Collecting compost is a common practice in any environmentally-conscious home. Not only is creating this natural fertilizer an easy way to reduce household waste, but the organic matter also adds valuable nutrients to the soil and has even been shown to suppress harmful pathogens that can thrive underground. However, a new study published in Nature Microbiology reveals that a drug-resistant fungus may grow in compost and infect humans that inhale its spores. 

The culprit, Aspergillus fumigatus, is a common fungal pathogen that has infected people all over the world, including over 2 million in the European Union alone. But the drugs typically used to treat A. fumigatus have become less effective in recent years, and this drug resistance puts at-risk populations like leukemia patients in even greater danger.

Similar to how some bacteria can become drug-resistant after encountering antibiotics, antifungal resistance may result from exposure to agricultural fungicides, the study says.

With that in mind, it’s important for eco-friendly gardeners to keep themselves safe.

Know what’s compostable and what’s not

One easy way to maintain a clean compost bin is by adhering to a strict list of compostable goods. The Environmental Protection Agency recommends adding equal amounts of “greens” and “browns” to compost, and the proper amount of water. Only composting the recommended items will help keep your compost bin efficient and clean.

The volume of your container can also help move microbes along. Cornell’s Waste Management Institute says containers between 3 and 5 feet cubed (27 to 135 cubic feet) will create the fastest compost. Smaller containers struggle to hold in the heat generated during composting, and larger containers make it difficult for air to reach the internal microbes. During dry periods, adding water will also help the decomposition process by sustaining microbes.

[Related: How to start composting at home]

To determine if your compost is breaking down quickly, just take its temperature. Microorganisms produce heat when they decompose organic material, and high heat is associated with fast decomposition.

High temperatures also help keep compost safe. The EPA says that to significantly reduce pathogen numbers, compost should be kept at 104 degrees Fahrenheit for at least five days, and over 131 degrees for at least four hours within that same timeframe. This time helps destroy fly larvae, weed seeds, and some pathogens sensitive to temperature. However, most microorganisms cannot survive in temperatures above 140 degrees, so if your compost starts to approach that benchmark, you should mix it up to cool it down.

After this stage of rapid decomposition and high temperatures, which may take weeks or months, decomposition will slow and your compost’s temperature will drop. The final stages of composting help stabilize the stuff so you can use it in your garden.

How to keep mold out of your compost bin

Unfortunately, you simply cannot clear all microorganisms and fungi out of your compost bin. Compost needs microorganisms and fungi to turn waste into fertile compost. In addition, A. fumigatus is so common that people inhale its spores repeatedly throughout the day. Most people can breathe in the spores with no reaction. But when it infects immunocompromised patients, they face severe health risks, including death. With so many spores around, Cornell recommends several key safety measures beyond proper composting materials and temperature control.