How long does grass seed take to grow?
Grass seed germinates in 5 to 10 days at 8°C and above, and up to four weeks for slow species. Soil temperature sets the clock, and here is how to read yours.
Published 24 September 2026 ·Last reviewed 24 September 2026
Grass seed takes 5 to 10 days to germinate when the soil holds at 8°C or warmer, and up to four weeks for slow species like smooth-stalked meadow grass. The “about a fortnight” answer people give is an average across species and conditions, and averages are what send people out to sow too early. The clock is set by soil temperature at seed depth, and everything else is secondary.
Germination times by species
The range depends mostly on what is in the bag. A UK ryegrass and fescue mix is fast. A mix heavy on meadow grass or bent is not.
| Species | Reliable germination | Typical days to germinate |
|---|---|---|
| Perennial ryegrass | ~8°C / 46°F | 5 to 10 |
| Red and chewings fescue | ~8-10°C / 46-50°F | 10 to 14 |
| Tall fescue | ~10-12°C / 50-54°F | 10 to 14 |
| Browntop bent (colonial bentgrass) | ~10-12°C / 50-54°F | 14 to 21 |
| Smooth-stalked meadow grass (Kentucky bluegrass) | ~12-13°C / 54-55°F | 14 to 28 |
Thresholds and ranges as compiled in our germination temperature guide, from Penn State Extension, Oregon State University’s seed laboratory and University of Minnesota Extension. Bag labels rarely tell you this, so check the species list on the box. If ryegrass leads the list, you are in the 5 to 10 day row.
Why soil temperature is the factor that matters
Seed germinates on accumulated warmth in the seed zone, which is the top couple of centimetres of soil. Daytime air temperature is a poor guide. A 20°C afternoon in March lifts the surface briefly while the seed zone sits at 7°C, and the seed does nothing.
Two patterns people get wrong:
- One warm day is not a sowing signal. What matters is the threshold being held. Mowdar’s method page defines a sowing window as five consecutive days at or above the species threshold, because germination responds to sustained warmth rather than a spike.
- Spring and autumn are not symmetric. In spring the soil is warming, so crossing 8°C usually means it keeps climbing. In autumn the soil is cooling, so crossing 8°C on the way down means conditions get worse every week after you sow.
We measure this per location on the soil temperature page: modelled soil temperature at 6cm, with the trajectory for the days ahead. For seed that is the direction indicator; the seed zone itself runs a little warmer by day and cooler by night.
What else slows germination down
Temperature sets the range. These decide where in it you land.
- Dry surface soil. Seed needs consistent moisture from sowing to emergence. University of Minnesota Extension describes keeping the seedbed moist without waterlogged, watering lightly and often in dry spells rather than heavily and rarely.
- Poor seed-to-soil contact. Seed sitting on thatch or loose debris germinates patchily. Rake the surface so seed falls to soil.
- A cold snap after sowing. Germination does not reverse, it pauses. In spring a pause costs days. In autumn, when the soil is cooling, a pause can run into winter.
Spring sowing versus autumn sowing
Autumn sowing has one structural advantage: the soil is warm from summer, so germination is quick, and weeds are slowing down. The catch is the cooling trajectory. Work backwards from your species’ days-to-germinate, then check that the soil will still be above the threshold for that whole stretch, plus a couple of weeks for the seedling to establish before growth slows at around 5°C. Our overseeding timing guide works through that arithmetic.
Spring sowing is slower to start and faces more weed competition, but the soil is warming, so a seed that germinates has the whole season ahead of it. Late April to early May is the usual advice in the UK, and in a cold spring it is too early. The threshold tells you when.
How to know when your soil is ready
- Look up your location on the soil temperature page and find when the 6cm reading holds at or above 8°C for five consecutive days (12°C if the mix is mostly meadow grass).
- Rake the surface so seed meets soil.
- Sow into the window that opens, and keep the surface moist until emergence.
How long does grass seed take to grow after that? Count the species row above from the day the threshold holds, not from the day the bag went down.
FAQ
Will grass seed germinate at 5°C? Effectively no. Cool-season species sit dormant below their thresholds, and Penn State Extension places reliable germination from about 8°C for ryegrass and 10 to 12°C for fescues and bent. Seed sown at 5°C is not wasted outright, but it sits and waits, and it is exposed to birds, washout and rot while it waits.
Should I cover the seed after sowing? A light covering of compost or topsoil helps hold moisture and hide the seed from birds, and it is standard in University of Minnesota Extension’s seeding guidance. More than about 1cm of cover and the emerging seedling burns through its reserves before it reaches light.
How soon can I mow a new lawn? Once the seedlings are established rather than a fixed number of days. The first cut discussion is in our first cut of the year guide: cut when the grass is growing and the ground takes a mower, at the highest setting.
We built mowdar for exactly this problem: enter your location and the soil temperature forecast shows when the threshold dates arrive, and the mow forecast shows the growth that follows. If you are still deciding what to sow, start with the species guide.