Yes, horse manure absolutely can be used as compost safely, provided it is properly managed and composted correctly. Raw, uncomposted horse manure should never be applied directly to gardens, especially when growing vegetables, due to potential health risks and nutrient burn. The process of horse manure composting transforms this rich material into safe, beneficial soil amendment.
Why Gardeners Love Horse Manure
Horse manure is a gardener’s secret weapon. It offers many advantages when turned into quality compost. People often ask about using horse manure for garden plots because it works so well.
Benefits of Using Horse Manure
When prepared right, manure adds vital elements back into your soil. Here are the main perks:
- Nutrient Boost: Horse manure is rich in nitrogen, phosphorus, and potassium (NPK). These are plant food.
- Soil Structure Improvement: Compost helps heavy clay soil drain better. It also helps sandy soil hold water.
- Microbe Activity: Compost introduces helpful soil microbes. These tiny helpers break down organic matter. They make nutrients available to your plants.
- pH Balancing: Well-rotted manure tends to have a neutral pH. This is good for most garden plants.
- Water Retention: Manure compost acts like a sponge. It keeps soil moist for longer periods. This means less frequent watering.
Differences Between Horse Manure and Other Animal Manures
Not all manure is the same. Horses are non-ruminants. This means their digestive systems process food differently than cows or sheep.
| Manure Type | Key Difference | Nitrogen Level (Raw) |
|---|---|---|
| Horse | Eats a lot of high-fiber, low-protein feed. | Moderate to High |
| Cow | Ruminant; manure is very wet and breaks down slowly. | Low |
| Chicken | Very high in nitrogen; breaks down fast, easy to burn plants. | Very High |
Because horses eat a high-fiber diet, their manure breaks down relatively quickly in a compost pile. This makes composting horse manure easier for beginners.
The Critical Role of Bedding in Horse Manure Composting
When you collect manure from a stable, you almost never get just pure manure. It always comes mixed with bedding material. This bedding is crucial to the success of your compost.
Common Bedding Materials
The type of bedding used affects the carbon-to-nitrogen ratio (C:N ratio) of your pile. This ratio is the key to fast, hot composting.
- Straw: This is the best choice. Straw is high in carbon. It balances the high nitrogen in the manure well.
- Shavings (Wood): Wood shavings, like pine or cedar, are very high in carbon. They slow down decomposition. They need more nitrogen added to heat up properly.
- Pelleted Bedding: These absorb a lot of moisture. They can make the pile too dense if not managed.
Composting Bedding with Horse Manure
A good C:N ratio for fast horse manure composting is around 25:1 to 30:1.
- Manure is nitrogen-rich (low C:N).
- Bedding (especially straw) is carbon-rich (high C:N).
Mixing them helps create the perfect environment for the microbes that heat up the pile. Aim for roughly equal parts, by volume, of bedding and manure. If the pile is mostly manure, add carbon materials like dried leaves or shredded paper. If it is mostly wood shavings, add coffee grounds or grass clippings (nitrogen sources).
The Dangers of Raw Horse Manure Compost
This is the most important part of safe usage. Dangers of raw horse manure compost are real if you skip the heating phase.
Weed Seeds
Horses often eat hay contaminated with weed seeds. If you skip hot composting, these seeds survive. When you spread raw manure, you plant weeds all over your garden. Hot composting (reaching 130°F to 160°F) kills most weed seeds.
Pathogens and Parasites
Raw manure can carry pathogens like E. coli or Salmonella. It might also contain strong worm eggs or parasites from the horse. Pathogens are killed when the compost pile gets hot enough for a long enough time. This thermal process sterilizes the material.
Nitrogen Burn
Fresh manure is very high in quick-release nitrogen. If you put it near plant roots, the high salt content can draw water out of the roots. This “burns” the plants. Aged horse manure for soil has stabilized these nutrients, making them slow-release and safe.
Mastering the Horse Manure Composting Process
Effective composting horse manure requires attention to four main factors: volume, moisture, aeration, and temperature.
Setting Up the Compost Pile
To kill weed seeds and pathogens, you need a pile that heats up well.
- Size Matters: The pile should be at least 3 feet by 3 feet by 3 feet (one cubic yard). This size allows the center mass to insulate itself and reach high temperatures.
- Layering: Layering your greens (manure/nitrogen) and browns (straw/carbon) like a lasagna helps achieve a good mix. Then, turn the pile thoroughly to mix everything well.
- Moisture Check: The pile should feel like a wrung-out sponge—damp but not dripping. Water the pile if it seems dry before starting.
Temperature Management: The Key to Safety
Temperature dictates how fast the process goes and how safe the final product is.
| Temperature Range | Activity Level | Purpose |
|---|---|---|
| Below 100°F (38°C) | Slow activity. | Initial heating phase. |
| 131°F – 160°F (55°C – 71°C) | Pathogen and weed seed destruction occurs rapidly. | Active, effective composting phase. |
| Above 160°F (71°C) | Too hot; can kill beneficial microbes. | Needs turning to cool down slightly. |
You need a long-stemmed compost thermometer to monitor this. Turn the pile when the center temperature starts to drop below 130°F. Turning mixes the cooler outside material into the hot center. This ensures everything gets heated sufficiently.
How Long to Compost Horse Manure
The time required varies greatly based on management.
- Hot Composting (Managed Well): If you turn the pile regularly and keep the C:N ratio right, you might have finished compost in 2 to 4 months.
- Passive Composting (Set and Forget): If you just let it sit, it can take 6 months to over a year to fully break down. This passive method is less reliable for killing all weed seeds quickly.
Curing Time: Achieving Aged Horse Manure for Soil
Even after the pile stops heating, the compost is not quite ready. This final stage is called curing.
During curing, the sharp, earthy smell fades. The material turns dark brown, crumbly, and smells like rich earth. This slow process stabilizes the nutrients. The benefits of aged manure become fully apparent here—it won’t harm roots. Aim for at least one month of curing after the pile stops heating, or ideally, let it sit for 4-6 months total before heavy use.
Specific Uses for Horse Manure Compost in the Garden
Once you have safe, dark, crumbly compost, you can use it widely.
Composting Manure for Vegetables
Vegetable gardens have the highest risk from pathogens in raw manure. Therefore, it is essential to use only fully finished, cured compost on edible crops.
- Pre-Planting Amendment: Apply a 1 to 2-inch layer to garden beds in the fall or early spring. Till it lightly into the top 6 inches of soil. This allows the aged horse manure for soil to fully integrate before planting.
- Side Dressing: Apply a thin layer around established plants mid-season to provide a slow nutrient boost. Do not pile it directly against the stems.
Using Finished Compost for Non-Edibles
Flower beds, lawns, and perennial borders are more forgiving than vegetable plots. You can use compost that is slightly less refined here, though “hot-finished” compost is always best.
- Top Dressing Lawns: Spread a very thin layer (about half an inch) of fine compost over your lawn. Rake it in lightly. This improves soil structure and feeds the grass slowly.
- Potting Mix Component: Finished, fine compost can make up 20% to 30% of a homemade potting mix, improving water retention and feeding container plants.
The Importance of a “Cool” Product for Roots
When composting manure for vegetables, the goal is to ensure no ammonia smell remains. Ammonia is a sign of active decomposition. If you smell ammonia, the compost is still too “hot” or fresh. Finished compost smells like the forest floor.
Troubleshooting Common Horse Manure Composting Issues
Even with the best intentions, compost piles can sometimes act stubborn.
Pile Won’t Heat Up
If your pile stays cool, it usually means one of two things:
- Too Much Carbon (Browns): If you used too much straw or wood shavings, the microbes lack nitrogen to work. Fix: Add high-nitrogen “greens,” such as fresh grass clippings, manure, or coffee grounds. Mix well.
- Too Dry: Microbes need moisture. Fix: Water the pile thoroughly while turning it.
Pile Smells Like Ammonia
This is a classic sign of too much nitrogen. The excess nitrogen is turning into ammonia gas and escaping.
Fix: Immediately turn the pile and mix in high-carbon “browns,” like shredded dry leaves, sawdust, or plain straw. This balances the C:N ratio and locks the nitrogen back into the system where microbes can use it.
Pile is Slimy and Smelly (Rotting)
This usually means the pile is too wet and lacks air (poor aeration). Anaerobic (oxygen-free) bacteria take over, causing foul odors.
Fix: Stop adding wet material. Turn the pile aggressively to introduce air. You may need to mix in dry, bulky brown materials like shredded cardboard or straw to absorb excess water and create air pockets.
Dealing with Pine Shavings
If you use wood shavings, remember they are very slow to break down because they have a very high carbon content. This high carbon ties up available nitrogen temporarily.
Fix: When using a lot of wood shavings, you must add a significant nitrogen boost—more manure, compost starter, or blood meal—to kickstart the decomposition. Be patient; this material takes longer to break down into usable compost.
Safety Checklist Before Applying Manure Compost
To ensure you maximize the benefits of using horse manure safely, run through this final checklist.
- Visual Test: Is the material dark brown or black?
- Texture Test: Is it crumbly, like rich soil? Can you no longer identify the original straw or shavings?
- Smell Test: Does it smell earthy? If it smells sharp, sour, or like ammonia, it needs more time or turning.
- Temperature Test: Has the pile stayed cool for several weeks after the last significant turn?
If the answer is yes to all four, your product is finished, safe compost ready for the garden.
Frequently Asked Questions (FAQ) About Horse Manure Compost
Q: Can I use fresh horse manure directly in my garden?
A: No. Do not use fresh manure directly on plants, especially vegetables. It must be composted first to kill pathogens, eliminate weed seeds, and stabilize the nutrients to prevent burning your plants.
Q: Do I have to worry about the horse’s deworming medication in the compost?
A: This is a valid concern. Some common dewormers (like Ivermectin) can be harmful to beneficial insects, like earthworms and dung beetles, if applied in raw or partially composted manure. The high heat of a properly managed compost pile (above 131°F for several days) usually breaks down these chemical residues. However, if you are concerned, or if you are using the compost on a very sensitive organic vegetable patch, cure the manure for a full year before using it.
Q: What is the best carbon source to mix with horse manure?
A: Straw is traditionally the best choice because it comes readily available at most stables and provides a good balance. Dried, fallen leaves, shredded newspaper (non-glossy), or sawdust (sparingly, due to high C content) also work well as carbon sources.
Q: Can I compost manure from a horse recently treated with antibiotics?
A: It is best to let manure from medicated animals sit for several months or cure for a full season before adding it to your active compost or garden. While heat generally degrades many common medications, prudence is key when dealing with edible crops.
Q: How long does it take for aged horse manure for soil to be ready?
A: Under ideal hot composting conditions, you can achieve finished compost in 2 to 4 months. However, allowing it to cure for an additional 2 to 4 months (totaling 4 to 8 months) results in truly aged horse manure for soil that is safer and more beneficial.