Cambridge, Massachusetts
Mowing
When you can next cut it, and the best slot this weekend.
Best weekend slot
Sunday 8am–6pm
Verdict: Prime time, >95% chance it holds
temperature — 11°C
Next mow
Tomorrow 8am–6pm
Verdict: Prime time, >95% chance it holds
temperature — 12°C
- Warning: Frost about. Monday 19 October has frosted hours. Stay off it until it lifts — walking on frosted grass bruises it, and mowing it ruptures the leaf. More
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.
Monday 19 October: nothing to cut. Nothing to cut — the grass is barely growing (growth potential 0.04). Conditions themselves are fine.
Monday 19 October, hour by hour 5am 6am 7am 8am 9am 10am 11am midday 1pm 2pm 3pm 4pm 5pm 6pm 7pm 8pm Chance — — — <5% >95% >95% >95% >95% >95% >95% >95% >95% >95% — — — Verdict nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing Rainchance 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% Rainmm — — — — — — — — — — — — — — — — Grass damp damp wet wet damp dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 2° 2° 1° 2° 5° 9° 11° 12° 13° 13° 13° 13° 12° 10° 9° 8° Windkm/h 2 6 4 4 2 2 4 7 11 12 12 12 10 7 8 7 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.04). Not enough to be worth cutting, which is why no hour is recommended today whatever the weather does.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 below it 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 actually hit.
Monday 19 OctoberConfident
Nothing to cut — the grass is barely growing (growth potential 0.04). Conditions themselves are fine.
>95% nothing to cut. Every forecast run agrees.
Nothing to cut. The odds below describe the weather only — growth decides whether a cut is wanted, and it is judged separately.
Limiting factor:growth
Tuesday 20 October: 10 hours worth using. 8am–6pm — temperature — 12°C
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% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% Rainmm — — — — — — — — — — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 6° 5° 5° 6° 9° 12° 14° 14° 15° 15° 15° 15° 14° 12° 11° 11° Windkm/h 10 9 7 9 14 17 22 23 24 24 25 23 19 14 10 10 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.12). 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.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 below it 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 actually hit.
Tuesday 20 October · 8am–6pmConfident
8am–6pm — temperature — 12°C
>95% prime time — the chance it holds right through, not the chance at any one hour. Every forecast run agrees.
Limiting factor:temperature
Wednesday 21 October: 10 hours worth using. 8am–6pm — temperature — 10°C
Wednesday 21 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% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 1% 0% 0% 0% 0% 1% 1% 0% 0% 0% 0% 4% 3% 0% 1% 4% Rainmm — — — — — — — — — — — — 0.2 — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 9° 9° 9° 9° 10° 9° 10° 10° 11° 12° 11° 11° 10° 10° 10° 10° Windkm/h 15 15 18 18 17 18 18 17 17 18 18 17 15 13 14 13 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.14). 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.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 below it 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 actually hit.
Wednesday 21 October · 8am–6pmConfident
8am–6pm — temperature — 10°C
>95% prime time — the chance it holds right through, not the chance at any one hour. Every forecast run agrees.
Limiting factor:temperature
Thursday 22 October: 10 hours worth using. 8am–6pm — temperature — 10°C
Thursday 22 October, hour by hour 5am 6am 7am 8am 9am 10am 11am midday 1pm 2pm 3pm 4pm 5pm 6pm 7pm 8pm Chance — — — 90% 90% 90% 90% 90% 90% 95% 95% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 5% 2% 1% 0% 2% 4% 3% 0% 0% 0% 0% 0% 0% 0% 0% 0% Rainmm 0.1 0.1 — — — 0.1 — — — — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 6° 6° 6° 6° 8° 10° 13° 15° 16° 17° 17° 17° 16° 13° 12° 12° Windkm/h 9 9 9 10 11 12 14 15 13 12 12 11 8 6 4 5 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.16). 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.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 below it 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 actually hit.
Thursday 22 October · 8am–6pmReasonably confident
8am–6pm — temperature — 10°C
90% prime time — the chance it holds right through, not the chance at any one hour. About 1 run in 10 found the grass too wet.
Limiting factor:temperature
Friday 23 October: 10 hours worth using. 8am–6pm — temperature — 10°C
Friday 23 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% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 3% 4% 0% 2% 1% 2% 1% 2% 2% 1% 1% 1% 1% 0% 2% 0% Rainmm 0.1 — — — — — — — 0.1 — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 8° 8° 7° 7° 8° 10° 11° 12° 13° 13° 13° 13° 12° 10° 10° 9° Windkm/h 11 11 8 9 12 15 16 15 15 15 15 15 15 13 12 11 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.15). 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.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 below it 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 actually hit.
Friday 23 October · 8am–6pmReasonably confident
8am–6pm — temperature — 10°C
95% prime time — the chance it holds right through, not the chance at any one hour. A handful of runs hit rain.
Limiting factor:temperature
Saturday 24 October: nothing to cut. Nothing to cut — the grass is barely growing (growth potential 0.08). Conditions themselves are fine.
Saturday 24 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% >95% >95% — — — Verdict nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing nothing to cut — the grass is barely growing Rainchance 0% 1% 0% 0% 0% 1% 1% 0% 0% 0% 0% 1% 0% 0% 0% 0% Rainmm — — — — — — — — — — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 4° 4° 4° 5° 6° 8° 10° 11° 12° 13° 13° 13° 13° 12° 10° 9° Windkm/h 6 6 6 6 5 4 3 2 2 2 3 3 4 5 6 7 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.08). Not enough to be worth cutting, which is why no hour is recommended today whatever the weather does.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 below it 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 actually hit.
Saturday 24 OctoberReasonably confident
Nothing to cut — the grass is barely growing (growth potential 0.08). Conditions themselves are fine.
>95% nothing to cut. Every forecast run agrees.
Nothing to cut. The odds below describe the weather only — growth decides whether a cut is wanted, and it is judged separately.
Limiting factor:growth
Sunday 25 October: 10 hours worth using. 8am–6pm — temperature — 11°C
Sunday 25 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% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% Rainmm — — — — — — — — — — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground frozen frozen frozen firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 5° 5° 5° 6° 8° 11° 13° 15° 17° 18° 17° 17° 16° 14° 12° 11° Windkm/h 8 8 7 8 8 10 11 12 13 13 13 13 12 12 13 13 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: barely growing (growth potential 0.14). 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.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 below it 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 actually hit.
Sunday 25 October · 8am–6pmReasonably confident
8am–6pm — temperature — 11°C
>95% prime time — the chance it holds right through, not the chance at any one hour. Every forecast run agrees.
Limiting factor:temperature
Monday 26 October: 10 hours worth using. 8am–6pm — temperature — 10°C
Monday 26 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% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 0% 0% 0% 1% 0% 0% 0% 1% 0% 1% 0% 0% 0% 0% 0% 0% Rainmm — — — — — — — — — — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 8° 8° 9° 9° 10° 12° 13° 15° 17° 18° 18° 18° 17° 16° 15° 14° Windkm/h 13 14 14 15 15 15 15 15 16 16 15 14 14 13 12 11 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — Growth: growing slowly (growth potential 0.21). 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.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 below it 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 actually hit.
Monday 26 October · 8am–6pmReasonably confident
8am–6pm — temperature — 10°C
>95% prime time — the chance it holds right through, not the chance at any one hour. Every forecast run agrees.
Limiting factor:temperature
Tuesday 27 October: 10 hours worth using. 8am–6pm — dry for over a week by then, ground firm
Tuesday 27 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% >95% >95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark dark Rainchance 0% 3% 1% 3% 1% 5% 3% 2% 1% 2% 0% 3% 3% 0% 0% 0% Rainmm — — — — — — — — — — — — — — — — Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm Temp 11° 10° 10° 11° 12° 15° 17° 18° 20° 20° 20° 20° 19° 18° 16° 15° Windkm/h 9 9 9 9 8 7 7 6 7 8 8 8 9 9 9 9 Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — — 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.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 below it 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 actually hit.
Tuesday 27 October · 8am–6pmLow confidence this far out
8am–6pm — dry for over a week by then, ground firm
90% prime time — the chance it holds right through, not the chance at any one hour. About 1 run in 10 hit rain.
Limiting factor:none
Wednesday 28 October: 10 hours worth using. 8am–6pm — dry for over a week by then, ground firm
Wednesday 28 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% >95% 95% — — — Verdict dark dark dark Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time Prime time dark dark Already gone Rainchance 4% 2% 1% 1% 3% 5% 0% 3% 3% 5% 1% 3% 6% 1% 0% · Rainmm — — — — — — — — — — — — 0.1 — — · Grass dry dry dry dry dry dry dry dry dry dry dry dry dry dry dry · Ground firm firm firm firm firm firm firm firm firm firm firm firm firm firm firm · Temp 13° 13° 14° 14° 15° 17° 18° 19° 20° 21° 20° 17° 15° 14° 12° · Windkm/h 12 12 12 12 12 13 14 15 16 17 17 17 19 19 19 · Daylight — — — ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ — — · Growth: growing steadily (growth potential 0.44). 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.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 below it 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 actually hit.
Wednesday 28 October · 8am–6pmLow confidence this far out
8am–6pm — dry for over a week by then, ground firm
85% prime time — the chance it holds right through, not the chance at any one hour. About 1 run in 6 hit rain.
Limiting factor:none
good to go touch and go dark, frost or snow already goneFainter means fewer forecast runs agree.
Growth
How fast it is growing, and when it will need cutting again.
4%Barely growing
Of the fastest this grass could grow. The turf-industry measure, from today's temperature and day length.
The lawn is barely growing, so it does not need cutting. Leave it — taking leaf off a sward that cannot replace it costs more than it gives.
Held back by both temperature and short days — 10.9 hours of daylight at 7°C.
- Over the next 10 days
- about 7mm of leaf
- Next cut due
- not within the next ten days
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 Cambridge, Massachusetts
41°F5.2°C
at 6cm — germination depth
Too cold to seed — 5.2°C at 6cm and not warming.
Cooling over the next 10 days.
Cross-checks against an independent estimate from air temperature (8.6°C), which agrees to within 0.4°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 not growing fast enough to make much use of 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.
Cambridge, Massachusetts in detail
Soil temperature in Cambridge, Massachusetts is currently 5.2°C at 6cm, and falling about 4.6°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. Too cold to seed — 5.2°C at 6cm and not warming.
8 of the next 10 days are good mowing days. The best weekend slot right now is Sunday 8am–6pm, on the basis that temperature — 11°C.
The next recommended window in Cambridge opens at 8am on Tuesday 20 October, because that is first light. Underfoot, the ground reads as firm after 21mm rain over the last week, medium (loam) soil.
There is frost in the forecast for Cambridge, Massachusetts: Monday 19 October has hours cold enough to freeze the leaf. Stay off the grass until it lifts — mowing frosted turf ruptures the cells and the damage shows for weeks.
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.