May. Plot on right was planted in June.
Soybean planting should begin based on:
- Calendar date. If springtime conditions are favourable, planting in late April or early May can result in a yield advantage compared to planting in the middle of May or later.
- Seedbed conditions. It is crucial to have a good seedbed. A good seedbed should have soil which easily crumbles, with adequate soil moisture.
- Weather forecast for 48 hours after planting. If significant rainfall is forecasted, wait until conditions improve before planting to avoid crusting and imbibitional chilling injury. A cold rain immediately after seeding will impact emergence.
Yield response to planting date will vary depending on the growing season and the maturity group (MG) of the variety. On average, the highest yields are obtained from relatively early planting. The exact date that is considered “early” depends on the growing region in Ontario. In southern Ontario, April 15th would be considered early for soybeans. In northern Ontario, May 20th may be considered early. One of the main concerns with planting early is that a hard spring frost can kill soybeans, since the growing point of the emerged seedling is above the soil surface. However, soybean plants can withstand temperatures as low as -2.8°C for a short period of time, while corn experiences tissue damage at -2°C.
Late planting is likely to incur significant yield reductions, see Table 1, Effect of Planting Date on Yield. When planting early, select a variety that is adapted or longer season (0.5 MG) for a given area for maximum yields.
Table 1. Effect of Planting Date on Yield
| Planting Date | Yield | Percent of Full Yield (%) |
| April 15 – May 5 | 4.29 t/ha (63.8 bu/acre) | 100 |
| May 6 – May 20 | 4.26 t/ha (63.3 bu/acre) | 99 |
| May 21 – June 5 | 3.93 t/ha (58.5 bu/acre) | 92 |
| The data in this table represents the average of 22 trials across Ontario from 2010-2012. | ||
There is a concern that planting later-maturing varieties (higher MG) will delay winter wheat seeding after soybean harvest. A balance must be stuck between choosing a high yielding variety which usually means a higher MG, but one that will also mature in time for winter wheat planting. A long-season variety yielded 0.28 to/ha (4.1 bu/ac) more compared to an adapted variety, in a 22 site-year Ontario study, see Table 2, Yield of an Adapted Variety Compared to a Long-Season Variety. One of the advantages of planting early is that the crop will also be ready for harvest earlier. If planted before the middle of May a long-season variety (0.5 – 0.8 MG longer than adapted) will only result in a 1–5 day delay in harvest, compared to seeding an adapted variety in late May.
Table 2. Yield of an Adapted Variety Compared to a Long-Season Variety
| Average of 22 trials across Ontario from 2010-2012. | ||
| Planting Date | Variety | Yield |
| Mid-May (May 6 – May 20) | Adapted for the area based on Relative Maturity Map | 4.17 t/ha (62.1 bu/acre) |
| Early Planting (April 15 – May 5) | Adapted for the area based on Relative Maturity Map | 4.23 t/ha (62.9 bu/acre) |
| Early Planting (April 15 – May 5) | Long-Season Variety (0.5 – 0.8 MG) for the area based on Relative Maturity Map | 4.45 t/ha (66.2 bu/acre) |
Field experience has shown that if August conditions are dry, early planting of a short-season (low MG) variety will reduce yields. The short-season variety will mature too early in the fall and not be able to take advantage of late-season rains.
Delayed Planting
When planting is delayed, fewer days are required for the plant to reach maturity. Due to the photoperiod effect soybeans will adjust (within reason) to the growing season. For example, a 3-week delay in planting results in about a 7-day delay of maturity. The photoperiod effect is more evident in higher MG varieties compared to short season varieties. Delayed planting reduces the vegetative growth period which results in shorter plants with significantly fewer nodes. Late planting also shortens the flowering period and shortens the duration of the pod-filling period. Late planting (June) reduced yield by up to 20% depending on the variety and the location in one Ontario study, see Table 3, Planting Date and Maturity Group Impact on Relative Yield. This study demonstrates that planting an extremely long season (very high MG) variety can reduce yield. This study also showed that if planting is delayed to mid June, varieties should not be switched to shorter season varieties (lower MG). The adapted variety yielded the best when planting was delayed to mid June.
Table 3. Planting Date and Maturity Group Impact on Relative Yield.
| Planting Date** | |||
| Maturity Group (MG) | Late April | Mid May | Mid June |
| Elora | % of maximum yield | ||
| 0.1 | 82 | 84 | 74 |
| 0.3 | 86 | 88 | 77 |
| 1.0* | 98 | 100 | 82 |
| 1.7 | 98 | 93 | 77 |
| 2.5 | 100 | 93 | 73 |
| Mean | 93 | 92 | 76 |
| Winchester | |||
| 0.1 | 76 | 80 | 73 |
| 0.3 | 85 | 83 | 75 |
| 1.0 | 90 | 90 | 82 |
| 1.7 | 100 | 97 | 80 |
| 2.5 | 93 | 89 | 75 |
| Mean | 89 | 88 | 77 |
| Ridgetown | |||
| 1.1 | 92 | 84 | 76 |
| 1.8 | 92 | 87 | 75 |
| 2.5 | 100 | 93 | 83 |
| 3.2 | 93 | 89 | 73 |
| 3.6 | 93 | 94 | 76 |
| Mean | 94 | 89 | 77 |
| Notes: Percent yields are relative to the highest yielding planting date and MG combination at each site. 9 site years 2021-2023. *Bold = MG considered full-season or “adapted” for that growing area ** actual planting date for late April and mid May were delayed in 2023 by 10-14 days in 2023 at all locations. Source: Seth Ritsma, David Hooker | |||
If planting must be delayed past July 1st:
- On heavy textured soils, select a full season (adapted) variety. Planting a short-day variety, late in the season results in extremely short plants with few pods. An early frost may cause darkened hilums which “bleed” into the soybean. If “bleeding” is a concern, select a light-colored hilum variety.
- On medium or light textured soils, choose a variety that is 0.5-1.0 MG less than adapted will aid in reaching maturity before a killing frost.
- When late planting, wide rows will lead to reduced yield potential. Instead, plant in narrow rows and increase the seeding rate by at least 10%. Also, vegetative growth of late plantings can be improved by selecting taller varieties. This will increase the height of the low-set pods as well as the number of pods per acre.
Soil Temperature
If the soil is fit for planting (adequately dry) and there is no cold rain forecast within 48 hours, soybeans can be seeded into relatively cold soils. The first 48 hours after seeding are particularly important. If the seed imbibes very cold water at that stage imbibitional chilling injury may occur. After the first 48 hours the risk of imbibitional chilling injury is greatly reduced. A cold rain soon after planting is usually the trigger for imbibitional chilling injury. Although plant stands are often reduced with early planting compared to waiting for ideal temperatures the yield benefits of early planting outweigh the risks of early planting. Unlike corn, soybeans do not need a perfect plant stand. In recent years some growers have decided to plant soybeans before corn because corn needs a more perfect plant stand. From an overall yield perspective, both crops benefit from planting early. It is not necessary to wait for soil temperature to be above 10 degrees Celsius to plant soybeans. A fungicide seed treatment is recommended when planting early. Generally speaking, if soil temperature and moisture conditions are suitable for planting corn, they are also suitable for soybeans.