Philadelphia, Pennsylvania
Mowing
When you can next cut it, and the best slot this weekend.
Best weekend slot
Sunday 10am–8pm
Verdict: Good
no rain since Friday, ground firm
Next mow
Tomorrow 6pm–8pm
Verdict: Good
heat stress — 27°C
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 23.2°C cooling to 0.0°C
Wednesday 2 September: Not worth it. No — grass wet, rain earlier today.
Wednesday 2 SeptemberConfident
No — grass wet, rain earlier today.
- Poor:Grass wetness
- Grass wetrain earlier today
- Good:Ground firmness
- Ground firm19mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.88
- Good:Temperature
- Temperature22°C
- Good:Wind
- Wind light7 km/h
Limiting factor:grass wetness
Thursday 3 September: Good. 6pm–8pm — heat stress — 27°C
Thursday 3 September · 6pm–8pmConfident
6pm–8pm — heat stress — 27°C
- Poor:Grass wetness
- Grass drydried off since a shower 4 hours ago
- Good:Ground firmness
- Ground firm28mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.81
- Marginal:Temperature
- Temperature22°C
- Good:Wind
- Wind light7 km/h
- Sociable hours
- A bit early or late, but finestarts once the dew has burnt off
Limiting factor:temperature
Friday 4 September: Good. 1pm–6pm — cool — 25°C
Friday 4 September · 1pm–6pmConfident
1pm–6pm — cool — 25°C
- Good:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm15mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.75
- Marginal:Temperature
- Temperature21°C
- Good:Wind
- Wind light6 km/h
- Sociable hours
- Fine by the neighboursstarts once the rain has passed
Limiting factor:temperature
Saturday 5 September: Good. 8am–8pm — rain earlier today, ground firm
Saturday 5 September · 8am–8pmConfident
8am–8pm — rain earlier today, ground firm
- Good:Grass wetness
- Grass dryrain earlier today
- Good:Ground firmness
- Ground firm17mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.82
- Marginal:Temperature
- Temperature19°C
- Good:Wind
- Wind light7 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
Limiting factor:none
Sunday 6 September: Good. 10am–8pm — no rain since Friday, ground firm
Sunday 6 September · 10am–8pmReasonably confident
10am–8pm — no rain since Friday, ground firm
- Good:Grass wetness
- Grass dryno rain since Friday
- Good:Ground firmness
- Ground firm17mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.95
- Good:Temperature
- Temperature18°C
- Good:Wind
- Wind light14 km/h
- Sociable hours
- Fine by the neighboursstarts when it stops being antisocial
Limiting factor:none
Monday 7 September: Good. 10am–8pm — no rain since Friday, ground firm
Monday 7 September · 10am–8pmReasonably confident
10am–8pm — no rain since Friday, ground firm
- Good:Grass wetness
- Grass dryno rain since Friday
- Good:Ground firmness
- Ground firm17mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.95
- Marginal:Temperature
- Temperature16°C
- Good:Wind
- Wind light8 km/h
- Sociable hours
- Fine by the neighboursstarts when it stops being antisocial
Limiting factor:none
Tuesday 8 September: Good. 8am–3pm — no rain since Friday, ground firm
Tuesday 8 September · 8am–3pmReasonably confident
8am–3pm — no rain since Friday, ground firm
- Good:Grass wetness
- Grass dryno rain since Friday
- Good:Ground firmness
- Ground firm17mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.84
- Marginal:Temperature
- Temperature19°C
- Good:Wind
- Wind light5 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
Limiting factor:none
Wednesday 9 September: Good. 8am–midday — no rain since Friday, ground firm
Wednesday 9 September · 8am–middayReasonably confident
8am–midday — no rain since Friday, ground firm
- Good:Grass wetness
- Grass dryno rain since Friday
- Good:Ground firmness
- Ground firm17mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.56
- Poor:Temperature
- Temperature22°C
- Good:Wind
- Wind light11 km/h
- Sociable hours
- A bit early or late, but finestarts when it stops being antisocial
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 firm9mm rain over the last week
- Good:Growth
- Growing steadilygrowth potential 0.35
- Poor:Temperature
- Heat stress26°C
- Good:Wind
- Wind light15 km/h
Limiting factor:growth
Friday 11 September: Not worth it. No — ground frozen.
Friday 11 SeptemberLow confidence this far out
No — ground frozen.
- Good:Grass wetness
- Grass dryno rain since Wednesday
- Good:Ground firmness
- Ground firm4mm rain over the last week
- Good:Growth
- Growing wellgrowth potential 0.91
- Good:Temperature
- Temperature18°C
- Good:Wind
- Wind light12 km/h
Limiting factor:none
Growth
How fast it is growing, and when it will need cutting again.
0.88Growing strongly
Growth potential, 0 to 1 — the turf-industry measure of how fast grass can grow at today's temperature and day length.
Putting on about 5.3mm a day. A lawn cut today would be ready for another in around 4 days.
Worked out from the PACE Turf growth potential model and day length —how and why.
What this means right now
Good: Seeding window open
Seeding conditions are open — soil is 23.3°C at 6cm and holding above 12.5°C.
Warning: Heat stress
Thursday 3 September gets hot enough to stress the sward. Mow early or late, and raise the height.
Seeding
Soil temperature at germination depth, and when the window opens.
Soil temperature
74°F23.3°C
at 6cm — germination depth
Cooling over the next 10 days.
Seeding conditions are open — soil is 23.3°C at 6cm and holding above 12.5°C.
Cross-checks against an independent estimate from air temperature (23.7°C), which agrees to within 0.5°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 |
Feeding
Why timing decides whether a feed does anything at all.
Coming in the app
Grass takes up nitrogen when it is growing. Feed a lawn that has stopped and most of it washes past the roots — which is why timing beats product choice.
Right now this lawn is growing well enough to use a feed.
The app will work out the actual feeding windows for your lawn — along with weed control, scarifying and moss treatment — and tell you when they open without you having to check.
Philadelphia, Pennsylvania in detail
Soil temperature at 6cm in Philadelphia, Pennsylvania is currently 23.3°C, and falling about 24.2°C over the next 10 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 23.3°C at 6cm and holding above 12.5°C.
7 of the next 10 days are good mowing days. The best weekend slot right now is Sunday 10am–8pm, on the basis that no rain since Friday, ground firm.
The next recommended window in Philadelphia opens at 6pm on Thursday 3 September, because that is when the dew has burnt off — earlier than that and you are cutting wet grass. Underfoot, the ground reads as firm after 19mm rain over the last week.
Forecast from Open-Meteo, refreshed hourly. Soil temperature is modelled, not measured — how that works and where the thresholds come from.