Finding rats or evidence of the rodents in and around your compost bin can be unsettling. The black rat and brown rats commonly found around homes in North America can be 6 to 12 inches long, not counting the long hairless tail, and spotting one around your home is guaranteed to create a feeling of revulsion. Few people will mistake a rat for the much less repulsive house mouse, even though there is a superficial similarity in appearance.
These persistent rodents have been known to chew through wood, wire, plastic, and just about anything else that gets in their way, so even commercial compost bins can be vulnerable. Rats multiply at alarming rates; one pair can multiply to more than one thousand baby rats in a year. These rodents are also known to carry diseases. Whether you live in the city, suburbs, or country, chances are good you may end up dealing with rats at some point, though those in warmer climates and urban environments are more likely to face chronic rat problems.
5 Ways to Keep Rats Out of Your Compost
In general, rats are looking for two basic things: food and shelter. When a compost pile meets both needs, a rat problem becomes a real likelihood. Fortunately, there are five simple ways to prevent rats from getting into your compost pile and to get rid of them when they have already arrived.
Bury Food Scraps in the Pile
Usually, rats are drawn to compost piles because they are easy sources of food. In general, you should never add meat or dairy products to a compost pile because those items are a sure draw for rodents (there is an exception to this if you use Bokashi to ferment kitchen waste). If they're hungry enough, though, even your potato peels might start to look pretty tempting to rats. Whenever you add food scraps to the compost bin, either dig in a little and deposit your food waste deep inside the pile before covering it over, or add a couple of inches of grass clippings or leaves on top of any food scraps. Out of sight (and smell) may keep rats from finding your compost pile.
Don't Compost Any Food Waste
If rats are a real problem, you may want to forego adding food waste to your compost pile altogether. Don't waste those valuable scraps, though. Set up an indoor vermicomposting bin for food waste, or bury it directly in the garden in compost trenches.
If you use Bokashi to deal with your kitchen waste, you are familiar with the odor fermented kitchen waste has. It turns out that even the hungriest rat steers clear of Bokashi-fermented food waste. Throw your food waste into the Bokashi bucket, layer it with the Bokashi bran, let it sit for two weeks, and then add the contents to your compost pile. It breaks down quickly, and rats won't even consider touching the stuff.
Keep Compost Contents Moist
One of the two things rats are looking for when they invade your compost is shelter. A dried-out compost pile is inefficient in terms of breaking down organic material into compost, and it's a haven for rats. A dry compost heap provides a perfect warm, insulated place to sleep with tasty morsels located within easy reach. If you make sure your compost pile is always moist throughout—not wet, which results in anaerobic conditions and unpleasant odors—it won't be a place rats want to make their own. By turning the pile regularly and giving it a bit of water during dry spells, you can make it much less hospitable to rodents.
Plant Mint Nearby
This is one of those tips that seems to work for some people and not for others, but it's worth a try. Mice and rats are reputed to hate the scent of mint, so if you plant a few mint plants close to your compost pile, it may be enough to deter the pests. However, if you have a very large or very hungry rat population in your area, it's unlikely that a little mint will fully deter them. Peppermint seems to work most effectively.
What Causes Rats in a Compost Pile?
Rats are drawn to a compost pile when it provides shelter and food. Omnivorous scavengers, they will eat almost any decaying food materials, including animal flesh and bones, rotting fruit, and vegetable and fruit peelings. No compost heap is fully immune to rats, but compost with a high percentage of table scraps is much more likely to experience a problem. If you add to this a good ratio of dried materials, such as sticks, straw, or dried leaves, the pile is likely to experience a rat problem if it is not turned regularly. It's easy for rats to hollow out dry nesting sites in an undistubed pile that has plenty of nesting materials.
How to Prevent Rats
In addition to the tips outlined above, turning and inspecting the compost heap regularly is likely to prevent rats from building nests inside the pile. Turning the pile regularly will destroy any nests being formed, and it thoroughly blends the contents so table scraps aren't presented in a buffet-style manner for the rats' convenience.
It's also a good idea to keep your compost bin isolated in the yard, well away from the house or garage. This will prevent rats and other rodents that do try to infest the compost from finding easy access into your home. As weather turns cold, various rodents are often looking for a way into your house and a place to spend the winter in comfort.
Rats vs. Mice
Many rodents are attracted to compost heaps, and the most likely other tenant is the ordinary house mouse (Mus musculus), which at first glance looks a lot like a small rat. Mice, however, are considerably smaller rodents, averaging about 3 inches long, and they have tails covered with fine hair, unlike the completely hairless tails of the much larger rat. But mice are also disease carriers, and they are also likely to find cracks and crevices through which to invade your home when the weather begins to turn cold. The same preventive measures used for rats will keep mice from using your compost heap.
Do Rats Carry Diseases?
Rats deserve their reputations as filthy pests, as they are known to carry a number of serious disease-causing pathogens, including hantavirus, leptospirosis, lymphocytic choriomeningitis, yersinia pestis (plague), and Streptobacillus moniliformis, which causes rat-bite fever. There are few known cases, if any, of rats carrying rabies, however.
Will Rats Leave on Their Own?
If the compost conditions that are favorable to rats—shelter and food—are eliminated, the rodents will soon move on to other locations where conditions are more to their liking. Unlike other pests, rats move around readily and will not linger when shelter and food are not available.
Can I Use Poison?
While there are a number of commercial rodenticides available that will kill rats, it is a bad idea to use these in outdoor settings, as wild animals and pets are likely to find and eat them. Once squirrels or rabbits eat the poison and die, the dogs, cats, foxes, or hawks that eat the carcasses will be poisoned, as well.
Can I Use Traps?
Both live traps and various kill traps can be used to catch rats in and around a compost pile, but these traps are also likely to catch wildlife creatures, such as chipmunks and squirrels. So it takes some technique to make sure that only rats have access to the traps. Unless you also alter the conditions that lure rats in the first place, it's likely that more rats will keep coming, no matter how many you trap.