9 Step Lawn Scarifying Routine with a Stihl RLA 240 on a 100-Square-Metre Plot

Set the depth dial before you charge the battery. The RLA 240 carries a five-position height adjuster on the handle, and for a first scarify on an established lawn the blade tips should only graze the soil surface rather than bite 5 mm into it. With an AK 30 pack, the machine gives roughly 20 minutes of continuous work, enough for one 100 m2 pass with a little margin. A deeper setting tears living grass crowns and can leave bare patches that need six to eight weeks to recover. Blade depth and moss content decide the job before the motor ever starts.

Mow to roughly 20 mm two days before scarifying. Long grass winds around the blades and can stall the motor, which on a battery machine means the thermal cutout may trip while the unit cools. A Stihl RMA cordless mower on its second-lowest notch gets close to that height without scalping the surface.

Moss volume sets the timetable

Spring and autumn are the usual scarifying windows, and they work as a starting point. The real trigger on any given lawn is the load of moss and thatch sitting in the sward, and that load swings sharply between a shaded north-facing plot and an open south-facing one.

A heavily mossed 100 m2 lawn produces an enormous volume of debris, easily many barrow loads in a single session, with the raking sometimes outlasting the scarifying itself. A lightly thatched lawn of the same size leaves only a fraction of that. The gap changes how much you rake, how often you stop, and whether a second battery is worth keeping on hand.

Moss takes hold where grass is already weak. Compacted soil, low pH, shade, and poor drainage all favour it. If a cheap soil probe reads below pH 5.5, moss will likely return within a season if scarifying is the only treatment, because the condition that favoured it has stayed in place.

An ericaceous-style acid correction is the wrong move here. Grass wants the pH moving upward. Garden lime applied in late winter, at the bag rate for your reading, nudges the soil toward pH 6.0 to 6.5, where ryegrass and fescue compete better against moss.

Test pH first. Treat visible moss with a sulphate of iron product about two weeks before scarifying so it blackens and dies, then lift the dead material with the machine. Green, wet moss smears into the surface and clogs the tines, while blackened moss breaks away far more readily. Skip the kill step and the number of passes can roughly double, because living moss binds to the tines.

Working width, pace, and battery margin

A 34 cm cutting width does not clear 100 m2 in a tidy set of under 30 straight runs. Each lane needs about 3 to 4 cm of overlap to avoid uncut strips, and few real lawns are plain rectangles. On a square plot, budget around 32 to 35 passes, with extra travel where beds, edges, and paths interrupt the route.

Work in one direction first, say north to south, at about one metre every two seconds. Pace matters more than it looks: hurry and the blades skim over the material they should be lifting, dawdle and they sit in one spot long enough to gouge the surface. The RLA 240 weighs about 9 kg, so it is easy to lean on it without meaning to, and that pressure drives the blades deeper than the dial setting. Let the machine ride on its own weight.

For a more severe renovation, make a second set of passes at 90 degrees to the first, east to west. The crosshatch lifts thatch the first direction left behind and exposes far more soil, so it belongs on a lawn you plan to overseed. A single-direction freshen-up on a tidy lawn usually uses one AK 30 charge. A crosshatch renovation normally wants two charges or a spare pack, since the machine is effectively covering over 200 m2.

Collection is a separate job

The RLA 240 has no collection box. Every scrap of debris comes off by hand or with a spring-tine rake, and on a heavily mossed lawn the raking can take longer than the scarifying.

Reading the exposed soil and seeding the gaps

After the debris is cleared, a renovation pass can leave 20 to 40 percent of the surface as bare soil. That exposure is useful, because grass seed needs contact with soil to germinate. A thatch layer thicker than 10 mm blocks that contact entirely.

Overseed the same day while the soil is open. For a worn 100 m2 lawn, use a perennial ryegrass and fescue mix at 25 to 35 grams per square metre, which means buying 2.5 to 3.5 kg of seed. Spread half in one direction and half at 90 degrees to even out coverage. A drop spreader holds a steadier rate than hand broadcasting, where the edges tend to finish sparse.

Germination needs soil above about 8 to 10 degrees Celsius, which is why early autumn so often beats early spring in temperate gardens. The soil still holds summer warmth, rain comes more reliably, and the worst of the annual weed pressure has already passed. Spring overseeding can work too, though it competes with germinating annual weeds and needs watering through dry spells. A young seedling can fail after three or four dry days.

After seeding, apply a light top dressing of sieved loam or sandy lawn dressing at around 2 to 3 kg per square metre. It fills the deeper grooves and holds moisture against the seed. Rake it in lightly so the seed sits in the top 5 mm, then water with a fine rose if no rain is forecast within 24 hours.

Feeding recovery without scorching seedlings

Avoid a high-nitrogen summer feed on a freshly scarified and seeded lawn. A quick-release nitrogen product at full rate can burn germinating seed and push established grass into soft growth that competes hard with new seedlings. An autumn lawn feed, lower in nitrogen and higher in potassium and phosphorus, fits this timing because it hardens the existing sward against winter and supports root development in the seedlings.

Apply the autumn feed about a week after seeding, once the first green haze of germination shows. The bag rate is usually around 35 grams per square metre, or 3.5 kg across 100 m2. Water it in if rain has not arrived within two days, since dry granules left on leaf blades can scorch them in sun.

Through the following spring, a balanced feed restarts growth. The first cut after overseeding should wait until the new grass reaches 50 to 60 mm, and then take only the top third. Cutting too short can pull shallow-rooted seedlings out completely. Keep the mower high for the first three cuts and lower it gradually.

When scarifying should wait

A lawn under a year old, laid as turf or seeded last season, should not be scarified. Its root system has not knitted into the soil, and the tines can lift the sward in sheets. Wait until it has survived a full mowing season.

Drought-stressed lawns in midsummer are another to leave alone. Scarifying a brown dormant lawn in July tears crowns that are barely holding on and have no moisture for recovery. Grass that looks dead is often only dormant and can green up with rain, while scarifying removes much of that chance. Wait for active growth and soil that is moist without being waterlogged, which on many plots points to September or late March.

Heavy moss combined with waterlogging is the difficult one. Scarifying clears the moss, but it does nothing for the drainage that caused the growth, so the moss can return by the next wet season. On those lawns, hollow-tine aeration and a sand-based top dressing should come before the scarifier, because clearing moss from ground that keeps inviting it back becomes an annual chore.

A 100 m2 example with one charge

Take a 10 m by 10 m lawn, moderately thatched and without heavy moss. Use one AK 30 pack and set the blades on the second notch. At one metre every two seconds, with 34 cm passes and 4 cm of overlap, the cutting line totals roughly 333 metres. That is about 11 minutes of motor time, leaving margin within the 20-minute runtime for stops to clear the tines.

Debris from that pass fills three to five barrow loads. Seed at 30 g per m2 comes to 3 kg. Autumn feed at 35 g per m2 comes to 3.5 kg. Top dressing at 2.5 kg per m2 comes to 250 kg, which means ten to twelve 25 kg bags for a full dressing. Most lawns only need the worn patches dressed and use about a quarter of that.

The crosshatch second pass either earns its extra charge or it does not, and you can only tell after the first pass: some lawns have shed nearly all their loose thatch by then, while others still show a clear mat of material lying across the line the blades just travelled.