Urban gardeners do not usually have the access to raw manure that their farming ancestors did. However, horses are still a popular pet and can be found in outlying areas, and horse manure is a nitrogen-rich gardener's delight if you know how to prepare and use it.
Where to Get It
Horse manure is easy to get in one of two ways. The first way is to buy it by the bag in prepared mixes at your garden center or hardware store. Another way to get horse manure is to buy it fresh off the farm. Find a local horse owner, stable or race track and ask the owner if she sells manure. You might even get a great deal from horse owners just looking for someone to haul it away. You bag it, and it's free. However, a drawback to fresh horse manure is it must be prepared properly to use on a garden.
Raw horse manure is hot. It can burn the tender leaves and stalks of plants if it gets too close. Even the juices traveling down toward the roots of plants with water can burn and destroy plant root systems. Even though it sounds like horse manure would be the last thing you'd want on your garden, when it is done correctly, none of the above applies, and it gives plants everything they need to thrive.
Horse manure is rich in nitrogen. Nitrogen is very effective, but it has to be aged to be safe. Horse manure needs to age in a compost pile. Hot composting works best because there are weeds and weed seeds in horse manure because the horses eat weeds along with grass. Heat kills those seeds and renders them impotent. Heat also kills any germs in the manure so it is safe to use for human food.
Prepare a three-sided compost bit with plenty of air holes, or spaces between the slat sides. Compost needs oxygen to develop. Pile manure into the contained area so that the bulk of it creates a high temperature inside its core. Insert a thermometer into the pile regularly until it reads 150 degrees F. Turn the pile every few days so that the heat is distributed to a new center and eventually the entire pile is processed. If you smell ammonia when you turn the pile it is too hot and needs to turn more often. A healthy compost pile has no perceivable odor. Keep the compost moist. If enough rain falls it will not need water. During dry spells sprinkle the compost enough to soak the top inch. The compost is ready when it is not hot anymore, and when you turn it no steam rises.
Cure the compost for at least a month after it is finished "cooking." Use compost to enrich the soil in the spring and fall. Till in a generous amount after harvesting at the end of the season so the manure overwinters in the soil. In the spring, spread another layer over the top of the garden area and mix well for a rich, thick planting solution. During the planting season, spread it evenly around plants and water thoroughly so that the juices of the manure soak into the ground at the base of the plants.