The last week has seen the coolest weather for this winter spfar, -6; -7; -5 and soil temps have also dropped. Soil temps in my garden are hovering around 6 degrees. These low soil temperatures really limit seed germination. Soil temperature is probably the most important factor affecting seed germination, and seedling growth. Finding information about soil temperatures at which vegetable seeds will grow can sometimes be difficult and often not consistent. This is because there are different terms for classifying soil temps for germination purposes. There is the minimum temperature required for seed growth, an optimum temperature, and a realistic temperature. The minimum temperature is reasonably self explanatory. It is technically the minimum temperature at which germination is possible. On the other hand, the optimum soil temp is technically the perfect temperature for germination. However in between is the realistic temperature. This is somewhere between the minimum and the optimum temps at which germination and healthy growth can be achieved. This happy medium is suitable for beginning plant growth with the assumption that optimum temperatures will occur as the season progresses.
So for example, peas sown in soils with a temperature of 15 degrees take about nine days to germinate, while peas sown in soil with a temperature of 4 degrees about 36 days to germinate. By this time most of us will have given up. The other thing that can happen with this very long germination time is that seed often gets damaged and is far more likely to become diseased. However a soil temperature of around 10 degrees (the realistic soil temp) will see a much faster and better germination rate of about 70% and strong early growth.
To ensure success at this time of year it is much better to plant seedlings at this time of year while the soil temps are very cold. As the soil temperatures warm up by late winter to early spring much better seed germination rates will be achieved.
Don’t forget Wynlen House Urban Micro Farm is running its winter gardening workshop where you can learn all sorts of practical information about chemical free all season produce gardening particularly in a cold climate.