3 Cubic Metres of Mulch Produced by a Stihl GHE 140 L from Hedge Trimmings

What 3 cubic metres of shredded hedge weighs

The Stihl GHE 140 L is an electric quiet shredder rated for branch material up to about 35 mm. It runs a geared roller that crushes and cuts the feedstock. Knife shredders use high-speed flails; the GHE 140 L leaves a different chip, with bruised fibres and splayed ends.

Fresh beech and privet trimmings usually carry moisture north of 50 per cent. Three cubic metres of loose chip therefore weighs far more than the size of the heap suggests. Green hedge material at that moisture commonly settles somewhere between 250 and 400 kg per cubic metre, so a full afternoon cut can leave close to a tonne of wet chip to move by barrow.

Wet, dense, nitrogen-rich green chip packs down fast. Heaped more than about 40 cm deep and left alone, it can turn anaerobic. The roller damage exposes more surface area, which helps decomposition once air is present, but the same wet mass can slump into a sour heap if it has no structure. Straight from the chute, the material has three possible routes: hot pile, thin surface mulch, or a split between several uses.

Sorting the shredder output without overworking it

Separate the run into two rough grades as it comes away from the machine. The finer fraction, made up of crushed leaf and soft privet growth, is high in nitrogen and can break down in weeks. The woody beech ends are carbon-heavy and slow.

A hot compost pile works best around 25 to 30 parts carbon to one part nitrogen. Fresh green hedge chip alone is much greener, often closer to 15 or 20 to one, which is why an all-green heap becomes slimy silage. The woody beech chip from the GHE 140 L helps correct that imbalance and opens air spaces through the wetter material.

The HOTBIN composter is built for steady green input with structure mixed through it. Its insulated ABS walls hold a working temperature of 40 to 60 degrees Celsius, and the unit needs a bulking agent to keep air channels open. Mix roughly one part shredded corrugated card or coarse woody chip into every two parts green material, and keep the internal probe reading above 40. A domestic HOTBIN may process about 5 litres of fresh input a day at capacity, so three cubic metres from one hedge cut exceeds what it can take in a single batch.

Raised beds can take the coarse chip immediately as a surface mulch. A 5 to 7 cm layer over the bed surface suppresses weed germination, moderates soil temperature, and feeds the fungal side of the soil food web as it breaks down from below. Keep it a few centimetres away from perennial crowns and vegetable stems. Surface microbes will draw nitrogen from the top few millimetres of soil as they colonise woody chip, while the large nitrogen draw happens when raw chip is mixed down through the soil profile.

Building a hot pile from the coarse fraction

Most of a three-cubic-metre hedge cut belongs in a freestanding hot pile. The size requirement is physical: a thermophilic pile needs enough mass to insulate its core. A heap under about one cubic metre loses heat too quickly to sustain the 55 to 65 degree range where weed seeds and pathogens die off. One cubic metre is the practical floor. A full three cubic metres, built in one go with the right blend, will run hotter and longer than three small heaps.

Blend as you build and avoid thick strata. Mix green privet and leaf with woody beech and, if available, autumn leaves or straw to lift the carbon fraction. Water each barrowload as it goes on until the material feels like a wrung-out cloth, with no dripping. A dry pile never heats properly.

Push a compost thermometer with a 50 cm stem into the core. If the mix and moisture are right, the reading should climb within 48 hours. The first peak often arrives after four or five days.

Turn the heap when that core temperature peaks and begins to fall. Forking the pile moves cooler outer material into the hot centre and brings oxygen back into the mass, which usually triggers a second heat spike. Three or four turns over five to six weeks can take a well-built pile from raw chip to a coarse, dark, earthy crumb.

The beech ends will still be visible after the first cycle. Sieve them out and feed them into the next pile as a starter. Those fragments hold structure, air spaces, and an active fungal population.

Smell tells you a lot before the thermometer confirms it. An aerobic pile smells of warm earth and mushrooms. A sharp ammonia note means excess nitrogen and poor air movement, so fork in more woody chip and turn the heap. A sour, sulphurous, silage reek points to an anaerobic wet pocket, the common failure when green hedge chip is stacked too wet and too dense. Open the mass, add coarse woody structure, and turn it again.

Bokashi for wet fines

The softest privet growth and any grass clippings caught in the cut are often too wet and fine for a coarse pile. A bokashi bucket uses anaerobic fermentation: bran inoculated with lactic-acid bacteria pickles the material in a sealed 20 litre bucket over two weeks, producing a pre-digested ferment that can be buried in a bed or placed at the base of the next hot pile, where it breaks down within days.

Turning screened compost into lawn dressing

Overseeding a worn lawn depends on seed-to-soil contact, and the sieved compost fraction is useful here. Scarify out dead thatch first. Then run a hollow-tine aerator through the compacted sward so it pulls cores and leaves holes for air, water, and fresh root growth.

A fine, screened compost from the hot pile, passed through a 10 mm riddle, makes a workable top dressing. Brush it into the aeration holes at around 2 to 3 kg per square metre. Broadcast a hard-wearing perennial ryegrass and fescue seed mix across the dressed surface at roughly 25 to 35 grams per square metre for overseeding, water it in, and keep the surface damp through germination.

Moss is tied to the same tired-lawn conditions: compaction, waterlogging, shade, and acidity. Top dressing cannot cure it while drainage remains poor. Hollow-tine aeration relieves compaction and lets water move down through the profile instead of sitting on the surface where moss colonises.

Sulphate of iron blackens existing moss within days so it can be raked out, but iron only buys time. Without aeration and the improved surface drainage that follows, moss returns the next wet autumn. Keep coarse woody chip off the sward itself: chip mulch belongs on beds and around trees, while spread over grass it smothers the plants and ties up surface nitrogen.

The maths on a full afternoon

For a single three-cubic-metre cut, a workable split is two cubic metres of coarse woody-and-mixed material and one cubic metre of soft green fines. The two cubic metres of coarse chip build one respectable hot pile. After six weeks and four turns, that pile can shrink by more than half to under a cubic metre of usable compost. Perhaps 200 to 300 litres will pass a 10 mm riddle for lawn dressing, with the rest going back to beds as a coarse amendment. The soft cubic metre splits between a slow trickle into the HOTBIN and a couple of bokashi buckets.

Fresh shredded hedge loses volume quickly. Water evaporates, carbon leaves through microbial respiration, and the chip collapses as its structure breaks down. A hot pile routinely loses 50 to 70 per cent of its starting volume, so the tonne of wet chip produced in an afternoon becomes a few hundred litres of finished material over the following two months. The woody beech fragments that resist the first cycle are still sitting in the sieve, ready to carry structure and fungal inoculant into another heap.