Completely Updated 9/25/2016: Nobody wants rats in their compost. There are a few ways to get them to scram, and a few other ways to keep them from ever getting in, with varying degrees of cost and difficulty.
Let’s start with the easiest and least expensive.
First of all, take care in what you’re composting, and make sure you’re not adding anything rats especially like to your compost. No animal products
other than eggshells, no bread, no rice. No eggshells, and many people report that potatoes are a favorite rat food. Used coffee grounds are unlikely to repel rats, but rats don’t want to eat them, and they get the compost cooking quickly.
Evicting rats: Chili pepper flakes
If you’ve got rats or other critters visiting your compost, adding hefty doses of chili pepper flakes, also available in bulk, will usually get them moving elsewhere. The flakes are hot on their fingers and mouths, but soon decompose and won’t be hot by the time you’re using it.
This is obviously less expensive and easier than any other option, but understandably, some people want to make sure rats won’t ever get a chance to visit.
Evicting rats: Disturbance
Rats don’t want to live in places that are frequently disturbed, so disturb the compost pile. Turn it, even if it is only with an outstretched arm and a long pitchfork turning the top, disturb it. As you walk past your bin, kick it – repeatedly.
Basically, be a crappy, annoying, disturbing neighbor.
Evicting rats: Destroy the neighborhood
If the “neighborhood” immediately adjacent your compost includes lumber, tall brush, tree cuttings, etc., then get rid of them. Rats appreciate the safety and privacy of these places, so get rid of them.
Evicting rats: Stop feeding the birds, the cat, the dog…
For goodness sake, if you’ve got an unwanted wild animal taking food out of your neat, tidy and contained compost bin, don’t you think they’ll also be attracted to the bowl of food you’re leaving out for Kitty? That they’ll want the seeds spilled by the birds?
Get rid of them! Plant some native flowers for the birds and they’ll be fine. Feed Kitty and Rover indoors only.
Evicting rats: Add coffee
In addition to carefully controlling what you add to your compost (as above, no animal products, including egg shells, no grains, and possibly no potato skins), you can get material cooking quickly with hefty doses of used coffee grounds. Free from Starbucks and many local coffee shops, they’re unappealing to rats and due to their high nitrogen content, they’ll cook down your other items (eg, leaves, vines, yard waste, etc.) quickly.
Improve your existing unit: Hardware cloth
If you’ve taken the steps above but still have or simply want to avoid rats in the future, consider buying some hardware cloth. People often mistakenly refer to this as “chicken wire with smaller, square holes.”
Lay the cloth under your compost bin, making sure you reach slightly beyond the edges. Make sure the bin sits snugly on the hardware cloth to prevent any gaps. You can also wrap the outside of many bins easily, especially the round New Age Composter. You can simply wrap around the compost unit, cutting and tying the ends together with twist-ties.
Easiest and least expensive new composter: Metal trash can
All hardware stores have them in different sizes and different price ranges, but looking at prices today (July, 2016), they’re mostly around $30 for a 31 gallon metal trash can and a few bucks more for a bungee cord.
I intend to use a smaller, $20, 20 gallon trash can, to pre-compost all food scraps. By pre-composting, I’m making the food unappealing to rats and other critters. Using a smaller barrel allows me to easily lift the container and dump it into the other compost bins I already own.
All non-food material can and should still go in your regular compost bin. Having both bins allows you to toss all your spent tomato vines, used coffee grounds, leaves and similar non-edible items in the big compost bin to start cooking, and add this material as appropriate.
Get your trash can home and drill dozens of holes at least 1/4″ diameter but no larger than 1/2″ all over the place, including the bottom.
Rats generally cannot fit through holes 1/2″ in diameter, but mice may. I leave it to you to decide whether you care about mice getting in, and which size holes to make.
Whatever size hole you choose, make sure you’re using drill bits designed to go through metal rather than wood!
You can either place the can on top of the soil, raise it up on blocks, or dig a hole in the ground to slip the can in. If you plan to rest the can on the soil, you might want to invest in some large landscape spikes. Set three or more spikes through holes in the bottom of the trash can for stability, and so marauding raccoons can’t tip it over, or find another way to stabilize it. (Note: I didn’t do this and nobody has knocked the can over, but raccoons certainly CAN do that.)
Use a bungee cord, plastic hook preferably, running from one handle, through the lid handle, and attached on the other side. Why is a plastic hook preferred? Because the metal hooks can hurt you if you’re not being careful.
You can do all of your composting here in the can or you can do your initial composting in the metal can, and once decomposed enough that rats won’t want it, move it to another unit like the New Age Composter that holds more material, to finish it off.
Probably the biggest down side to a metal trash can unit is the quantity of material it can hold, but realistically, a typical family, especially in an urban setting where rats are more likely a concern, will take at least four or more months to fill a 30+ gallon trash can.
Another inexpensive option: Vermicomposting
Similar to how I’ll be using the metal trash can above, vermicomposting allows you to either pre-compost material or let it do the entire job. This is done in the house and can be used year-round. (See Winter Composting Do’s, Dont’s and what if it doesn’t, #4 for more about vermicomposting.)
More expensive: Tumbling composter
I really dislike tumbling compost units. I find they hold little material, they’re usually difficult to turn, difficult to keep at an appropriate moisture level, difficult to empty and really, really expensive.
That said, they assemble in minutes and are very difficult for an animal to penetrate. Generally I think they’re awful though. Seriously. They’re pretty annoying and difficult to use.
More expensive and more work but hold lots of material: Compost Knox
You can custom build very attractive three-bin (or more or less) units made out of pressure treated or recovered plastic timbers, line the bottom and walls with hardware mesh, place 4″ thick concrete blocks on the bottom and a shield of sorts on top.
But unless you’ve got a big garden, why would you?
One model like this I’ve seen and can recommend is the Compost Knox. If you’ve got a big garden, or if you want to do a lot of composting without emptying a metal trash can, this may be what you’re looking for.
Most expensive: Bokashi
Bokashi composting uses material to ferment food indoors, making it unpalatable to rats and other critters, and can then be added to your compost bin outdoors. It’s expensive and time-consuming and I generally think of this as the most expensive and least convenient option.
Other options, including free
The other options are limited only by your imagination. You can:
- Pay a company to pick up on a regular basis for you,
- Make a unit entirely out of hardware cloth, or,
- Bring food scraps weekly to the Farmer’s Market.
If you’ve got a favorite way of dealing with the problem, I hope you’ll let us know in the comments below or by email.