You either have a horse or know someone who does and you want to use it as organic fertilizer in your garden. Fresh horse manure not only contains the possibility of introducing more weeds into your soil, but, more importantly, its nitrogen content is too high and rich for your plants and will burn and kill them. To effectively use horse manure for your fertilizer you need to let it breakdown. Only then is it a wonderful supplement to your soil.
Make a Compost Pile
Pile your horse manure in one area. Your manure may have shavings, straw or sawdust mixed in, which will help in the decomposition.
Mix organic matter such as leaves, grass clippings, and kitchen scraps into the horse manure pile.
Spray the horse manure and organic matter with water. Keeping your compost consistently moist, not soggy, is essential for rapid decomposition and break down of the horse manure. Monitor the moisture of your pile and spray the pile with water as needed to maintain a consistent moisture level.
Aerate the compost pile after a few weeks by either turning over the pile with a pitchfork or, for larger compost piles, use a tractor with a front loader. The combination of organic matter and air will speed the decomposition your compost pile. Additionally, by stirring up your compost, you will more evenly distribute the decomposition so there is less of a chance of a pocket of cooler non-decomposed matter remaining within your compost pile. Repeat this aeration, or stirring, of your compost pile every few weeks for the next two or three months.