Sometimes. Horse manure makes excellent compost, but it has weed seeds that need heat to kill.
Why
Horse manure is high in nitrogen and mixed with straw. The straw and seeds mean a cool pile can grow weeds. A hot pile over several weeks kills most seeds.
Quick facts
| Carbon to nitrogen | About 25:1 to 30:1 |
|---|---|
| Hot pile | 1-3 months |
| Cold pile | 6-12 months |
| Worm bin | Sometimes · Aged manure only; watch for heat buildup. |
| Bokashi | No · Too bulky and dry for effective fermentation. |
| City green bin | Usually accepted in yard waste bins; check rules. |
| Prep | Age or hot compost to kill weed seeds and pathogens. |
| Mix with | Mix with high-carbon brown materials if bedding is low. |
| Pest risk | Low · Can attract flies; cover with carbon layers. |
How to compost horse manure
- Mix the manure with dry leaves or wood chips to balance nitrogen.
- Build the pile at least 1 metre (3 feet) tall so it heats up.
- Turn it every week or two to kill weed seeds.
How much horse manure can you add to compost?
You can incorporate horse manure as your primary nitrogen source, but it should generally make up no more than 25 to 30 percent of your total pile volume. Always pair it with a generous amount of carbon-rich browns like dried leaves, straw, or shredded cardboard at a ratio of three parts brown to one part manure. If the pile develops a strong ammonia smell or becomes slimy and compacted, you have likely added too much manure and need to increase your carbon inputs.
Which types of horse manure can you compost?
- Stabled manure with bedding: Yes. This is the ideal form because the mixed-in straw or wood shavings already provide the necessary carbon balance.
- Pure manure without bedding: Sometimes. This is very high in nitrogen and will likely become anaerobic and smelly unless you manually add significant amounts of dry carbon materials.
- Manure from horses on deworming medication: Sometimes. Chemical residues can persist and potentially harm beneficial soil organisms like earthworms, so it is best to age this material for a full year.
Watch out for
- Don't use manure with herbicide residue, which can damage vegetable gardens.
- Check whether the horse was treated with wormers or other chemicals.
- Cool piles will sprout weeds.
What to do instead
- Let manure age for a year before using it.
- Give it to a local garden club or farm.
Troubleshooting horse manure in compost
- The pile develops a strong, pungent ammonia odor. This indicates the pile is too nitrogen-rich and lacks oxygen; turn the pile immediately and add a thick layer of dry straw or wood chips.
- The pile is matted and prevents water from penetrating. Break up the clumps with a pitchfork and mix in coarser carbon materials like woody twigs or dry leaves to improve aeration.
- Persistent weed growth in the finished compost. Your pile likely did not reach the necessary 130 to 150 degrees Fahrenheit; ensure the pile is at least one cubic metre and turn it more frequently.
Myths about composting horse manure
- Myth: Horse manure is already composted because it has been sitting in the field. Truth: Manure sitting in a field is just aging; true composting requires the specific moisture, oxygen, and heat levels achieved through active pile management.
- Myth: All horse manure is organic and safe for vegetable gardens. Truth: Many horses are treated with herbicides through their hay or medications that can leave persistent residues in the manure, potentially stunting sensitive crops like tomatoes.
Can horse manure go in a green bin or recycling?
Most municipal green waste programs do not accept horse manure in curbside bins because it is classified as agricultural waste rather than household food scraps. Some facilities may accept it at dedicated drop-off sites, but you must check your local waste management guidelines first. Always remove any plastic twine, baling wire, or non-compostable debris from the manure before attempting to transport it to a facility, as these contaminants are strictly prohibited in industrial composting streams.
Does composting horse manure attract pests?
Fresh horse manure can attract pests such as flies, rodents, and scavenging animals due to its strong natural odor and the presence of undigested grains or straw. While the manure itself is mostly fiber and digested forage, the scent draws insects looking to lay eggs or feed. Proper management, such as maintaining a hot compost pile and covering fresh additions with a thick layer of carbon materials, is essential to minimize unwanted visitors around your compost area.
- Cover fresh horse manure immediately with a layer of dry leaves or wood chips.
- Maintain a sufficiently large pile size to ensure proper internal heating that deters pests.
- Turn the pile regularly to discourage insects from breeding in the material.
- Ensure the composting area is kept tidy and avoid adding food scraps to manure-heavy piles.
Common questions
Can I compost horse poop?
Yes, in a hot pile. Build it big and turn it often.
Why does horse manure grow weeds?
Horses eat grass and seeds that survive in the manure. Heat kills most of them.
Is horse manure safe for vegetables?
Yes, once it's well composted and there are no herbicide residues.
Is horse manure biodegradable?
Yes. It breaks down into rich soil.
Rules vary by town and by composting method. When in doubt, check with your local composting or waste program.