Mold in Compost Piles

Lauren Thomason

Organic matter takes years to decompose fully when left untouched. Compost piles speed the decomposition process significantly, and they allow gardeners to turn yard waste and tables scraps into usable garden materials and soil additives. Mold is a natural part of composting, and it actually helps to speed the decomposition process inside compost piles.


You can turn unwanted garden waste into nutrient-rich compost.

Compost is somewhat acidic, and so it makes sense that fungus and mold grow in compost piles. If a compost pile has no mold growth, the compost materials may not be balanced correctly for optimal decomposition. The more nutrient-rich the compost matter is, the more likely you'll see mold or fungus.


Although most garden waste and table scraps can be placed in a compost pile, the pile needs a proper balance of "brown" and "green" materials to be productive and decompose matter quickly. Typically, a compost pile requires a ratio of two parts brown matter, such as dry leaves, to one part green matter, such as grass clippings. Table scraps, including potato or carrot peelings and coffee grounds, work well in compost heaps because they add extra nutrients to the compost mix. A well-maintained and well-balanced compost pile's aroma is the same as the aroma of a forest floor. Never place fatty or animal products into a compost heap. They tend to produce a foul odor and attract garden pests.

Shredded Leaves vs. Non-Shredded Leaves

Leaves produce mold quicker when they are shredded. Non-shredded leaves tend to stick together and decompose slower -- up to two or three years instead of the typical six months to one year.


Mold in your compost pile is not anything to worry about, unless someone in your family has a severe allergy to mold. Turning the compost bedding stops the process of hairy mold growth. Add water to the pile it the bedding looks too dry, keeping compost at about the moisture level of a wrung-out sponge.


Vermicomposting in containers uses worms to help make the composting process even faster. Mold is also natural in a vermicomposting bin, but too much mold may turn the bin sour. Adding some slow-releasing, pH-balancing materials, such as crushed eggshells, keeps the matter inside the bin more equalized. Gently turn the materials by hand to prevent hurting the worms inside the bin.