Don’t put fibrous vegetables, starchy foods, grease, or anything hard like bones into a garbage disposal. Those four categories cover the vast majority of jams and clogs. The rest of this article explains why each one is a problem and what the conflicting advice you’ve read online actually gets wrong.
Fibrous Foods: The Jams You Feel Immediately
Celery, artichokes, corn husks, asparagus, and chard are the worst offenders. The long stringy fibers don’t cut. They wrap around the impellers and motor shaft. The disposal usually keeps running but the impellers slow down or stop, and you get a grinding sound followed by a breaker trip or the thermal overload shutting the unit off. You press the reset button on the bottom, it hums, you press reset again. That cycle is almost always fibrous material wrapped around the shaft.
Onion skins are in the same family. They’re thin so people assume they’re fine. They’re not. The papery outer layer can pass through the impellers and lodge in the drain pipe just past the unit, where it forms a net that catches everything else.
Starchy Foods: The Slow Clogs That Sneak Up
Potato peels are the classic culprit. A few go in, they seem to grind fine, and you don’t think about it. But potato starch turns into a thick paste when it gets wet and sits in the drain. Over days, it coats the inside of the pipe. The same thing happens with pasta, rice, and oatmeal. They expand with water and create a dense, sticky layer.
The reason this kind of clog is frustrating is that it builds gradually. You won’t notice a problem until the drain is already significantly narrowed. By then the blockage may be 10 or 15 feet down the line, not right under the sink, which makes clearing it harder.
Grease, Fats, and Oils
Pour liquid grease down the disposal and it travels fine as long as it’s warm. The problem comes further down the drain where the pipe is cooler. It solidifies there. Do this enough times and you build up a layer that traps food particles from every meal after. This kind of buildup is what professional plumbers call “FOG” (fats, oils, grease) and it’s the most common cause of recurring slow drains in kitchens.
Peanut butter, cooking oil, and even heavy butter all behave the same way. The disposal doesn’t help here. It just liquefies things that will re-solidify once they cool.
Hard Items: Bones, Fruit Pits, and Seeds
Small chicken bones can jam or damage the impellers over time. Large bones, peach pits, cherry pits, and avocado pits can crack the grind ring or seize the impellers outright. If you hear a loud grinding clank and the unit stops, something hard is usually jammed between the impeller and the grinding ring.
The disposal can sometimes self-clear a small hard object if you use the hex-key slot on the bottom of the unit to manually rotate the impeller plate. But if it seized on something large, you’re looking at a service call.
The Eggshell and Coffee Grounds Debate
You’ll find conflicting advice online about both, but most of it resolves clearly once you understand how the unit works.
Eggshells: Some sources say the membrane inside the shell wraps around the impeller shaft just like fibrous vegetables. Others say the shells help sharpen the blades. The sharpening claim is a myth because disposals don’t have blades. They use blunt impeller lugs that fling food against a stationary grind ring. The real concern is the thin inner membrane, which can wrap around the impeller shaft and also behave like onion skin in the pipe. A few eggshells won’t ruin a disposal, but they add no benefit.
Coffee grounds: They pass through the disposal without issue. The problem is that grounds are dense and compact. If there’s any grease or starch buildup already in the pipe, grounds accumulate on top of it quickly. They’re not the cause of most clogs, but they accelerate existing ones. If your pipes are clean, occasional grounds are probably fine. If you’re already having slow-drain issues, stop putting them in.
What’s Actually Safe
Running cold water while the disposal is on and for 20-30 seconds after you stop it. Small pieces of soft food. Citrus peels in small amounts (they don’t clean the disposal the way people claim, but they don’t cause problems either). Ice cubes occasionally, which can help dislodge mild buildup on the impellers.
The cold water point matters: hot water melts grease as it passes through the disposal but it re-solidifies downstream. Cold water keeps the grease solid so the impellers can actually shred it before it enters the drain.
When to Call a Licensed Plumber
DIY-safe territory: pressing the reset button on the bottom of the unit, using the hex-key slot to manually rotate a seized impeller, checking that the unit is plugged in, running water to see if the drain is slow versus completely blocked.
Not DIY territory: anything involving the P-trap or the drain line beyond it, any situation where water is backing up into the sink, a humming unit that won’t turn even after you’ve manually freed the impeller, or any leak at the connection point between the disposal and the drain.
For anything beyond the reset-and-rotate, you need a licensed plumber. In California, you can verify a plumber’s license before they arrive at cslb.ca.gov. It takes 30 seconds and it’s worth doing. Garbage disposal work isn’t glamorous but an incorrectly repaired P-trap or drain connection can leak inside a cabinet for months before you notice, which turns a modest repair into a much larger one.
If the unit itself is dead (no hum, no response after reset), it may need replacement. That’s also a licensed plumber job, not because it’s technically difficult, but because the electrical connections and the drain plumbing both need to be done correctly.