Vegetable Oil In Compost Bins: Should You Compost Leftover Cooking Oil

Vegetable Oil In Compost Bins: Should You Compost Leftover Cooking Oil

By: Amy Grant

If you don’t have your own compost, chances are good that the city in which you reside has a compost bin service. Composting is big and for good reason, but sometime the rules about what is compostable can be confusing. For instance, can vegetable oil be composted?

Can Vegetable Oil Be Composted?

Think about it, vegetable oil is organic so logically you would assume you could compost leftover cooking oil. This is sort of true. You can compost leftover cooking oil IF it is in very small amounts and IF it is a vegetable oil such as corn oil, olive oil, sunflower oil or rapeseed oil.

Adding too much vegetable oil to compost slows down the composting process. Excess oil forms water resistant barriers around other materials, thereby reducing air flow and displacing water, which is necessary to aerobic composting. The result is a pile that becomes anaerobic and you will know it! The stinky smell of rotten food will repel you but send out a welcoming aroma to every rat, skunk, opossum and raccoon in the neighborhood.

So, when adding vegetable oil to compost, only add small amounts. For example, it’s okay to add the paper towels that soaked up some grease but you don’t want to dump the contents of the Fry Daddy into the compost heap. When composting vegetable oil, make sure your compost is hot, between 120 F. and 150 F. (49 to 66 C.) and stirred around on a regular basis.

If you pay for a composting service in your city, the same rules may apply, that is a few oil soaked paper towels are okay, but be sure to check with your provider first. Any large amounts of vegetable oil in compost bins would, I’m sure, be frowned upon. For one thing, vegetable oil in compost bins would be a mess, smell, and, again, attract vermin, bees and flies.

If you don’t even want to try composting vegetable oil in very small amounts, don’t rinse it down the drain! This can cause a clog and backup. Put it into a sealed plastic or metal container and dispose of it in the trash. If you have a large quantity, you can reuse it or if it’s gone rancid and you must dispose of it, contact your local government or Earth911 to find facilities that will recycle it for you.

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Read more about Compost Ingredients

Can I Compost Fats and Oils?

No, you shouldn’t compost fats and oils.

The benefit of adding waste fats and oils to a compost heap are vastly outweighed by the potential problems. Not only can they attract rodents and other undesirable creatures to your compost heap, they can cause problems for the composting process: the oils can form water-resistant barriers around other material, displace water and reduce air flow in a heap, thus slowing down the composting process.

A tiny smear of butter or grease on a piece of kitchen roll or a carrot won’t be a huge problem for a compost heap but more than that will start to cause problems.

Fats that are solid at room temperature can be reused to make bird feeders for the garden.

Large quantities of used vegetable oil can be recycled – your local council should be able to advise if it is possible in your area.

Waste fats should NOT be poured down the sink – they can clog pipes and sewers, especially those solid at cooler temperatures.

You can actually compost most paper including newspaper, white paper and cardboard, but it is best to shred it and to avoid composting glossy paper or paper that is coated as it may contain toxins.

This is especially the case with greasy cardboard and paper that has been used to hold food, such as pizza boxes and brown paper bags. These cannot be recycled because the grease will contaminate the rest of the paper and it is best to compost these.

The paper that you probably shouldn’t compost includes receipts as these contain BPA, which could contaminate your soil. These are not recyclable either unfortunately.

Some inks used these days are soy-based and therefore natural and non-toxic and will decompose safely, but unless you are sure all the ingredients used to make your paper are natural, we would recommend not composting it.

So, don’t compost types of paper that contain strong dyes, heavy inks or other printing chemicals (unless you’re certain natural alternatives have been used), but do compost all other paper and cardboard, especially if it is greasy.

2. Diseased Plants

Powdery mildew, black spot, damping off, rust, verticillium wilt, mosaic virus, and other plant pathogens can survive the composting process to infect new plants the following season.

Like weeds, diseased plant matter in the compost requires high temperatures to destroy the bacteria, fungi, viruses, and parasites completely.

And even then, all pathogens might not be fully eradicated.

Better to play it safe and keep it out of the heap.

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Does simple logic tell you that cooked vegetables can go into your compost? If so put them there. Why would it not be good to put cooked vegetables in compost? What confused logic did the writter of that article use to justify not putting cooked vegetables in compost?


I think the reason some people recommend agains putting cooked vegetables in the compost is because cooked vegetables usually have salt in them. Unless they make up most of the ingredients, I wouldn't worry about it. I live in an arid climate, where salinity can be an issue, but I wouldn't hesitate to put cooked vegetables in the compost.

When I have a hot compost pile going, I'll even add meat every once in a while. If I add meat, I always make sure it's in the center of the pile, and I only do it if the compost is really hot. Under the right conditions, in a few days, the meat is no longer recognizable.

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