Adding manure to the garden provides a wealth of plant nutrients, right?
Yes, it does!
It can also make you very, very sick.
Improper management of manure in agriculture is what leads to those massive recalls of grocery store lettuce and salad mixes. Yes, it can kill you. But don’t panic, there are steps you can take to make it safe.
Chicken bedding, rabbit droppings, horse manure, and cow patties are filled with valuable plant nutrients. Rather than allowing those resources to go to waste [Sorry, I couldn’t resist], you can put them to good use in the garden by following some simple safety precautions.
Benefits of manure
Plants don’t care what you feed them. To them, an element is an element, wherever it came from. Instead of buying fertilizer, you can grow great soil by adding organic material such as manure. Animal manure provides far more than chemical nutrients. It is the slow-release vitamin plants need to grow and thrive - 700 million years of evolution can’t be wrong!
In addition to nutrients, manure contains undigested feed and bacteria that improve soil structure, increase water and nutrient retention and water holding capacity, reduce erosion, and supports important soil microorganisms. Incorporating manure into your garden soil improves its tilth, making it far easier to work.
Nutrient content of manure
Sadly, animal manure does not contain as much nitrogen as you might have hoped. Nitrogen occurs in two forms in manure: organic and inorganic. Organic nitrogen (N) is a slow release nutrient. Inorganic nitrogen occurs as ammonium (NH4+) and nitrate (NO3–) and is immediately available to plants. But you need to act quickly, when it comes to nitrogen.
Nitrogen is a highly volatile element. Left to sit on the surface, nearly 100% of the nitrogen is lost to the atmosphere in a process called volatilization. If manure is incorporated into the soil right away, only 20% is lost. If you are a fan of no-dig gardening, composting will be your only option.
Manure contains high levels of potassium and phosphorus, which your soil may or may not need. I’ve said it many times: get your soil tested by a reputable lab before adding anything. to avoid creating toxicities (and wasting money).
Manure also contains many important micronutrients. Varying levels of calcium, copper, magnesium, manganese, sulfur, and zinc may also be present in animal manure. But not all manures are created equally. Even within a species, nutrient values can vary. Still, there are ranges of nutrients found in most manures and beddings that make them a valuable asset to the home gardener.
Did you know that broiler chickens produce a different manure than roaster chickens? I didn’t either, but you can look at a chart from the Clemson University Extension if you want to learn more.
Raw manure should never be applied to the soil while plants are growing. If it is, be sure that the manure does not touch the plants. After manure is applied, plants that come into contact with the soil (lettuces, melons, squash) should not be harvested for 120 days. Crops that do not touch the soil (tomatoes, corn, pole beans) should not be harvested for 90 days. But you can’t wait that long, you say? What about composted manure? At what point does it become safe to use?
Simply allowing manure to sit in a pile until it looks done is not adequate to protect your family’s health against disease. Many pathogens can survive for years in a pile of poo.
Research has shown that manure must be composted for at least 45 days, 15 of which must be at temperatures between 131°F and 170°F, and turned at least 5 times to be safe to use. Assuming it hasn’t been recontaminated by air-dropped bird poop or other pathogens.
How certain are you that those temperatures have been reached? Seriously. If you are using manure in your garden, you need to be out there with a thermometer and a pencil, documenting those temperatures. You can get a soil/compost thermometer for around $10. Compared to trip to the emergency room, it’s worth it.
As many of you already know, I raise chickens for eggs and compost. Poultry manure has a high nitrogen content and, mixed with straw bedding, makes for an excellent soil amendment. I only feed my hens organic laying pellets, organic treats, and mostly organic kitchen waste, so I feel safe using it after it has been properly composted.
Before you accept a truck load of cow or horse manure from the local farm or stable, keep in mind that you have no control over medications being used on those animals, or on any pesticides, herbicides, or other chemicals that were used on their feed and which can pass through their digestive systems. Signs of toxic manure include poor germination rates, seedling death, distorted leaves and fruit, and smaller harvests. Also, horse and cow manure tends to be high in salt, which is fine once in a while, but it can build up to toxic levels if used too frequently.
Many people worry that using manure will make their garden smell bad. Properly aged manure smells more like rich earth. Mushroom compost, as my Gilroy neighbors know, has a much more pungent aroma.
Now you know.
You can grow a surprising amount of food in your own yard. Ask me how!