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The goal of composting horse manure is to break it down into material that’s more beneficial to soil and plants and eliminate less desirable elements.
Proper composting generates enough heat to kill or greatly diminish worm eggs, fly larvae, pathogens and weed seeds. Killing worms and flies is important if you’re spreading manure on horse pastures. Killing pathogens (organisms capable of producing an infection or disease) is extremely important if manure is going on vegetable gardens or crops.
Check local regulations (your cooperative extension office is a great place to start) and site your compost pile (or pile system) properly. Generally it’s mandatory for drainage or run-off not to impact a water supply.
Maintaining airflow throughout the compost pile is key for preventing odors, achieving high temperatures, and completing the composting process in the shortest time. Small piles will have natural airflow but larger ones will be need to be aerated and/or turned.
For farms with 1-5 horses, a three bin “passive” composting system is ideal. One bin holds daily stall waste, the second bin is full and in the composting stage, and the third bin is for finished compost to be removed and used at your convenience. These can be quite simple to more elaborate:
Monitor the temperature. Compost needs to be hot enough to kill the undesirable factors, but overheating can kill many of the beneficial organisms needed for decomposition. Ideally the pile will reach temps of 120°F – 160°F for several weeks and then naturally cool down. Manage moisture in your compost pile(s). You don’t want it to become too soggy, which will cause it to smell and not decompose properly, or too dry. Keep it covered and only add water as needed. Minimize the amount of bedding in the pile. Straw, wood chips, shavings or sawdust (all are high in carbon) will slow down the composting process or even cause it not to complete. When added to the soil, high-carbon compost can also cause nitrogen deficiency in plants and turn their leaves yellow.
Compost should “cure” for at least a couple of weeks before use (ideally 1-3 mo. in summer and 3-6 mo. in winter). You’ll know you’re finished composting horse manure when it’s at the ambient temperature and is a crumbly, evenly textured, earthy-smelling, dark material that looks like commercial potting soil.
The easiest and best way to use composted horse manure is of course to spread it with a Millcreek manure spreader! Again, always check local regulations before spreading manure anywhere (composted or not).