Guelph, Ontario

Guelph, Ontario43.5459, -80.2560

Mowing

When you can next cut it, and the best slot this weekend.

Best weekend slot

Sunday 9am–7pm

Verdict: Prime time, >95% chance it holds

temperature — 11°C

Next mow

Today 9am–7pm

Verdict: Prime time, >95% chance it holds

temperature — 11°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.

  1. Monday 19 October: 10 hours worth using. 9am–7pm — temperature — 11°C
    Monday 19 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———<5%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    Verdictdarkdarkdarkfrost on the grass — the blades will shatter rather than cutPrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timedarkdark
    Rainchance0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp4°3°3°2°5°11°14°16°17°18°19°19°18°16°13°11°
    Windkm/h999891314131213141311899
    Daylight———✓✓✓✓✓✓✓✓✓✓✓——

    Growth: barely growing (growth potential 0.13). 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 19 October · 9am–7pmConfident

    9am–7pm — 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

  2. Tuesday 20 October: 11 hours worth using. 8am–7pm — temperature — 12°C
    Tuesday 20 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    VerdictdarkdarkdarkPrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timedarkdark
    Rainchance0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp5°6°6°6°8°10°12°13°14°15°16°16°15°13°9°7°
    Windkm/h9111111121615151412121312888
    Daylight———✓✓✓✓✓✓✓✓✓✓✓——

    Growth: barely growing (growth potential 0.11). 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–7pmConfident

    8am–7pm — 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

  3. Wednesday 21 October: nothing to cut. Nothing to cut — the grass is barely growing (growth potential 0.08). Conditions themselves are fine.
    Wednesday 21 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    Verdictnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growing
    Rainchance0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp5°4°4°4°6°9°11°13°14°15°15°15°15°12°9°8°
    Windkm/h778871011111010963555
    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.

    Wednesday 21 OctoberConfident

    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

  4. Thursday 22 October: 11 hours worth using. 8am–7pm — temperature — 12°C
    Thursday 22 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    VerdictdarkdarkdarkPrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timedarkdark
    Rainchance0%0%0%0%0%0%0%0%1%0%0%2%1%0%0%0%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp6°6°6°6°8°12°14°16°17°18°18°18°18°15°12°10°
    Windkm/h9101010989101112131312111211
    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.

    Thursday 22 October · 8am–7pmConfident

    8am–7pm — 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

  5. Friday 23 October: nothing to cut. Nothing to cut — the grass is barely growing (growth potential 0.08). Conditions themselves are fine.
    Friday 23 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———<5%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    Verdictnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growing
    Rainchance0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfrozenfrozenfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp6°6°5°5°6°8°10°11°12°12°12°12°11°9°6°5°
    Windkm/h14131313152021212021212018161313
    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.

    Friday 23 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

  6. Saturday 24 October: nothing to cut. Nothing to cut — the grass is barely growing (growth potential 0.06). Conditions themselves are fine.
    Saturday 24 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———<5%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    Verdictnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growing
    Rainchance0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%0%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfrozenfrozenfrozenfrozenfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp4°3°3°4°6°9°11°13°14°15°16°16°15°13°10°8°
    Windkm/h111110991012121313131414131211
    Daylight———✓✓✓✓✓✓✓✓✓✓✓——

    Growth: barely growing (growth potential 0.06). 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 0.06). 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

  7. Sunday 25 October: 10 hours worth using. 9am–7pm — temperature — 11°C
    Sunday 25 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———<5%>95%>95%>95%>95%>95%>95%>95%>95%>95%>95%——
    Verdictdarkdarkdarkground frozenPrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timedarkdark
    Rainchance0%0%0%0%1%0%0%0%1%1%3%0%1%0%0%3%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfrozenfrozenfrozenfrozenfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp7°6°6°7°9°11°13°15°16°17°17°15°14°14°14°14°
    Windkm/h12121212162024262728272625252525
    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 · 9am–7pmReasonably confident

    9am–7pm — 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

  8. Monday 26 October: 11 hours worth using. 8am–7pm — temperature — 12°C
    Monday 26 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———>95%>95%>95%>95%>95%>95%95%95%>95%>95%>95%——
    VerdictdarkdarkdarkPrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timedarkdark
    Rainchance0%0%0%3%1%2%2%4%1%7%5%4%4%1%5%4%
    Rainmm——————————————0.1—
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp11°10°9°9°10°12°14°15°16°16°16°16°15°13°10°8°
    Windkm/h13121314182327282827252118151310
    Daylight———✓✓✓✓✓✓✓✓✓✓✓——

    Growth: growing slowly (growth potential 0.33). 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–7pmReasonably confident

    8am–7pm — temperature — 12°C

    85% good to go — the chance it holds right through, not the chance at any one hour. About 1 run in 6 hit rain.

    Limiting factor:temperature

  9. Tuesday 27 October: 11 hours worth using. 8am–7pm — temperature — 11°C
    Tuesday 27 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———90%90%95%>95%95%>95%>95%95%95%95%95%——
    VerdictdarkdarkdarkPrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timePrime timedarkdark
    Rainchance3%0%1%1%1%3%1%5%3%0%5%1%3%0%3%1%
    Rainmm————————————————
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydrydry
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm
    Temp7°7°7°8°11°14°16°16°14°12°12°12°12°11°9°8°
    Windkm/h10111214172328282523232322181617
    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 27 October · 8am–7pmLow confidence this far out

    8am–7pm — temperature — 11°C

    80% good to go — the chance it holds right through, not the chance at any one hour. About 1 run in 4 found the grass too wet.

    Limiting factor:temperature

  10. Wednesday 28 October: nothing to cut. Nothing to cut — the grass is barely growing (growth potential 0.02). Conditions themselves are fine.
    Wednesday 28 October, hour by hour
    5am6am7am8am9am10am11ammidday1pm2pm3pm4pm5pm6pm7pm8pm
    Chance———<5%<5%<5%95%>95%>95%>95%>95%>95%>95%<5%——
    Verdictnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingnothing to cut — the grass is barely growingAlready gone
    Rainchance1%0%4%1%1%1%4%3%0%2%0%4%4%3%4%·
    Rainmm———————————————·
    Grassdrydrydrydrydrydrydrydrydrydrydrydrydrydrydry·
    Groundfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirmfirm·
    Temp4°4°3°3°3°4°4°5°6°6°6°6°5°4°2°·
    Windkm/h131313141620222324242424221915·
    Daylight———✓✓✓✓✓✓✓✓✓✓✓—·

    Growth: barely growing (growth potential 0.02). 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.

    Wednesday 28 OctoberLow confidence this far out

    Nothing to cut — the grass is barely growing (growth potential 0.02). 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

good to go touch and go dark, frost or snow already goneFainter means fewer forecast runs agree.

How you feel about mowing

Sensible middle ground.

Petrol or battery. The baseline.

Growth

How fast it is growing, and when it will need cutting again.

13%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 10°C.

Over the next 10 days
about 4mm 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 Guelph, Ontario

6.6°C44°F

at 6cm — germination depth

Too cold to seed — 6.6°C at 6cm and not warming.

Cooling over the next 10 days.

Cross-checks against an independent estimate from air temperature (9.1°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 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.

Soil temperature at 6cm for reliable germination. Sources onthe method page.
SpeciesSoil neededDays to sprout
Perennial ryegrass8°C5–10
Red / chewings fescue8–10°C10–14
Tall fescuelikely yours10–12°C10–14
Browntop bentColonial bentgrass10–12°C14–21
Smooth-stalked meadow grassKentucky bluegrasslikely yours12–13°C14–28

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.

Why timing beats product choice

Guelph, Ontario in detail

Soil temperature in Guelph, Ontario is currently 6.6°C at 6cm, and falling about 6.0°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 — 6.6°C at 6cm and not warming.

5 of the next 10 days look workable. The best weekend slot right now is Sunday 9am–7pm, on the basis that temperature — 11°C.

The next recommended window in Guelph opens at 9am on Monday 19 October, because anything earlier is the hour your neighbours will remember. Underfoot, the ground reads as firm after 3mm rain over the last week, medium (loam) soil.

There is frost in the forecast for Guelph, Ontario: 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.

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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.