Most gardeners are familiar with compost made from excess plant materials such as leaves, grass clippings, garden trimmings and kitchen peelings. Piled up in a heap in a corner of the garden, kept moist and turned, this garden waste eventually turns into crumbly black soil gardeners call black gold.
Another source of black gold that is returning to favor is farm animal manures. Long before the advent of modern synthetic fertilizers in the 1930s and ’40s, animal manures were the main source of plant nutrition. As we return to sustainable and organic forms of gardening and farming, their use is coming back into practice.
Manures used in home gardens need to be from animals that eat only vegetable material including horses, cows, chickens, rabbits, goats, sheep and llamas. Animals such as pigs, dogs and cats are carnivores and can carry parasites and diseases that can transfer to humans.
The most common source of manure for the average gardener comes in bags purchased from the garden center. The manure, usually from cows or chickens, is aged to kill weed seeds and harmful bacteria, dried and then put in an easy-to-use bag ready for the garden.
Manures straight from the farm take a little more handling and processing. First and foremost, the manure should have been aged or composted for at least six months to a year before it is put in a garden. Fresh manures still contain salts and acids from the digestion process and can burn the plants they are put on. Composting fresh manure for a few months reduces these to acceptable levels. Aging also helps destroy weed seed, bacteria and other pathogens found in raw manures.
Manures often come mixed with straw or wood shaving bedding material that will need this time to break down. Lastly, aged manure isn’t quite as odiferous as the fresh stuff. This is especially important for chicken manure whose odor has been known to clear a neighborhood when brought in too fresh.
Animal manures have much lower levels of nitrogen, phosphorus and potassium than synthetic fertilizers and release it more slowly to the plants. Chicken and rabbit manure contain the highest levels of nitrogen followed by horse, cow and sheep. All have about the same percentage of phosphorus and potassium. Because cows are better at digesting weed seed completely, cow manure will have fewer weed seed hitchhikers than horse manure.
The best time to add manure to a garden is in the fall so it has the winter to finish aging and be ready for planting in the spring. Well-aged manures can be used as a top dressing during the growing season.
Finding farm manure can be as simple as asking a local farmer who has the appropriate animals or putting an ad in the paper or on Craigslist. Some farmers will charge for it, others will give it to you for free. A few will deliver for a fee. If you pick it up you will need a truck and some strong backs with shovels unless the farmer can load it for you using his tractor bucket.