Portsmouth, Virginia
You are in the transition zone, where cool- and warm-season lawns both grow. These answers assume a cool-season lawn — ryegrass, fescue or bluegrass.
Best weekend slot
Sunday 10am–8pm
Verdict: Good
no rain since Saturday, ground firm
Next mow
Tomorrow 8am–9am
Verdict: Good
growing slowly — growth potential 0.23
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 29.3°C cooling to 0.0°C
Tuesday 1 September: Not worth it. No — heat stress, 30°C.
Tuesday 1 SeptemberConfident
No — heat stress, 30°C.
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Marginal:Growth
- Growing slowlygrowth potential 0.35
- Poor:Temperature
- Heat stress28°C
- Good:Wind
- Wind light6 km/h
Limiting factor:temperature
Wednesday 2 September: Good. 8am–9am — growing slowly — growth potential 0.23
Wednesday 2 September · 8am–9amConfident
8am–9am — growing slowly — growth potential 0.23
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Marginal:Growth
- Growing slowlygrowth potential 0.23
- Poor:Temperature
- Cool25°C
- Good:Wind
- Wind light9 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
Limiting factor:growth
Thursday 3 September: Good. 8am–9am — barely growing — growth potential 0.17
Thursday 3 September · 8am–9amConfident
8am–9am — barely growing — growth potential 0.17
- Good:Grass wetness
- Grass dryno rain since Monday
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Poor:Growth
- Barely growinggrowth potential 0.17
- Poor:Temperature
- Cool24°C
- Good:Wind
- Wind light6 km/h
- Sociable hours
- A bit early or late, but finestarts once the dew has burnt off
Limiting factor:growth
Friday 4 September: Good. 8am–10am — growing slowly — growth potential 0.21
Friday 4 September · 8am–10amConfident
8am–10am — growing slowly — growth potential 0.21
- Good:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm2mm rain over the last week
- Poor:Growth
- Growing slowlygrowth potential 0.21
- Poor:Temperature
- Cool24°C
- Good:Wind
- Wind light7 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
Limiting factor:growth
Saturday 5 September: Good. 8am–8pm — cool — 24°C
Saturday 5 September · 8am–8pmReasonably confident
8am–8pm — cool — 24°C
- Good:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm6mm rain over the last week
- Good:Growth
- Growing steadilygrowth potential 0.48
- Marginal:Temperature
- Cool24°C
- Good:Wind
- Wind light18 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
Limiting factor:temperature
Sunday 6 September: Good. 10am–8pm — no rain since Saturday, ground firm
Sunday 6 September · 10am–8pmReasonably confident
10am–8pm — no rain since Saturday, ground firm
- Good:Grass wetness
- Grass dryno rain since Saturday
- Good:Ground firmness
- Ground firm6mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.75
- Good:Temperature
- Temperature22°C
- Good:Wind
- Wind light17 km/h
- Sociable hours
- Fine by the neighboursstarts when it stops being antisocial
Limiting factor:none
Monday 7 September: Good. 10am–8pm — cool — 24°C
Monday 7 September · 10am–8pmReasonably confident
10am–8pm — cool — 24°C
- Good:Grass wetness
- Grass dryno rain since Saturday
- Good:Ground firmness
- Ground firm6mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.82
- Marginal:Temperature
- Temperature20°C
- Good:Wind
- Wind light4 km/h
- Sociable hours
- Fine by the neighboursstarts when it stops being antisocial
Limiting factor:temperature
Tuesday 8 September: Good. 8am–midday — no rain since Saturday, ground firm
Tuesday 8 September · 8am–middayReasonably confident
8am–midday — no rain since Saturday, ground firm
- Good:Grass wetness
- Grass dryno rain since Saturday
- Good:Ground firmness
- Ground firm4mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.72
- Poor:Temperature
- Temperature20°C
- Good:Wind
- Wind light7 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
Limiting factor:none
Wednesday 9 September: Not worth it. No — ground frozen.
Wednesday 9 SeptemberLow confidence this far out
No — ground frozen.
- Marginal:Grass wetness
- Grass dryno rain since Saturday
- Good:Ground firmness
- Ground firm4mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.79
- Good:Temperature
- Temperature22°C
- Good:Wind
- Wind light9 km/h
Limiting factor:none
Thursday 10 September: Not worth it. No — ground frozen.
Thursday 10 SeptemberLow confidence this far out
No — ground frozen.
- Good:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm5mm rain over the last week
- Good:Growth
- Growing steadilygrowth potential 0.36
- Poor:Temperature
- Cool24°C
- Good:Wind
- Wind light17 km/h
Limiting factor:growth
Soil temperature
87°F30.7°C
at 6cm — germination depth
Cooling over the next 11 days.
Too warm to seed — the soil is heat-stressed. Wait for it to cool.
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 |
What this means right now
Warning: Too warm to seed
Too warm to seed — the soil is heat-stressed. Wait for it to cool.
Warning: Heat stress
Tuesday 1 September gets hot enough to stress the sward. Mow early or late, and raise the height.
Worth watching: Worth knowing
You are in the transition zone, where cool- and warm-season lawns both grow. These answers assume a cool-season lawn — ryegrass, fescue or bluegrass.
Forecast from Open-Meteo, refreshed hourly. Soil temperature is modelled, not measured — how that works and where the thresholds come from.