Sowing Grass Seed in Scotland: Timing, Prep and Aftercare for a New or Repaired Lawn

Grass seed germinatesA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition → when the soil is warm and moist enough, not on a calendar date. The standard windows are mid-spring and early autumn, and on Met Office temperatures both are narrower in Scotland than in the south of England. Sow when your own soil is reading above about 8°C and the seedbed is firm, fine and moist, and the seed will usually be up in seven to ten days.

What temperature grass seed needs

Two UK sources give different figures. Gardeners' World puts the minimum soil temperature at 8°C. The turf supplier Rolawn says typical daily temperatures need to be above 13°C for successful germination. The lower figure is the point where seed will start; the higher is a more conservative target for reliable, even germination. The RHS gives no temperature, only that the soil should be warm and moist with weather neither too cold nor too hot, and germination takes seven to ten days. Measuring your own ground settles it.

A basic soil thermometer pushed in to about 5 to 7.5cm, read at the same time each morning for several days running, tells you more than a regional table. A sheltered, south-facing bed can run warmer than the nearest weather station, and an exposed, shaded or north-facing one cooler.

The Scottish temperature gap

Met Office long-term averages for 1991 to 2020 show how much later Scotland reaches those figures. The table gives mean monthly air temperature, worked out as the average of the mean daily maximum and minimum. Soil follows air temperature, a little behind, so treat it as a guide to the window and not a reading for your garden.

Against the 8°C floor, Heathrow clears it in April and Edinburgh and Glasgow only just do (8.2°C), so April is borderline in Scotland and May is the first comfortable month. In autumn, September is warm everywhere, but October has fallen to about 9.7°C in Scotland while Heathrow still has 12.3°C. Against the 13°C target, the Scottish stations manage it in September only narrowly (13.1°C at Edinburgh, 12.9°C at Glasgow) and do not reach it in March, April or May. Spring and autumn are still the right windows; they are narrower at both ends.

Edinburgh (Gogarbank) and Glasgow (Bishopton) are lowland stations, so this is a fair picture of the Central Belt. A Highland, upland or exposed garden will typically run cooler, and a sheltered town garden warmer. Altitude, aspect and shelter all shift the real date.

Ground that is still waterlogged from winter should not be sown whatever the temperature: seed needs air as well as warmth, and standing water will rot it. This matters more in the west. Annual rainfall is about 728mm at Edinburgh and 1,275mm on Tiree (Met Office, 1991 to 2020), so western gardens are likelier to be sodden when the spring window opens. If the lawn area drains slowly, fix that first: see fixing a waterlogged lawn on clay soil.

One thing works in Scotland's favour: summer days are longer. At the June solstice Edinburgh has about 17 hours 36 minutes of daylight against about 16 hours 38 minutes in London, so once the soil crosses the threshold, seedlings have more light to grow on.

When to sow in Scotland

• Spring: mid to late April into May, once the soil has had a real run of milder weather, rather than as soon as the calendar says March.
• Autumn: September, early October at the latest in most of lowland Scotland. October is already only just above the 8°C floor (about 9.7°C), and later than that germination becomes a race against falling soil temperature, with seedlings that may not establish before growth slows for winter.

Early autumn is usually the stronger choice where practical: the soil is at its warmest for the year, and there is usually less competition from weed seeds, many of which germinate in spring. Leave enough time either side for frost-free growing: the regional frost dates give the detail for your area. Sowing in high summer or deep winter is not recommended: the soil is too dry and hot in midsummer and too cold and dark in winter.

Choosing a mix and checking the soil

A shaded garden does better with a shade-tolerant fescue-heavy mix than a hard-wearing ryegrass blend, which performs poorly without good light. A mix marketed for damp or heavy ground is worth choosing if the site is on the wetter side once any drainage problem is fixed. Read the product description and use fine or turf-grade ryegrass mixes, since cheap seed can contain coarse agricultural ryegrass and weeds.

Grass grows best in slightly acidic to neutral soil, roughly pH 5.5 to 7. Scotland has higher shares of naturally acidic podzol and peat than Europe as a whole, concentrated in the Highlands and Southern Uplands, so a cheap pH test kit is worth using. If the soil is notably acidic, apply lime well before sowing so it has time to work in: the settling period below is a natural point to do it.

Preparing the seedbed

Seed needs firm, close contact with soil; a rough, loose surface leaves seed in air pockets where it dries out and dies.

1. Clear the ground. Dig out the roots of perennial weeds well ahead of sowing; roots left in place will out-compete new seedlings.
2. Break up compaction. Dig to about 20cm deep.
3. Improve poor soil. On light, fast-draining soil work in well-rotted manure or compost to help hold moisture.
4. Let it settle. Ideally leave the dug area for five to six weeks before sowing.
5. Firm it. Tread the area several times in different directions with small shuffling steps.
6. Rake level. Rake thoroughly in various directions to a fine, crumb-textured seedbed (a tilthThe crumbly, fine texture of well-prepared soil, achieved by raking the surface, that small seeds are typically sown into. Full definition →) with no large lumps.
7. Feed, optionally. The RHS suggests raking in a general-purpose fertiliser at 70g per square metre before sowing.

To patch bare or thin areas in an existing lawn, the same principle applies on a smaller scale: rake the patch hard enough to break the surface and expose bare soil, work in a little topsoil or compost if it is compacted or poor, then sow and care for it as a mini version of a new lawn. Lawns are best repaired in spring or autumn, when the weather is damp and cool.

Sowing rate and technique

Use the weight per square metre printed on the packet: a fine fescue mix and a hard-wearing ryegrass mix are not sown at the same density. Divide the seed into two equal batches and sow one north-south and the other east-west for more even coverage.

Lightly rake the seed in so most of it is covered but not buried, then firm again lightly with the back of a rake or by treading. Avoid sowing on a windy day.

Watering a new sowing

Keep the seedbed moist but not waterlogged from sowing through establishment. Water gently with a fine rose or spray straight after sowing if rain is not forecast, and then every few days as needed so the surface never dries out. Seed that germinates and then dries out in its first days dies as surely as seed that never came up. A hard jet washes seed into clumps or off the patch, so a fine spray matters more than volume.

Protecting from birds, pets and wind

Birds take seed straight off the surface, and cats, dogs and foot traffic disturb the seedbed. Cover the area with horticultural fleeceA lightweight, breathable fabric laid or draped over plants to trap a little warmth and keep off frost, wind and some flying pests. Full definition → weighted down at the edges, or use bird-scaring tape on larger areas, and keep pets and people off until the grass is established.

If you would rather not cover the area, increasing the sowing rate by 50% compensates for bird losses, though it does nothing for pets or trampling. In an exposed or coastal garden, wind can drift loose seed before it roots, especially on light or sandy soil: firm the seed in well, choose a still day, and peg fleece down at the edges.

First cut

Start mowing when the new grass is about 5 to 7.5cm tall and the soil has been refirmed, taking off only about a third of the height. Ideally use a cylinder mower; otherwise set the highest cutting height your mower offers. Make sure the ground is firm enough that the mower does not tear up the young turf. If the first cut lands on a damp week, the guidance on mowing wet grass applies on top of the extra care young turf needs.

Troubleshooting poor or patchy germination

If nothing has come up two or three weeks after sowing, the likely causes are, roughly in order:

• Soil too cold. The most likely cause outside the spring and early-autumn windows in Scotland; the seed may be dormant, not dead. Check with a soil thermometer before resowing.
• Seedbed dried out. A single missed watering can kill seed that has started to germinate, which is the usual cause of patchy rather than total failure.
• Poor seed-to-soil contact. Seed on a crusted or loose surface germinates unevenly or not at all: check the firming and raking if a whole area has failed.
• Bird losses. Thin patches with no obvious pattern, especially near open ground, often point to birds.
• Leatherjackets or chafer grubs. These larvae feed on grass roots and can thin or kill patches from underneath. Birds probing the turf and patches that lift easily are the signs. Damp conditions favour leatherjacket survival, so it is worth checking first in the wetter west and after a wet autumn. Nematodes watered in are the control for leatherjackets, in September to early October when soil is moist and 12°C or above.
• Slugs. Damp soil that suits germination suits slugs, which graze new shoots at ground level. Thin, nibbled patches point here. Watering in the morning rather than evening and clearing nearby debris where they shelter help without chemicals.
• Sowing into waterlogged ground. Seed may have rotted rather than failed to germinate.

Where the cause looks like cold soil rather than a preparation fault, oversowing the same area once conditions warm up is usually better than re-digging.

Common questions

Sources