Does a compost bin need a lid?

compost bin with a lid

QUESTION: Does a compost bin need a lid? I see some models have them, and others don’t. – Joanna C

ANSWER: As you’ve seen on the market, it’s not absolutely essential for your compost bin to have a lid—your compost materials will decompose with or without one. However, being able to cover your compost bin comes along with so many benefits that you really should put a lid on your compost. (If you don’t have a lid available, you can always use a tarp weighted with rocks or a piece of Hessian-backed carpet instead.) Here’s a list of the reasons it seriously benefits you to cover the top of your compost bin.

Controlling pests

A securely fitting lid is your first line of defense against rats, mice, opossums, raccoons, and all the various pest animals that would love to get into your compost bin for a smorgasbord. When the lid is closed and the compost bin is properly managed, all those food scraps inside shouldn’t even be on the local wildlife’s radar. Allowing some animals to enjoy a meal from your compost may not seem like such a big deal—it’s not like some little rodents will be able to consume enough of your materials to really put a dent in the pile, anyway—but with a consistent food supply like compost provides, those pest animals won’t just be occasional visitors. Also, assuming your compost bin is set up in close proximity to your home, it’s a good idea to keep pests as far away from where you live as possible. (After all, you know what they say: If you give a mouse a cookie … )

Managing moisture

It’ll take a whole lot longer to get from a heap of food scraps and garden debris to the final product without a lid on your compost bin simply because you won’t be able to effectively manage the moisture level of your materials. The hydration of your compost will be left up to the whims of Mother Nature and will depend on how rainy or sunny the weather is each day.

Your compost ingredients will still undergo the process of decay (eventually), but when things are too wet, excess water is slower to drain out of the bin, and oxygen has trouble circulating to help dry things off. When your ingredients are too dry, the microbes that do the work of decomposing your compost ingredients will slow down to a creep. The easiest way to adjust the hydration level in your compost is to prop up the lid when the materials get too wet so the sunshine can dry things out.

If you don’t have a lid, every time it rains, your compost ingredients will get soaked, and you’ll face the challenge of drying your compost out over and over again. Then, once you get the compost to the desired level of dampness, if you can’t close the lid to keep moisture inside, a sunny day will just dry things out again in short order.

In other words, without a cover on your compost, you won’t be able to adjust the moisture level of the materials inside the way you really need to. Even if your compost bin is located under an awning or inside a structure like a shed that will protect it from the elements, the process of adding the compost ingredients will also result in fluctuating hydration levels, and without a lid, your moisture management options will still be limited.

Addressing disagreeable odors

Even the most meticulously managed compost arrangement is bound to produce an unpleasant odor occasionally, as a result of too much moisture or too little oxygen. As with regulating the moisture level of your compost, addressing these stinky imbalances is easiest done with the help of a lid on your compost bin.

Regulating temperature

The temperature of your compost is directly linked to its health and how well it is functioning, and the outdoor temperature does affect the temperature of your compost, even when it’s heated up and really cooking. Without a lid on the bin, your compost materials are going to be exposed to the temperature variations of the great outdoors.

When you have the ability to close the lid over your compost, you’re creating a mini-ecosystem that has some protection from the elements and will have a more stable climate as a result. According to Cornell Cooperative Extension, “temperature is a key parameter determining the success of composting operations.”

Case in point: When the temperature gets too high, the fluctuation can result in the beneficial microbes that decompose your compost materials dying off. Another way temperature comes into play when you’re making compost is when it comes to reducing pathogens.

You need a five-day period with temperatures no lower than 104 degrees Fahrenheit (40 degrees Celsius), including a period of at least four hours when temperatures get above 131 degrees Fahrenheit (55 degrees Celsius) in order to significantly reduce the pathogens compost can otherwise contain, kill off fly larva, and take any weed seeds that have made their way into the compost out of commission. Without a lid, it’s difficult to manage the temperature so you can reap all these benefits. 

Does a compost bin need a lid?

Once your compost has finished its decomposition process, you should put the lid on the container and leave it shut. Without the ability to do this, your compost will continue breaking down past its completion point, losing potency and becoming less effective the longer it’s exposed to the elements. Without a cover to preserve the completed compost, it will actually begin to seep into the soil underneath and around it, along with the nutrients that make it so valuable in the garden. Don’t let your months of effort creating that “black gold” go to waste and literally fade away simply because your compost bin doesn’t have a lid.

Speeding up the process

Compost that’s made in a container that has a cover is ready to use more quickly than compost made in a container without a cover. That’s because a covered container tends to hold more heat, and heat encourages the microbes that decompose your compost materials to work more quickly. Making your compost in a bin that has a cover can save you weeks or months, so your compost will be ready to fortify the plants in your garden more quickly, and you’ll get to see the rewards of your work that much faster.

Composting when it’s cold outside

Whether or not this point applies to you depends on the region where you live. In areas where the winters get chilly enough, compost piles eventually freeze through, and the work of the microbes that break everything down stops until temperatures warm up again in the spring. While you can’t do much about the weather in your part of the world, by using a cover on your composting container, you can keep the temperature inside the bin warm enough to keep your compost going in full swing all winter long, no matter how cold it may get outside.