How to Keep Rats at Bay

Q: Rats are a huge problem in city gardens, chewing through fences and basement doors, boring, burrowing. The poisons, traps, organics and predator urine don’t stop them for long. Our block is invaded! The rats are very good at gnawing through/burrowing around barriers such as Grade 3 steel wool. Do we all have to dig five feet and pour cement?

A: As you’ve experienced, rats have amazing abilities to multiply and get into places they want to be. A female rat can mature enough to start reproducing after only three or four months, and can have eight or more babies every month. Adding to the problem is the fact that rats are rodents, which means their teeth grow constantly – five inches a year. They need to chew through wood and other materials just to keep their teeth trimmed. And of course they often gnaw or dig to get to food, which can be almost anything: the food we eat, even if it’s rotting, as well as pet waste and other things we’d never touch. Because rats have long, flexible bodies made for burrowing, adults can squeeze through holes as narrow as the diameter of a quarter. Rats typically burrow down about 18 inches to nest (if they can’t find an indoor home), but they are capable of digging down much deeper if a foundation is in the way and they think food is on the other side.

Obviously, predator urine probably isn’t going to stop them. But your mention of steel wool and concrete is on the right track. To keep rats out of buildings, it does work to seal all holes and to fortify places where they gnaw. If you don’t have the time or the ability to seal all holes in exterior floors, walls and foundations, hire a pest-control company to do this for you. Removing easily accessible food also goes a long way. The castoffs from outdoor bird feeders and open garbage cans or compost piles, for example, are a huge draw for rats.

However, when it comes to keeping rats out of gardens or dealing with a neighborhood-wide infestation, exclusion alone probably isn’t going to work. You can keep them from digging into specific garden beds by placing sturdy, quarter-inch wire mesh under mulch or soil where rats have been digging. But there is no way to wall them out from a whole yard or neighborhood.

In Washington, inspectors with the Health Department’s Rodent Control division are certified in rodent control and arrive with rodenticides, baits and tracking powder. Your local inspectors can also look around and recommend things you might not have thought of that can make a difference. Among the strategies on the department’s website for keeping down rat populations outdoors:

– Eliminate clutter, especially under porches or other sheltered places.

– Store garbage in metal or heavy plastic containers with tightfitting lids. The best strategy is to store food waste in a plastic bag in the refrigerator until the morning of garbage pickup. Grease, with its high calorie count, should go in a container with a tightfitting lid, wiped free of grease on the outside. Wait until shortly before pickup to move your garbage can to the collection point. Doing that days in advance increases the likelihood that lids will come loose or that rats will gnaw through your garbage can. If your neighborhood has street litter bins, keeping them free of food debris also helps.

– Make your landscaping less hospitable to rats. Remove weeds and debris and replace plants known to provide cover, including English ivy, periwinkle, pachysandra and hosta.

Rats also need water to survive. You can’t do anything to make a nearby stream less enticing, but if your home is away from a natural water source, you can fix dripping faucets and remove or tip over any containers that hold rainwater.