Managing Rats in City Gardens
Many gardeners have had at least one encounter with rats; the typical urban gardener has probably had many. There is only one species of rat in New York City—the Norway rat (Rattus norvegicus). The Norway rat is a commensal rodent, meaning it lives in close association (literally, “shares the table”) with humans. Urban gardens are particularly hospitable to rats because they provide food, water, and safety.
Rats will burrow into any available earthen space within close proximity to food but prefer fresh, fertile soil to make their nests—a garden is prime real estate to them. A rat burrow can be anywhere from one to six feet deep and will have an entrance, an exit, and maybe even an escape hole. A typical burrow will house a family of approximately eight rats. By counting the burrow holes gardeners can estimate the number of rats living in their garden.
Gardeners are usually left up to their own devices when it comes to pest control. Some people want to maintain a pesticide-free environment; others are desperate to get a bad situation under control and will try any remedy. Rats can usually be managed effectively without relying on toxic pesticides. In fact, a good rat management program focuses primarily on prevention.
Learn What Rats Need and Eliminate It
Recognizing how to make your space less hospitable can help you to devise a rodent-reducing plan. Rats must eat one to two ounces of food a day and have daily access to water. Rats will eat everything that humans eat and many things that we would never eat. They are not vegetarian; like most mammals, rats (especially reproducing females) need animal protein, fat, and carbohydrates in their diet.
Rats will eat the vegetables and fruits in a garden, but if that is truly their only food source, they will eventually move on to a site that meets their animal protein and fat needs. A compost pile with only garden scraps will not sustain a rat colony. But if table scraps including meats, grains, oils, or other fats are added into the compost pile, it will become highly attractive to them. And the warmth generated by decomposing waste creates a hospitable rat environment in cold weather. Compost areas must be monitored carefully, and if possible, kept in hard plastic or metal containers with tight-fitting lids.
Bags of trash placed near a garden offer an all-you-can-eat buffet to a colony of rats. Like compost, trash should be kept only in sturdy cans with tight-fitting lids. Gardeners should always clean up after picnics and make sure food waste is removed at night.
Food intended for pigeons, cats, dogs, chickens, or rabbits placed in or near a garden may also end up feeding rats. Animal waste such as dog feces can also provide nourishment. Some gardeners feed feral cats in the belief that they will scare away rats. The reality is that most cats are quickly overwhelmed. A healthy breeding female rat can have litters of up to 12 pups several times a year, while the average cat may only take down a rat once every couple of days. In areas where lots of rats are present, it’s best to avoid feeding other animals.
For shelter, rats seek out areas where they feel protected from predators. Dense plantings, tall weeds, and piles of lumber, rocks, or other kinds of clutter provide safe harbor to a rat. Ivy and bushes close to the ground and around buildings are particularly attractive. Rats have very poor eyesight and use their whiskers (or vibrissae) to navigate their environment; as a result, they prefer to travel along straight lines and use curbs, walls, and foundations to get around. Gardeners battling a rat infestation can cut back vegetation at least 18 inches from building walls, remove ivy or other vines from sides of buildings and nearby trees, and trim back tree branches that touch or rub against buildings. Deprived of cover, rats will be less confident traversing these exposed zones and may move on to safer places.
A gardener can figure out where rats are traveling by looking along straight lines for the greasy rub marks that rats leave behind. These rub or smudge marks contain pheromones from the rat’s skin and fur that they use to communicate with other rats. Washing the rub marks away with vinegar or biodegradable soap can help interrupt their established pathways to food sources and home. Hardware cloth (half-inch mesh) can be installed along the base of walls or fences to deter burrowing. The cloth should extend 8 to 12 inches underground. Even though rats can burrow deeper than this, many rats are deterred from spending so much energy to create a nest.
A Rat Reduction Plan
- Move compost into rodent-resistant containers with tight-fitting lids.
- Store seed and pet food in rodent-proof containers.
- Remove fallen fruit or nuts.
- Remove all fecal matter (dogs, cats, rodents, birds) and/or food waste every day.
- Eliminate standing water and improve drainage, so water doesn’t pool or settle.
- Remove clutter from storage sheds and garages.
- Cut grass or weeds and trim back plants around buildings and walls.
Monitor for Rats
The early spring prior to planting is the best time to start watching for rats. Gardeners should carefully check garden areas before planting seeds as well as later when vegetables and flowers are actively growing. Look for burrow holes, smudge marks, signs of gnawing, worn pathways, and droppings, all of which indicate an active rat infestation. Check around the garden perimeter a few times each week for any new rat activity and take steps to stop it.
In short, think like a rat. Where do I like to live? What am I eating? What pathways do I travel between my food and nest?
Know When to Call in the Pros
If things get really bad, the best thing to do is hire a pest professional. In New York, they should be certified by the New York State Department of Environmental Conservation (DEC). Tamper-resistant bait stations with EPA-registered rodenticide bait can be installed by a professional and monitored over time. They should be checked and replenished every week or month depending on the severity of the infestation. Make sure you walk the area with your professional and discuss the treatment plan together.
Snap traps work also work very well, but they must be installed in boxes to prevent birds, dogs, cats, and even children from encountering them. They should be checked daily, emptied, and then reset.
Poison dusts to sprinkle or blow into rat burrows are illegal for gardens and must never be used—not even by a certified professional. They are not only poisonous to rats but could also be harmful to other animals and children if ingested.
Finally, beware that some commercially available devices don’t work and are essentially a waste of time and money. These include sonic devices that claim to scare away rats; there’s no scientific proof that they actually work. Nor have mothballs, pepper sprays, peppermint, or other smelly chemicals been proven to deter rats. Cat, dog, or human hair or urine sprinkled in a garden also appears to have no impact on rats. Beware of anyone claiming they have a secret weapon or chemical that will get rid of rats. There is none.