Learn / Composting methods

Windrow composting: making compost at scale.

A windrow is a long, narrow pile of organic waste, built in rows and turned regularly. It is the standard method for farms, estates, markets and municipalities that handle tonnes of waste rather than bucketfuls. It needs space, a plan for run-off and a way to turn the piles, and it rewards you with a lot of compost.

How to build one Selling compost

at a glance

The numbers that matter

A windrow is a heap composting system scaled up. The same biology applies. What changes is the size, the site, the equipment and the rules.

1.2–1.8 m a typical windrow height, and about 2.4 to 3.7 m wide. SOURCE: UNL EXTENSION G1315 (CONVERTED FROM FEET)

55°C for at least 15 days, with at least 5 turns, is the benchmark for killing pathogens in a windrow. SOURCE: US EPA 40 CFR PART 503

1 mo+ of curing after the hot phase, before the compost is finished. SOURCE: UNL EXTENSION G1315

is it right for you?

When windrows make sense

Windrows suit anyone with steady, large volumes of organic waste and enough open ground. Typical users are flower and vegetable farms, tea and coffee estates, livestock units, markets, schools and county waste programmes.

	Heap or bin	Windrow
Volume	Kitchen and garden waste, up to a few cubic metres.	Tonnes of material, delivered regularly.
Turning	By hand, with a fork.	Usually by machine, such as a front-end loader or a dedicated turner. A fork is only practical for short windrows.
Site	Any corner of a plot.	A planned, drained, ideally hard-surfaced pad.
Control	Judged by feel.	Temperature and moisture logged, turning scheduled.
Rules	Few.	Waste, odour, standards and licensing rules can apply, especially if you sell the compost.

Smaller scale? See heap composting or bin and barrel composting.

SOURCES: UNL EXTENSION G1315; COMPARISON SUMMARISED BY ESSENTIA KANAN

before you build

Choosing and preparing the site

Most windrow problems begin with the site, not the pile. Plan these things first.

A gentle slope. Aim for a slope of about 2 percent so water drains off the pad instead of pooling under the piles.
Divert run-off away. Keep rain water from higher ground out of the composting area with a drain or bund.
Catch what comes out. Water that runs through the piles (leachate) is strong and polluting. Direct it to a lined pond or tank, and never to a stream, borehole or well.
Keep your distance. Site the pad away from homes, water sources and the prevailing wind direction from neighbours.
Leave room for every stage. You need space for incoming material, the active windrows, the curing area and the finished compost store, plus room for machines to turn and manoeuvre.
A firm surface. Compacted soil, murram or concrete lets machines work in wet weather without churning up the ground.

SOURCES: EXTENSION.ORG, COMPOSTING SITE SELECTION AND LEACHATE MANAGEMENT; UNL EXTENSION G1315

building the windrow

Mix, shape, monitor

Plan the mixCombine nitrogen-rich “greens” (fresh crop waste, manure, vegetable trimmings) with carbon-rich “browns” (straw, dry stalks, sawdust, shredded prunings) so the blend lands near a carbon-to-nitrogen ratio of 25 to 30 parts carbon to 1 part nitrogen.
Shred and blendChop coarse material small. Mix the ingredients thoroughly before piling, because a bad mix is hard to fix once it is stacked.
Check the moistureAim for 50 to 60 percent moisture. A handful squeezed hard should release a drop or two of water and feel like a wrung-out sponge. Add water while you mix, not afterwards.
Shape the rowPile the material into a long row about 1.2 to 1.8 m high and 2.4 to 3.7 m wide, as your equipment allows. The pile should be big enough to hold heat and small enough to let air in.
Measure the heatPush a long-stem compost thermometer into the middle of the pile at several points along the row. Record the readings, and the date, every day or two.
Turn on a scheduleSee the next section. Turning mixes, aerates and moves cooler outer material into the hot centre.
CureWhen the pile stops reheating after a turn, let it rest for at least a month. Curing finishes the breakdown and stabilises the compost.

SOURCES: UNL EXTENSION G1315; FAO COMPOSTING GUIDANCE; CONVERTED FROM FEET WHERE NEEDED

heat and hygiene

Turning, temperature and safe compost

Temperature is how you steer a windrow and how you prove it is safe.

What you read	What it means	What to do
Around 55–60°C	The preferred hot phase. Microbes are working hard and pathogens are dying.	Keep it here. Turn on schedule.
Above about 63°C	Too hot. Useful microbes begin to suffer and the pile can slow.	Turn now to bring the temperature down.
Falls below about 40°C early on	The pile is short of air, water, nitrogen or size.	Check moisture and the mix, add nitrogen-rich material if needed, and turn.
No reheating after a turn	The hot phase is over.	Move the row to the curing area.

The pathogen benchmark.

For windrows, the US Environmental Protection Agency’s rule for treating sewage sludge (40 CFR Part 503) requires at least 55°C for at least 15 days, with at least five turns during that time. Five turns in 15 days works out to roughly one every three days. This is a US rule for biosolids, but it is widely used as a safe target for any windrow that handles manure or food waste.

Weed seeds need more heat than most pathogens, around 63°C, so a windrow that never gets properly hot will carry weeds onto your fields. Oxygen matters too. Keep it above about 5 percent in the pile, which is what regular turning is for.

SOURCES: US EPA 40 CFR PART 503; UNL EXTENSION G1315; FAO COMPOSTING GUIDANCE

a Kenyan example

Windrows on a Naivasha rose farm

Flower farms around Lake Naivasha produce large volumes of green waste. A 2024 study by de Nijs and colleagues followed windrow composting of this waste on a rose farm.

What they found

Windrow composting cut the waste volume by about 82 percent.
The finished compost had a carbon-to-nitrogen ratio of below 10, a sign of a stable product.
Using the compost was linked to yield gains of 3.2 to 4.7 percent.

What to watch

The researchers flagged pesticide residues as a concern. Flower farms spray heavily, and some chemicals can survive composting. Test compost made from treated crop waste before you apply it to food crops.

SOURCES: DE NIJS ET AL. (2024), WINDROW COMPOSTING OF GREEN WASTE ON A NAIVASHA ROSE FARM; UNIVERSITY OF AMSTERDAM THESIS (2025)

selling compost

Standards, labels and licences

Compost you use on your own land faces few rules. Compost you sell is a regulated fertiliser. Kenya’s organic fertiliser standard, KS 2290, sets the benchmark.

Check the version.

The figures below come from the 2023 draft of KS 2290 (third edition), as notified to the World Trade Organization. The final text may differ, so confirm the current requirements with the Kenya Bureau of Standards (KEBS) before you rely on them.

Parameter (solid organic fertiliser)	Draft KS 2290 limit
pH	5.5 to 8.5
Carbon-to-nitrogen ratio	25:1 or lower
Moisture	15 to 40 percent
Organic matter	20 to 70 percent
Nitrogen	More than 1 percent
Nitrogen + phosphorus + potassium	At least 3.5 percent by weight
Heavy metals (mg/kg)	Arsenic 10, cadmium 5, chromium 50, copper 300, lead 30, mercury 0.1, nickel 50
E. coli	1,000 colony-forming units per gram at most
Salmonella	None
General	Practically free from foul smell; free from plastics, stones, weed seeds and pesticide or antibiotic residues above allowed levels.

Two things surprise first-time sellers. The moisture limit means finished compost must be dried well below the 50 to 60 percent used during composting. And the nitrogen and total nutrient minimums are demanding: some compost made mainly from woody or low-nitrogen waste may fall short, so have a sample analysed early.

Labels

The draft requires clear labelling on every pack, including the product and brand name, net weight, batch number, producer’s name and address, nutrient content with the carbon-to-nitrogen ratio, organic matter and moisture, manufacture and expiry dates, instructions for use, ingredients and storage directions. It also restricts claims: you cannot call a product completely safe or non-toxic without verification, and benefit claims need data to support them.

Licences and permits

Under Kenya’s Waste Management Regulations (2006), operating a waste disposal site or plant needs a NEMA licence and any county licence, and the licence application form lists compost as one of the facility types. Moving waste on public roads needs a licensed transporter and approved vehicle. Fertiliser sales fall under the Fertilizers and Animal Foodstuffs Act (Cap 345). The rules that apply to your site depend on its size and what you handle, so speak to NEMA and your county before you build.

SOURCES: KS 2290:2023 DRAFT (THIRD EDITION), AS NOTIFIED TO THE WTO; ENVIRONMENTAL MANAGEMENT AND CO-ORDINATION (WASTE MANAGEMENT) REGULATIONS, 2006, REGS 7 AND 10 AND FORM IV (KENYA LAW)

when it goes wrong

What to look for and how to fix it

What you see or smell	What it means	What to do
Rotten or sewage smell	Too wet or too compacted, so air is cut off.	Turn, mix in dry coarse material such as straw, and fix drainage on the pad.
Ammonia smell	Too much nitrogen for the carbon.	Mix in more browns, then turn.
Never heats up	Too dry, too small, or too little nitrogen.	Add water while turning, enlarge the row, and add greens or manure.
Dry and whitish in places	Too dry.	Water while turning. Surface watering alone does not reach the middle.
Flies and rodents	Food waste exposed on the surface.	Bury fresh food waste in the centre of the row and cover it with a layer of dry material.
Pools of dark liquid	Leachate escaping the pile.	Check drainage and the collection tank. Add dry bulking material to the mix.
Plastic and glass in the finished compost	Contaminated feedstock.	Sort at the source, and screen the finished compost before bagging.

SOURCES: UNL EXTENSION G1315; EXTENSION.ORG

Questions people ask

How much waste do I need for a windrow?

Enough to build a row at least about 1.2 m high and 2.4 m wide, as that mass holds the heat. Anything smaller behaves like a heap.

Do I need a machine to turn it?

For long windrows, yes. A front-end loader works, and dedicated turners are faster. For short rows, a team with forks can manage, but frequent turning at scale is heavy work.

How long does a windrow take?

The hot phase runs for several weeks with regular turning. Add at least a month of curing. The exact time depends on your materials, moisture and how often you turn.

Can I compost manure and food waste together?

Yes, if the pile reaches and holds 55°C for the required time with enough turns. Keep a temperature log, as it is also your proof of safe compost.

Can I sell the compost?

Yes, but it is regulated. It should meet KS 2290, be labelled correctly, and come from a site that has the permits it needs. Do not market it as certified organic fertiliser without the relevant approvals.

Is compost from flower farm waste safe for food crops?

Not automatically. Pesticide residues can survive composting. Test the compost and trial it on a small area before wider use.

next step

Planning a windrow operation?

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