Keeping Pests Out of Your Compost

By John Wallace, SIFT Farm Manager

Depending on where you live, a pile of compost may bring in some unwanted guests. Sometimes it’s not necessarily the food scraps they are after, but the worms and bugs that thrive in this micro-environment. Rodents, such as raccoons, skunks, mice, and voles are among the biggest culprits. Deer, fox, coyotes, and often domestic animals can also be disruptive. Though the compost might offer them an easy snack, they likely will not harm the compost. The main worry is luring in animals in close proximity with your farm or garden.

The SIFT farm compost pile.
The SIFT farm compost pile.
Photo: NCAT

The first step you can take to protect your crop is to separate your compost site from your production area. Selecting your site is important not only for keeping pests away but for limiting any cross-contamination from uncooked compost or potential soil-borne diseases. If your only option to place your compost pile near your production area, it is important to exclude or limit potentially harmful ingredients such as raw manure, diseased vegetation, and animal products. Remember, if you have enacted a food safety plan, you will have to keep raw compost separate from designated foot traffic areas to minimize any risk of contamination.

Animals are brought in by the smells that compost often puts off; however, if done correctly, there should not be much of a smell. Though animal products such as dairy and meat can effectively be composted, it is not recommended because they can bring in harmful microbes and rotten smells. Also, leftovers that have oils and seasonings can increase the likelihood of enticing pests. Keep these products out of your pile.

If you get a strong stench, your compost has likely gone anaerobic. This is because the macrobiotic processes have begun to expel methane. Not only is this bad for attracting pests, but it is also a very strong greenhouse gas that is bad for our atmosphere. There are a few reasons why compost can go anaerobic. One is that the compost has not been turned enough and layers of leaves, straw, or paper have encapsulated the inside and will not allow oxygen to infiltrate. Over-watering without turning can also cause these layers to collapse and close off air pockets.

Another reason for compost to go anaerobic is if your carbon-to-nitrogen (C:N) ratio is not balanced correctly. In the compost world, we refer to the materials as browns and greens. Browns are high in carbon and greens are high in nitrogen. Typically, materials that are brown, such as cardboard, leaves, straw, and brush are high in carbon. Alternatively, grass and food scraps are high in nitrogen. Other “greens” that may not necessarily have that color are manure and coffee grounds. The ideal C:N ratio is about 30:1. If nitrogen levels are too high, the compost pile will heat up too quickly and will kill off aerobic bacteria. You can tell if your compost pile has done this if you find a layer inside that has a silvery white discoloration. Measure the temperatures of you compost and turn it before it exceeds 150 degrees F. Though the composting process can begin at temperatures as low as 105 degrees F, It is necessary to reach 130 degrees F in order to kill weed seeds.

If these steps still aren’t keeping out pests, the last resort is to deter or build physical barriers. Fencing, chicken wire, or pallets can all be used to fortify compost bays to keep animals out. Whether you protect just the compost pile itself, or the entire perimeter, will depend on the location of your site and what you are trying to keep out. Another tip is to tarp the pile to prevent wafting smells. This will also help keep moisture in your pile and avoid oversaturation from heavy rains. Deer tend to disregard any attempt at blocking them out with fencing or other approaches. 3D fencing has shown positive results and involves stringing multiple wires at different depths and heights to make the deer think he would get tangled if it were to jump the fence.

On the SIFT farm, voles are our main culprit. Even though voles aren’t necessarily disrupting the composting process, they tend to breed and spread elsewhere. They often feed on the roots, stems, and fruiting bodies of plants in their proximity. They can also destroy the soil’s properties by burrowing tunnels that disrupt the flow of water through the ground. Simply flooding the outside of the compost area can help push them out; however, this is not recommended for the production area because over-saturating the soil will sink the air pockets and cause poor drainage in the future. As well, turning your compost often will help destruct their tunnels. If problems persist, consider castor oil granules. . The voles do not like the smell and will not attempt to enter an area where it is present. We’ve used these effectively as an organic tool to deter voles on the SIFT farm. You can purchase castor oil granules at any home and garden supply store.

Learn more about composting in the ATTRA publication Composting - The Basics.

Posted on: September 25th, 2018