Composting horse manure — a step-by-step guide
Composting solves three problems at once: volume, parasites and flies. Provided the heap actually reaches sanitisation temperature — and without a thermometer you do not know that it has.
Composting cuts the volume of horse manure by 40–70% and kills parasite eggs and weed seeds — provided the inside of the heap reaches about 60°C and holds it for at least 30 minutes in every part of the material. In practice that means a heap at least 1.5 m across and high, moisture around 50%, and several turns. Finished compost takes anywhere from two weeks to six months depending on method.
Horse manure is treated by default as a problem to be hauled away. Yet the 8.5 tonnes one horse produces in a year contain roughly 46 kg of nitrogen, 20 kg of phosphorus as P₂O₅ and 35 kg of potassium as K₂O. Composting raises the value of that material, but more importantly it solves three practical problems at once: volume, parasites and flies. This guide covers how to do it properly, and what not to do.
Why compost
| Effect | What it changes in practice |
|---|---|
| Volume down 40–70% | fewer skip collections, smaller storage area required |
| Core temperature about 60°C | destroys parasite eggs, fly larvae and weed seeds |
| Nitrogen stabilised | nutrients release slowly, the material does not scorch plants |
| No odour | a properly run heap smells of earth, not ammonia |
| Market value | compost can be sold or given away on good terms; raw manure often has to be paid away |
The second line is the most undervalued. Eggs of equine gastrointestinal parasites — strongyles, ascarids — survive in the environment for weeks, and in favourable conditions months. The common practice of spreading fresh manure thinly across pasture, in the belief that sun will dry it out, in fact increases the risk of reinfection, because it distributes eggs across the whole grazing area. Composting is the only method that solves this thermally.
How it works: four parameters
1. Carbon to nitrogen ratio (C:N)
Micro-organisms need carbon for fuel and nitrogen for building material. The optimum is 25 to 30 parts carbon to one part nitrogen. Horse faeces alone sit at roughly 20–25, slightly short of carbon; bedding supplies the excess. Manure with straw lands close to the optimum almost automatically, while manure heavy with sawdust is often too carbon-rich and breaks down slowly.
The heap smells of ammonia — too much nitrogen; add carbon material such as straw, shavings or shredded woody prunings. The heap will not heat despite adequate moisture and size — too much carbon or not enough oxygen; turn it, and consider adding fresh faeces.
2. Moisture
Target about 50%. The squeeze test: a handful should hold its shape and leave moisture on your palm without dripping. Too dry and the process stalls. Too wet and the heap turns anaerobic, smells, and never reaches temperature.
3. Oxygen
This is the most common point of failure. Without oxygen there is no aerobic decomposition, and without that there is no heat. Oxygen is supplied either by turning the heap or by passive aeration through perforated pipes laid in the base.
4. Heap size
The heap has to be big enough to hold heat in its core — at least 1.5 m wide and high. Too small and it never reaches sanitisation temperature. Too large, above roughly 2.5 m high, and it compacts under its own weight and loses air in the middle.
The temperature curve
| Phase | Temperature | Duration | What happens |
|---|---|---|---|
| Start-up | 20–40°C | 1–3 days | micro-organisms multiply |
| Thermophilic | 55–70°C | 1–3 weeks | sanitisation: parasites and seeds die |
| Maturation | 30–45°C | weeks | tougher fractions break down |
| Stabilisation | ambient | — | compost ready to use |
The sanitisation threshold is about 60°C held for at least 30 minutes — but reached in every part of the material. The core heats most; the edges stay cool. That is why turning is not only about aeration: it moves material from the cold outside into the hot centre. Without at least two or three turns, part of the manure never passes sanitisation.
Above 70°C the process begins to inhibit itself and beneficial organisms die off too. If the thermometer reads higher, turn the heap and consider making it smaller.
- A compost thermometer with a 90–100 cm probe — a few hundred euros, and without it you are running the process blind.
- A loader or tractor with forks for turning; beyond small volumes it cannot be done by hand.
- A tarpaulin or permeable geotextile — keeps autumn rain out without cutting off air.
Three methods to choose from
| Method | Time to finished compost | Labour | Who it suits |
|---|---|---|---|
| Static heap, no turning | 6–24 months | minimal | yards with space and no time pressure |
| Turned windrow | 2–6 months | moderate, needs machinery | the standard for most stables |
| Forced-aeration bays | 2–8 weeks | low once built | large yards, limited space |
The most common organisational mistake is one large heap with fresh material added daily. Such a heap is never finished, because the clock restarts with the last barrow tipped on it. The fix is a three-bay system: one filling, one maturing, one ready for collection. It takes more space, but it is the only way to end up with compost rather than perpetually fresh manure.
Composting and the rules
Composting does not remove the requirement for compliant manure storage. A composting pad used as permanent storage still needs an impermeable base and leachate capture. Where solid manure is stored temporarily on farmland, the usual national conditions apply — a maximum period on one site, minimum distances from water, flat ground, and a waiting period before reusing the same spot. See the guide to storage under the Nitrates Directive.
The good news: cutting volume by 40–70% reduces the storage area you need. For a yard facing a decision about extending its slab, composting is sometimes cheaper than concrete.
What to do with finished compost
- Your own pasture and land. The simplest route. Mind the closed periods for manure application, and note that compost releases nitrogen more slowly than raw manure — it works longer but weaker at the start.
- Neighbouring farmers and growers. Compost is accepted far more readily than raw manure: it does not spread weeds, it does not smell and it spreads more evenly.
- Retail sale. A niche, but a real one — gardeners and allotment holders pay for bagged horse compost. It requires consistent quality and, where sold as a soil improver, compliance with the rules on placing such products on the market.
- Mushroom substrate. Industrial buyers have their own specifications for composition and moisture, but they take large, steady volumes.
Five common mistakes
- Adding fresh material to a maturing heap. It resets the process. Solve it with separate bays.
- Not measuring temperature. Without a thermometer you do not know whether sanitisation happened — and that is the main reason you are composting at all.
- A soaked heap in autumn. An uncovered heap after a week of rain turns anaerobic. A permeable cover solves it.
- A heap that is too small. Below 1.5 m, heat escapes faster than it is generated.
- Spreading fresh manure on pasture. The worst possible practice from a parasite point of view — it distributes eggs instead of destroying them.
Frequently asked questions
How long does composting horse manure take?
From two weeks to two years depending on method. A static heap with no turning needs 6–24 months, a regularly turned windrow 2–6 months, and a forced-aeration system produces finished compost in 2–8 weeks.
What temperature kills parasite eggs in manure?
About 60°C held for at least 30 minutes in every part of the material. Because the edges of a heap stay cool, two or three turns are needed to move outer material into the hot core.
How much does composting reduce manure volume?
By 40–70%. That translates directly into fewer skip collections and a smaller storage area.
Can fresh horse manure be spread on pasture?
It is not advisable. Gastrointestinal parasite eggs survive in the environment for weeks or months, and spreading thinly distributes them across the whole grazing area, raising the risk of reinfection. Only compost that has been through the thermophilic phase is safe.
Does composting remove the need for a manure slab?
No. Permanent storage of manure, composted or not, needs an impermeable base and leachate capture. Composting does reduce the required capacity, because it cuts volume by 40–70%.
Why is my heap not heating up?
The usual causes are insufficient size (below 1.5 m wide and high), low moisture, lack of oxygen in compacted material, or excess carbon where there is a lot of sawdust. Start by turning the heap and checking moisture with the squeeze test.
Sources
- Horse Stable Manure Management — Penn State Extension
- Manure Management Strategies for Horse Farms — Mad Barn
Last updated: 2026-09-20. Prepared by the team at Clever Equine Solutions sp. z o.o..