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.
Mowing
When you can next cut it, and the best slot this weekend.
Current conditions · 11am, this hour
Prime time>95% chance
- Grass
- dry
- Ground
- firm
- Rain
- 0% chance
- Temp
- 19°
- Wind
- 23 km/h
Forecast for this hour, not a measurement.
Best weekend slot
Saturday 8am–7pm
Verdict: Prime time, >95% chance at its best hour
dry since Saturday by then, ground firm
Next mow
Now until 7pm
Verdict: Prime time, >95% chance at its best hour
no rain since Saturday, ground firm
The next 10 days
Each row is a day, morning on the left. The more solid a block, the more of the forecast runs agree you can mow. Open a day for the hour-by-hour forecast behind it.
Tuesday 20 October: 8 hours worth using. Now until 7pm — no rain since Saturday, ground firm
Tuesday 20 October, hour by hour 5am 6am 7am 8am 9am 10am 11am midday 1pm 2pm 3pm 4pm 5pm 6pm 7pm 8pm Chance — — — — — — >95% >95% >95% >95% >95% >95% >95% >95% — — Verdict Already gone Already gone Already gone Already gone Already gone Already gone Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark Rainchance · · · · · · 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% Rainmm · · · · · · — — — — — — — — — — Grass · · · · · · dry dry dry dry dry dry dry dry dry dry Ground · · · · · · firm firm firm firm firm firm firm firm firm firm Temp · · · · · · 19° 20° 20° 20° 20° 20° 19° 18° 17° 16° Windkm/h · · · · · · 23 27 26 27 27 27 24 19 15 13 Daylight · · · · · · ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — Growth: growing well (growth potential 0.50). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Tuesday 20 October · now until 7pmConfident
Now until 7pm — no rain since Saturday, ground firm
>95% prime time at its best hour, >95% that all 8 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Wednesday 21 October: 11 hours worth using. 8am–7pm — dry since Saturday by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing steadily (growth potential 0.47). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Wednesday 21 October · 8am–7pmConfident
8am–7pm — dry since Saturday by then, ground firm
>95% prime time at its best hour, >95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Thursday 22 October: 11 hours worth using. 8am–7pm — dry since Saturday by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing steadily (growth potential 0.41). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Thursday 22 October · 8am–7pmConfident
8am–7pm — dry since Saturday by then, ground firm
>95% prime time at its best hour, >95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Friday 23 October: 11 hours worth using. 8am–7pm — dry since Saturday by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing well (growth potential 0.54). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Friday 23 October · 8am–7pmConfident
8am–7pm — dry since Saturday by then, ground firm
>95% prime time at its best hour, 95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Saturday 24 October: 11 hours worth using. 8am–7pm — dry since Saturday by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing well (growth potential 0.53). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Saturday 24 October · 8am–7pmReasonably confident
8am–7pm — dry since Saturday by then, ground firm
>95% prime time at its best hour, >95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Sunday 25 October: 11 hours worth using. 8am–7pm — dry for over a week by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing well (growth potential 0.58). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Sunday 25 October · 8am–7pmReasonably confident
8am–7pm — dry for over a week by then, ground firm
>95% prime time at its best hour, >95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Monday 26 October: 11 hours worth using. 8am–7pm — dry for over a week by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing well (growth potential 0.63). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Monday 26 October · 8am–7pmReasonably confident
8am–7pm — dry for over a week by then, ground firm
>95% prime time at its best hour, >95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Tuesday 27 October: 11 hours worth using. 8am–7pm — dry for over a week by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing well (growth potential 0.68). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Tuesday 27 October · 8am–7pmReasonably confident
8am–7pm — dry for over a week by then, ground firm
>95% prime time at its best hour, >95% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Wednesday 28 October: 11 hours worth using. 8am–7pm — dry for over a week by then, ground firm
Loading the hour-by-hour forecast…
Growth: growing steadily (growth potential 0.38). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Wednesday 28 October · 8am–7pmLow confidence this far out
8am–7pm — dry for over a week by then, ground firm
>95% prime time at its best hour, 85% that all 11 hours stay mowable. Every forecast run agrees.
Limiting factor:none
Thursday 29 October: 11 hours worth using. 8am–7pm — ground firm — 0mm rain over the last week, medium (loam) soil
Loading the hour-by-hour forecast…
Growth: growing slowly (growth potential 0.25). Enough to be worth cutting. Growth decides whether a cut is wanted, not how well it will go, so it is not one of the rows above and does not move the chances.
Thursday 29 October · 8am–7pmLow confidence this far out
8am–7pm — ground firm — 0mm rain over the last week, medium (loam) soil
95% prime time at its best hour, 85% that all 11 hours stay mowable. A handful of runs hit rain.
Limiting factor:ground firmness
good to go touch and go dark, frost or snow already goneFainter means fewer forecast runs agree.
Chance is the share of 82 forecast runs — the same weather models re-run from slightly different starting conditions — in which you could have mowed that hour. The rows under it in each day's table are what those runs expect on average, which is why an hour can look reasonable line by line and still fall short: the chance only counts runs where everything came together at once. Hover any cell for what the runs that ruled it out hit.
Growth
How fast it is growing, and when it will need cutting again.
50%Growing steadily
Of the fastest this grass could grow. The turf-industry measure, from today's temperature and day length.
Roughly 2mm a day. A lawn cut today would be ready for another in about a week.
- Over the next 10 days
- about 17mm of leaf
- Next cut due
- in about a week
This only knows temperature and day length. Feeding, watering, shade and cutting height all move it, so treat it as a rough guide.
Worked out from the PACE Turf growth potential model and day length —how and why.
Seeding
Soil temperature at germination depth, and when the window opens.
Soil temperature in Portsmouth, Virginia
62°F16.6°C
at 6cm — germination depth
Seeding conditions are open — soil is 16.6°C at 6cm and holding above 12.5°C.
Cooling over the next 10 days.
Cross-checks against an independent estimate from air temperature (15.5°C), which agrees to within 1.1°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 use 12.5°C as the seeding threshold.
Thresholds for every species
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 needed | Days to sprout |
|---|---|---|
| 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.
Portsmouth, Virginia in detail
Soil temperature in Portsmouth, Virginia is currently 16.6°C at 6cm, and falling about 4.7°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 16.6°C at 6cm and holding above 12.5°C.
10 of the next 10 days are good mowing days. The best weekend slot right now is Saturday 8am–7pm, on the basis that dry since Saturday by then, ground firm.
The next recommended window in Portsmouth opens at 11am on Tuesday 20 October, and holds while conditions stay put. Underfoot, the ground reads as firm after 23mm rain over the last week, medium (loam) soil.
Save this lawn and we will email you when the windows open.
We already send you the forecast email? Use the same address.
Chances counted across 82 forecast runs from NCEP GEFS, 25km and ECMWF IFS ensemble, 25km. Forecast from Open-Meteo, refreshed through the day. Soil temperature is modelled, not measured — how that works and where the thresholds come from.