| | Many of the vegetables grown in Alberta require a long growing season in order to mature and produce a crop. The growing season in Alberta varies with location, with the frost-free period being barely adequate or unsuitable in some areas for many crops. Many producers attempt to stretch out the season by seeding early, with the idea that seeding the crop early will get them ahead of the game. This is incorrect, as spring soil temperatures are typically well below optimum. Getting the seed in the ground early will not necessarily yield the anticipated benefits.
Why is germination important?
Good seed germination will help the crop get off to a good start and can significantly impact final yields and returns. Germination will affect plant stand and crop uniformity. Soil temperature, and more specifically the soil temperature in the seed zone, is critical to the level, rate and quality of seed germination. Slower germination increases the chance of infection by seed rot pathogens, which may result in uneven or poor plant stands and increased seed costs. Cool soil temperatures can also result in weak and slow growing seedlings.
Which temperature is best?
All crops have a minimum temperature for germination. Below this temperature, germination will not occur, as processes such as water uptake and enzymatic activity cannot take place. As soil temperatures approach the optimum for each crop, the rate and percentage of seed germination will increase. The following table presents soil temperature requirements for a variety of vegetable crops, with a corresponding rate of germination.
Crop | Minimum Temperature (°C)* | Optimum Temperature (°C)* | Days to Germination |
Celery | 4 | 21-23 | 10-14 |
Bean, Snap | 15 | 23-29 | 7 |
Beet | 4 | 23 | 7-14 |
Carrot | 4 | 23-26 | 12-15 |
Cole Crops (Cabbage, Cauliflower, Broccoli, etc) | 4 | 18-29 | 5-10 |
Cucumber | 15 | 21-29 | 7-10 |
Eggplant | 15 | 21-29 | 10 |
Lettuce | 0 | 18-21 | 7-10 |
Melon | 15 | 26-30 | 5-10 |
Onion (bulb) | 0 | 21-23 | 10-14 |
Onion (bunch) | 0 | 15-20 | 10-14 |
Pea | 4 | 18-21 | 7-14 |
Pepper | 15 | 23-29 | 10 |
Pumpkin | 15 | 21-23 | 7-10 |
Radish | 4 | 18-21 | 5-7 |
Spinach | 0 | 21 | 7-14 |
Sweet Corn | 10 | 21-29 | 7-10 |
Swiss Chard | 4 | 20-23 | 7-14 |
Tomato | 10 | 23-26 | 7-14 |
Turnip/Rutabaga | 15 | 18-21 | 7-14 |
* SOIL Temperature
Are there other options?
Vegetable growers should carefully consider the soil temperature requirements of the crops that they are growing when determining their seeding date. While growers can’t change the weather, they can implement some cultural practices that alter soil temperature or remove it as a factor. These practices may include the use of plastic mulches or row covers (microclimate modification) or using transplants. If growers must seed early, growers should consider seed treatments or other practices to prevent losses due to seed rot.
Other resources
Soil Temperature Conditions for Vegetable Seed Germination - Alabama Cooperative Extension System
Soil Temperature for Germination - Measurement, Other Crops
Seed Temperature Condition for Vegetable Seed Germination
Prepared by Robert Spencer Alberta Ag-Info Centre, Alberta Agriculture and Forestry |
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