Compost Basics and the Science Behind Composting
An interview with Courtney Gallaher, Ph.D., NIU Sustainability Coordinator and Associate Professor in the Department of Earth, Atmosphere and the Environment
Spring is here, and our gardens are waking up. NIU’s Edible Campus program is raising funds to build a composter, and here at NIU STEAM we’re planning a new sustainability careers summer camp.
That’s why this seemed like a great time to learn about the science behind compost and the basics of getting started! We interviewed soil scientist and sustainability expert Dr. Courtney Gallaher to learn more.
Don’t worry if this sounds a little intimidating! You don’t have to be an expert to start your own garden compost. “Composting and gardening should be fun activities,” Dr. Gallaher says. “The best way to learn is to just start.”
Composting can be fun for the whole family! Dr. Gallaher’s children harvested potatoes grown in big containers of compost.
Why is it good to compost?
There are a lot of reasons to compost! From the perspective of environmental sustainability, it offers a positive alternative for what to do with your food scraps.
One of the biggest problems with putting your food in a trash can is that it goes into a landfill. In the landfill, it goes through anaerobic digestion and releases methane into the air, which is one of the most potent greenhouse gases.
If we compost our food, it goes through aerobic digestion instead. Aerobic means the microbes have oxygen to breathe in, so they produce carbon dioxide instead of methane. Carbon Dioxide is a way less potent greenhouse gas, plus the carbon dioxide gets taken up by your plants when they grow, so the process ends up being carbon neutral.
Your compost also turns into nutrients you can put back into the soil. It makes a really rich fertilizer that you can put into your gardens.
As a side note for our elementary audience, what are some other things that produce methane? Are cow farts one of them?
Yes, they are! Actually, the microbes in everyone’s guts produce methane that is released through burps and farts, but ruminant animals like cows produce much more because of their diets and the microbes that live in their digestive tracts. Cows have lots of special microbes in their rumens, called methogens, that are good at digesting plant materials that other animals can’t use. The cows absorb the nutrients, and the microbes release methane gas as a byproduct. So cow farts are full of methane, and so are cow burps!
You mentioned that compost is a nutrient-rich fertilizer. What are some of the nutrients in compost, and why are they important?
For humans, when we talk about nutrition, a lot of people are familiar with the three macro nutrients: carbohydrates, fats and proteins.For plants, the macro nutrients are nitrogen, phosphorus and potassium. Those are the main minerals without which a plant will die.There are also all sorts of micronutrients that plants need, just like humans have to get other vitamins and minerals.
Compost tends to be high in micronutrients, and also high in nitrogen. So it’s feeding your plants really well by cycling that nutrition from your food or yard waste back into the soil.
How can people get started composting at home?
I’ve worked on composting systems all over the world, and they can be as fancy or as simple as you want them to be. They can literally just be piles of yard waste and food scraps! As you pile stuff up, the bacteria will start to break it down and it will eventually decompose.
There are things you can do to take care of it more intensively that will produce higher quality compost in a faster period of time, though.
One common system is a three-bin compost system where you’ll put your food scraps and your plant waste into one side – let’s say the left side of the three-bin system. Then every few days you turn it, and about after a couple weeks you might move it to the middle bin, and then keep adding into that first bin. Then you rotate through, so that after about 45 to 60 days, by the time you get the third bin, you have nicely composted materials. In colder climates, like northern Illinois, this process may take longer. (Check out our guest blog with Jessica Cima, the curator of the NIU’s Pick Museum of Anthropology and an avid home gardener, to see how the Cima family has set up their three-bin compost system.)
One popular method of gardening is called lasagna gardening, where you just create a raised bed layer by layer. On the bottom you put a layer of cardboard over your grass and then you just layer food scraps and grass clippings and leaves a couple of feet high, and then you plant right into that and it just composts underneath your plants. The years I’ve done that I’ve had bumper crops in my vegetable gardens.
How long does it take scraps to turn into compost?
How long something takes to break down depends on the weather (temperature and moisture) and how finely chopped up it was in the first place. I tend to be a fairly lazy composter in my home environment, so if I’m cutting up vegetable scraps in my kitchen, for example, I don’t dice them up to put into my garden compost. I just dump the whole thing in there. Sometimes, if we haven’t gotten to a melon on our counter and it starts to rot, the whole melon goes in. It takes a little longer, but it does break down.
My mother’s a very fastidious composter! So everything gets finally chopped and her compost is much prettier than my compost. But both still work just fine.
What are some other ways to care for your compost?
You can pay attention to the composition of what you’re putting in there. Bacteria need a specific ratio of carbon to nitrogen to do their best job composting.
Food scraps, grass clippings, green things – all that tends to be quite high in nitrogen. High carbon things tend to be brown leaves, leaves that you’re raking up at the end of fall, or weeds that you pulled out of your garden or whatever scraps you clean up from your garden.
So if your compost isn’t acting the way you want it to – if it smells bad or it’s too wet – you can add more of one type or more of another, and tweak the composition. If you alternate layers – food scraps, plant clippings, food scraps, plant clippings – that just kind of naturally takes care of it.
Even though composting has a lot of chemistry to it, you don’t need to be a chemist to compost! You can just tweak it as you go along.
What’s OK to put in compost, and what isn’t?
As far as food scraps that are acceptable to put into home compost: fruits, vegetables, plant scraps, coffee grounds, eggshells, those sorts of things are fine.
You’re often advised not to put dairy products or meat products into your compost only because they can attract animals. It’s not that they’re not compostable. They are definitely compostable. But in a home environment, experts often advise you not to put them in, whereas with municipal composting systems, everything goes in. But again, I’m kind of a lazy composter, so like, if dairy’s been mixed into a meal, it just goes in the compost.
I hear that compost has to get up to a certain temperature. How hot does it get and why is that important?
It doesn’t actually have to get up to any specific temperature – it just does! Because when the bacteria are doing their jobs, they’re releasing energy, and the energy creates heat. How hot it gets really depends on how attentive you are to your compost and therefore how active are the bacteria in the compost.
It also depends on how big your compost pile is. Big municipal compost piles might get up to about 170 degrees Fahrenheit, whereas your home composting pile might get up to 120 or 130 degrees.
What else is important to make sure your compost is healthy?
Aerating your compost is important because that’s giving oxygen to the bacteria. Aerating just means turning the compost to give it more air, whether you have a barrel, a pile or a three-bin system.
What options are there for people who don’t have room for a composter in their yard?
For people who can’t compost at home, a lot of cities now have composting programs and they’re able to use that in their city parks or gardens, or they sell the compost to customers. In DeKalb, residents can add food scraps to their yard waste bins during collection season.
Another option is vermiculture – worm composting that can be done indoors in a bin.
Worms! Tell us more about worms, please.
Worms are amazing. I was terrified of worms as a child, but I’ve come to appreciate their role in the garden.
In most healthy compost systems, you’ll find some worms that have found their way in because it’s nutrient rich, and the worms have to eat that organic matter as their food source. Then they’ll concentrate it and poop it out as worm castings – and those are super dense little doses of fertilizer.
Worms also help to aerate the soil, to turn it and provide oxygen. And they also create these tiny channels that water can run through. So that again helps to water your compost system or allow water to drain into your garden soil and to move nutrients around.
Vermicomposting is a really fun science project to do with kids and a very effective way of home composting. You can even do it inside in the winter.
What’s happening on NIU’s campus with composting?
NIU’s Edible Campus has a vermiculture system set up, and they’re also raising funds March 20-21 to build a three-bay composter. So those two types of composting will be happening, providing a significant portion of the compost needed for the NIU Edible Campus gardens.
Then long term, one of the things that we’re trying to set up is a food waste composting system for all of campus dining. NIU produces about 700 pounds of food waste per day. And that’s mostly the food out of campus dining that people didn’t finish on their plates – because campus dining’s already doing a good job trying to avoid food waste in the back of house.
Likely for logistical reasons, so we’re not transporting a lot of food waste across campus, they would go into an electric biodigester system. These systems are aerobic (there’s that word again!), so they use oxygen, they’re thermophilic, meaning that they get really hot. The electric compost system is designed so that the food waste passes through it in about two days instead of 60 days.
What else should we know about food waste and compost?
About 40% of food produced in the US is wasted. Some of it is wasted, of course, on the production side. Sometimes it’s left in farm fields. It’s wasted in grocery stores because produce they don’t sell gets put in a landfill. But there is just an astronomical amount of food waste coming out of households, and even people who try to be careful still have food waste. So composting is a really sustainable option for disposing of food waste.
I love compost and I love talking about compost because I have two degrees in soil science. I think soil is everything – it literally allows us to live!
But you don’t have to know anything about soil or anything about gardening to be a successful composter. You just have to try it, and the system can be as precise or as messy as you want it to! Eventually the food will all break down.
Lesson for All Ages: Make a Worm Composting Bin
Making and feeding a worm composting bin is a great activity for pre-school through grade 12. Check out this activity from kidsgardening.org for detailed instructions and materials list. It’s also great to try at home!
Resources for Composting at Home
Here are a few of Dr. Gallaher’s favorite resources to help you compost at home or learn more about the science behind composting.
- The Rodale Institute: Why Compost – The Rodale Institute is one of the founding research institutes of modern organic farming. Check out their website for more details on why and how to compost.
- The Rodale Institute: Backyard Composting Basics – When Dr. Gallaher interned with the Rodale Institute after college, she was helping farmers in Senegal set up composting systems. But the institute also offers instructions for how to compost right in your own backyard.
- U of I Extension: How to Begin Composting Webinar – The University of Illinois extension is a great resource for gardening, composting and soil health right here in Illinois! Check out their website for instructions and webinar recordings.
- Scientific American: How Food Waste Turns into Huge Amounts of Greenhouse Gases – By following specific foods through their entire life cycle, researchers have determined just how much wasted food adds to emissions through phases such as harvest, transportation and disposal. Check out this article from Scientific American to learn more.
If you found all this compost science as fascinating as we did, check out our new sustainability careers summer camp for high school students!
