Soil temperature in Thunder Bay, Ontario
Soil temperature
21.4°C71°F
at 6cm — germination depth
Cooling over the next 11 days.
Seeding conditions are open — soil is 21.4°C at 6cm and holding above 12.5°C.
Most cool-season lawns in the northern US and Canada are bluegrass, tall fescue, or a mix of the two. We assume that, and use12.5°C as the seeding threshold.
I know what grass I have
The differences are small. Ryegrass is the quickest off the mark; bluegrass is the slowest and wants the warmest soil. Everything else sits between.
| Species | Soil temp | Days |
|---|---|---|
| Perennial ryegrass | 8°C | 5–10 |
| Red / chewings fescue | 8–10°C | 10–14 |
| Tall fescuelikely yours | 10–12°C | 10–14 |
| Browntop bentColonial bentgrass | 10–12°C | 14–21 |
| Smooth-stalked meadow grassKentucky bluegrasslikely yours | 12–13°C | 14–28 |
Soil temperature at 6cm in Thunder Bay, Ontario is currently 21.4°C, and falling about 19.4°C over the next 11 days. That depth matters because it is where grass seed sits and where roots start working, and it lags air temperature by days — which is why a warm afternoon here tells you very little on its own.
Lawns in this area are typically Kentucky bluegrass with tall fescue, the usual mix for cool-season lawns at this latitude. That blend needs the soil to hold above 12.5°C before seed germinates reliably. Seeding conditions are open — soil is 21.4°C at 6cm and holding above 12.5°C.
8 of the next 10 days are good mowing days. The other 2 are held back by wet grass or soft ground. The best weekend slot right now is Saturday 8am–9pm, on the basis that no rain since Monday, ground firm.
The next recommended window in Thunder Bay opens at 8pm on Tuesday 1 September, and holds while conditions stay put. Underfoot, the ground reads as firm after 4mm rain over the last week.
The next 10 days
Column height is how mowable the day is; the lighter band is the best stretch within it. The line is soil temperature at 6cm. It crosses the seeding threshold inside this forecast.
12.5°C — seeding
Soil at 6cm 21.4°C cooling to 0.0°C
Tuesday 1 September: Good. 8pm–9pm — cool — 25°C
Tuesday 1 September · 8pm–9pmConfident
8pm–9pm — cool — 25°C
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm4mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.98
- Marginal:Temperature
- Cool25°C
- Good:Wind
- Wind light15 km/h
- Sociable hours
- Your neighbours will remember it
Limiting factor:temperature
Wednesday 2 September: Good. 8am–9pm — no rain since Monday, ground firm
Wednesday 2 September · 8am–9pmConfident
8am–9pm — no rain since Monday, ground firm
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 1.00
- Good:Temperature
- Temperature15°C
- Good:Wind
- Wind light8 km/h
- Sociable hours
- A bit early or late, but finestarts at first light
Limiting factor:none
Thursday 3 September: Good. 8am–9pm — no rain since Monday, ground firm
Thursday 3 September · 8am–9pmConfident
8am–9pm — no rain since Monday, ground firm
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.92
- Good:Temperature
- Temperature13°C
- Good:Wind
- Wind light6 km/h
- Sociable hours
- A bit early or late, but finestarts at first light
Limiting factor:none
Friday 4 September: Good. 8am–9pm — no rain since Monday, ground firm
Friday 4 September · 8am–9pmConfident
8am–9pm — no rain since Monday, ground firm
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.80
- Good:Temperature
- Temperature14°C
- Good:Wind
- Wind light11 km/h
- Sociable hours
- A bit early or late, but finestarts at first light
Limiting factor:none
Saturday 5 September: Good. 8am–9pm — no rain since Monday, ground firm
Saturday 5 September · 8am–9pmReasonably confident
8am–9pm — no rain since Monday, ground firm
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.70
- Good:Temperature
- Temperature15°C
- Good:Wind
- Wind light8 km/h
- Sociable hours
- A bit early or late, but finestarts at first light
Limiting factor:none
Sunday 6 September: Good. 3pm–6pm — grass dry — rain earlier today
Sunday 6 September · 3pm–6pmReasonably confident
3pm–6pm — grass dry — rain earlier today
- Poor:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.85
- Good:Temperature
- Temperature15°C
- Good:Wind
- Wind light4 km/h
- Sociable hours
- Fine by the neighboursstarts once the dew has burnt off
Limiting factor:grass wetness
Monday 7 September: Good. 1pm–9pm — grass dry — dried off since a shower 3 hours ago
Monday 7 September · 1pm–9pmReasonably confident
1pm–9pm — grass dry — dried off since a shower 3 hours ago
- Marginal:Grass wetness
- Grass drydried off since a shower 3 hours ago
- Good:Ground firmness
- Ground firm10mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.95
- Good:Temperature
- Temperature17°C
- Good:Wind
- Wind light10 km/h
- Sociable hours
- Fine by the neighboursstarts once the dew has burnt off
Limiting factor:grass wetness
Tuesday 8 September: Good. 8am–9pm — barely growing — growth potential 0.17
Tuesday 8 September · 8am–9pmReasonably confident
8am–9pm — barely growing — growth potential 0.17
- Good:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm14mm rain over the last week
- Poor:Growth
- Barely growinggrowth potential 0.17
- Good:Temperature
- Temperature11°C
- Good:Wind
- Wind light16 km/h
- Sociable hours
- A bit early or late, but finestarts at first light
Limiting factor:growth
Wednesday 9 September: Not worth it. No — ground frozen.
Wednesday 9 SeptemberLow confidence this far out
No — ground frozen.
- Poor:Grass wetness
- Grass wetraining now
- Good:Ground firmness
- Ground soft in places14mm rain over the last week
- Good:Growth
- Growing steadilygrowth potential 0.35
- Good:Temperature
- Temperature13°C
- Good:Wind
- Wind light21 km/h
Limiting factor:grass wetness
Thursday 10 September: Not worth it. No — ground frozen.
Thursday 10 SeptemberLow confidence this far out
No — ground frozen.
- Marginal:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground soft in places35mm rain over the last week
- Marginal:Growth
- Growing slowlygrowth potential 0.31
- Good:Temperature
- Temperature10°C
- Good:Wind
- Wind light9 km/h
Limiting factor:grass wetness
Nearby
Your own postcode
These are town-centre figures. Yours will differ a little.