Horse manure is a nuisance to horse owners, veterinarians and those who board or care for horses, but has a legendary reputation for good among gardeners. While selling horse manure is good for horse lovers and gardeners alike, the process isn’t as simple as letting the manure sit and rot. Nonetheless, creating usable horse manure—and taking advantage of it in the garden—is easy.
Horse manure is often called “black gold” for the garden. According to the Gardener’s Network, it adds nutrients to the soil, including three all plants need in order to thrive: nitrogen, phosphorus and potassium. In addition, horse manure helps retain moisture in the soil and breaks up clay earth.
For those who care for horses, creating composted horse manure has additional benefits. Instead of letting manure sit in fetid, pest-attracting, polluting piles or paying someone to haul the manure away, they can sell manure to local gardeners.
Many gardeners think they can pile fresh horse manure in their gardens and reap benefits. Unfortunately, fresh manure is “hot”—meaning it’s high in nitrogen. If applied hot, it will injure or kill plants. In addition, fresh manure is full of weed seeds. Horse manure must be “hot composted” to prevent these problems.
How to Hot Compost Horse Manure
Build at least two compost bins on a high, level area. Bins can be made of wood slats and should measure at least 4’x8’x8’. Fill one bin at a time and cover them with a tarp to prevent the contents from becoming soggy. Add water as necessary to keep the manure damp. Turn the contents regularly to help speed the decomposition process, or reduce the need to turn the pile by hand by installing a few 5-foot tall PVC pipes in the centre of the bins. Drill holes all over these pipes to encourage air circulation in the bin. When the manure is evenly textured and looks like dark, crumbly soil, it’s ready to use. According to the University of Illinois Extension, properly composted horse manure is aged and ready to use in about one month.
How to Use Horse Manure
Once the gardener has aged, hot-composted manure in hand, it's easy to use. Before planting, till the manure into garden soil using a rototiller or spade. For established gardens, lay aged horse manure down like topdressing or mulch, spreading it evenly about 1 to 3 inches deep.
In addition to only buying hot composted horse manure, gardeners should take additional precautions when using manure in their gardens. First, do not allow horse manure to directly touch plant stems or trunks. Second, do not add horse manure to the garden every year or the soil will eventually contain too much magnesium, resulting in stunted, sickly plants. Finally, thoroughly wash all produce grown in horse manure before consuming.