Buzz
Gardeners and farmers have long depended on one of nature's most plentiful materials for fertilizer: animal dung. It’s typically cost-free and simple to acquire, whether from your own livestock or someone else's.
Using animal waste as fertilizer has traditionally been seen as safe—most manure is composted before use, undergoing a heat treatment process that minimizes contamination risks.
However, current health concerns and warnings highlight the need for caution when using manure at home. For instance, two deaths have been linked to harvesting bat guano. With ongoing H5N1 avian flu outbreaks, it’s crucial to be extra careful when fertilizing your plants.
Manure is typically an excellent source of cost-free fertilizer
Though the concept of collecting animal waste might seem odd to those unfamiliar with gardening, manure is an ideal fertilizer when properly treated. It’s packed with nutrients derived from the animals' diet, and if it’s from your own animals, you know exactly what they’ve consumed. Additionally, manure is entirely organic and often available at no cost.
Certain types of manure are classified as “cold,” meaning they can be applied directly without harming plants (such as waste from rabbits, ducks, and goats). On the other hand, manure from chickens, cows, and horses is considered “hot” and can damage plants if not properly treated. By stacking the manure, maintaining a balanced carbon-to-nitrogen ratio, and allowing the sun and composting process to heat it, you can create nutrient-rich compost. Many commercial fertilizers also highlight their inclusion of animal manure.
Animal manure can harbor diseases
The issue is that manure can also contain diseases, fungi, and other harmful pathogens. While composting can eliminate some of these, it doesn’t remove all of them. Although the risk of these pathogens transferring to your produce is minimal, the danger to those handling the manure is significant. If manure is applied directly to plants, fruits, or vegetables and not thoroughly washed off, it can remain on the surface, posing a risk.
Even certain commercial fertilizers might pose health risks
Recently, two men died in separate incidents after inhaling spores from bat guano, which is often considered highly beneficial for cannabis cultivation. In one case, the individual manually collected guano from wild bats, while in the other, the person used commercially purchased guano on cannabis plants they grew and consumed.
Most commercially sold fertilizers are regulated and deemed safe. However, in the U.S., fertilizer regulations are managed at the state level, leading to varying enforcement and standards depending on the origin or sale location. In the study linked above, scientists Dr. Sudnik and Dr. Ted Louie highlight that commercially available bat guano fertilizers do not warn about the risk of histoplasmosis, the disease that caused both deaths, and emphasize the need for caution when using such products.
Wearing masks or respirators can generally safeguard gardeners from exposure when handling animal waste products.
Avian flu (H5N1) remains a concern in chicken manure
Chicken and other backyard fowl manure, far more common than bat guano, is a widely used fertilizer. However, this poses a concern as the world faces a highly pathogenic strain of avian flu (H5N1). The virus has been detected in cows, pigs, domestic and large cats, and has even infected humans. When H5N1 is identified in farm animals, they must be culled to prevent further spread.
Bird manure is the primary transmission route for avian flu. Infected birds leave droppings that other animals consume, leading to infection and further spread. While large farms are the main concern, backyard flocks are also at risk. Handling bird manure can be hazardous for humans, as this highly pathogenic virus can persist in manure even after composting if the temperature isn’t high enough for a sufficient duration.
Handling manure without protection is risky—so it might be best to avoid it entirely
“Given the current situation, I wouldn’t handle animal manure without proper protective gear,” said Dan Teich, DVM, a veterinarian and owner of District Veterinary in Washington, D.C. “That means an N95 mask or respirator, goggles, gloves, and thorough cleaning afterward.”
Alternatively, consider avoiding manure altogether (pun not intended). It’s wise to refrain from using backyard or farm manure in your garden during these ongoing threats. While commercial fertilizers are generally safe, always check labels for usage instructions and opt for products that have undergone treatment and are clearly labeled as safe. Consult your local garden center for recommendations on safe and vetted fertilizers.
