Green stuff, brown stuff: Secrets to a great compost pile

[MUSIC PLAYING] IRA FLATOW: Hi. I’m Ira Flatow. And you’re listening to Science Friday. My yard is finally coming back to life. There are plants budding and blooming. And it’s got me eager to get out into the garden. And if you’re a gardener like I am, you really can’t think about getting your soil in shape without thinking about adding compost.

Composting is a sometimes mysterious process for a lot of us. But it can help get your garden or your yard on its way, both dealing with wastes and giving your soil a boost. So here to help break it all down– bad composting joke, sorry about that– is Cassandra Marketos, a composting aficionado and author of the new book Compost After Reading– A Practical Manifesto for Purposeful Decomposition. Welcome to Science Friday.

CASSANDRA MARKETOS: Hi. Thank you.

IRA FLATOW: Tell me what purposeful decomposition means.

CASSANDRA MARKETOS: I think purposeful decomposition is how I chose to define the composting process. Everything in the world breaks down of its own accord without our interference, for the most part. The idea of becoming a composter means that we’re getting involved with that process. So that’s where that little subhead comes from.

IRA FLATOW: How is it different from just a pile of rotting stuff?

CASSANDRA MARKETOS: Well, it depends on what type of composter you want to be. I definitely know at least a few composters who just keep a pile of rotting stuff and call it a day. It’s not on me to judge them. But the idea of compost is that we, as people, are providing an ideal environment for decomposition for all the little microbes and fungi that are responsible for breaking things down in this world and helping them turn into new life forms. So the idea of a compost pile is that you’re providing the correct ratio of nitrogen to carbon for microbes and fungi to feed and reproduce, which is the basis of all decomposition.

IRA FLATOW: Let’s go to the ABCs of composting, shall we? They say you need some brown stuff. You need some green stuff. You need your leaves and your lawn clippings. What’s going on there?

CASSANDRA MARKETOS: The two items you just described are high-carbon and high-nitrogen inputs, as they call them, for compost piles. Dried leaves are a great example of a carbon-heavy input for compost. And fresh green grass is a great example of a high-nitrogen input. So if you put those things together, you’re creating that balanced ratio that every compost pile needs in order to create an ideal environment for decomposition.

IRA FLATOW: So what should I not put in my compost?

CASSANDRA MARKETOS: That really depends on who you are and where you’re composting. I would say as a definitive rule, don’t put plastic in your compost. Don’t put items that are full of toxic chemicals or primarily made of plastic.

If you are composting in an area with, for example, abundant wildlife, such as bears, I would say don’t compost meat and dairy. But if you’re composting in a backyard in suburban Los Angeles, like where I would live, I would say go ahead and experiment with those things. It really just comes down to where you live, who you are, what kind of compost you’re trying to make.

IRA FLATOW: You brought up urban composting. I’m glad you went there because there are a lot of people who don’t have the room for a giant pile with chicken wire surrounding it, right?

CASSANDRA MARKETOS: Yeah, that’s very true. I didn’t have the room for a big compost pile when I first started composting. I had this teeny, little 3-foot-by-2-foot space between my deck and my house when I first started. But that was big enough to get a compost pile going that was very productive for me. So you don’t need a lot of space, I would say. You really don’t.

IRA FLATOW: And how do you know if you’re doing it the right way? Well, I guess what I’m asking is, what’s going on inside the compost heap that we want to encourage?

CASSANDRA MARKETOS: We want to encourage the growth and flourishing of microbial activity, when it comes down to it. We want those microbes to be eating and multiplying and attracting larger and larger life forms, which are all contributing to the movement of things in the pile, their breakdown, their turnover.

You will know you’re doing it correct when your pile starts to get smaller and its– and those items that you’re adding to it start to change into an Earth-like, crumbly, dark material. It’s very hard to miss when you’re doing it right. It’s also very easy to tell when you’re doing it wrong. When you’re doing it wrong, you tend to get very bad smells.

IRA FLATOW: And does all compost then end up the same, or do you end up with different qualities in the finished product, depending on your starting ingredients?

CASSANDRA MARKETOS: I think if you steward your compost pile well, you’re always going to end up with about the same quality of end product. It really depends on the process, not the inputs, in a home composting situation, for the most part. As long as your ratios are correct and you’re keeping an eye on things, you’re going to end up with a pretty good end product, I think.

IRA FLATOW: All right. Let’s talk about the beginning product because let’s say you’re a novice composter and you want to start composting. What ingredients? What would be the easiest way to start?

CASSANDRA MARKETOS: The easiest way to start composting is to take a look around you on any given day and look at the items that you encounter in your day-to-day that are compostable. For most people, that’s coffee grounds. It’s food scraps from your kitchen. It’s leaves from your yard. It’s trimmings from your plants. It’s things like that. It could even be cardboard boxes that you get delivered to the house. It could be the empty paper towel tube that’s in your

Kitchen. All of those things are future compost inputs if you want them to be. So I actually think the best way to get started is to just do a low-key assessment of your day-to-day life and the items that are in it. You are guaranteed to find at least a few of them that would make a good compost pile.

IRA FLATOW: Now, I mentioned the green and the brown stuff before. How do you decide what goes where?

CASSANDRA MARKETOS: Right. So people use the term “green” in general to refer to items that are high in nitrogen content. It’s mostly food scraps. But it’s also stuff like coffee grounds. It’s things like manure. And for the most part, these are items that are slimy and goopy and oozy in nature. Those are your greens.

Browns tend to be items that are brown in color, hence the name. And they’re things like dried leaves, cardboard, paper, wood chips, things like that. Stuff that’s a little drier and woodier in nature tend to be things that are high in carbon.

And my rule of thumb is that I generally try to keep it two parts carbon-heavy product to one part nitrogen-heavy product in general. People argue about this. They have different ratios that they recommend. Two-to-one seems very easy to eyeball and for the home gardener to keep track of. My goal is always to keep it as easy as possible. And I’m trying not to overcomplicate it for folks. But there is a lot of argument about that.

IRA FLATOW: Speaking of complication and arguments, I know if you’re in the gardening world, we’ve all seen ads for all kinds of bins and gadgets and tumblers designed to make composting easier. Do I need them, or what’s the easiest and simplest thing to do?

CASSANDRA MARKETOS: I personally am not a huge fan of devices to make compost on your behalf. I am not a big proponent of the countertop devices, like the Lomis and the other things. They seem to be very, very expensive for not really making compost for you.

There’s other types of devices that are just like tumblers. Tumblers are very common for beginning composters, as are the single-bin systems that are just a big plastic square that you stick in your yard. And you’re supposed to put stuff in there. Those devices can be useful in the sense that they create a distinct zone in your yard for you to make compost in. There’s a lid. You can cover things. It keeps everything contained for you.

However, I personally specifically really don’t recommend compost tumblers, particularly for the beginning composter. And I get more calls than any other types of calls about people who cannot figure out how to use compost tumblers.

And I think the challenge is that they get compacted. Airflow gets really reduced. You can’t really see into them to see what’s going on with your pile. People forget to turn them. They’re just really tough for the beginning composter to use. And as a result of that, they end up creating all the problems they theoretically exist to prevent. They tend to smell. They tend not to work very well. The digestion is very slow inside of them.

My number one recommendation to all people starting compost is do not get a tumbler. If you really want to get a container, those single-bin systems are much more effective for beginners, in my experience.

IRA FLATOW: What about just setting up a little chicken wire box made out of wood and stuff?

CASSANDRA MARKETOS: That’s way more my preference. I strongly advocate in the book for using found items to build a compost structure with, if you want one. Anything you have lying around that helps you create a couple of walls and a little infrastructure for the pile to rest in is going to be great. Chicken wire is fantastic. Having some wooden pallets, stacking up some bricks, anything that gives you a little bit of shape is going to be effective. You really do not have to go to the store to buy a new thing.

IRA FLATOW: And if you have a– some sort of shovel or a pitchfork, you want to turn it over, right? You want to aerate it?

CASSANDRA MARKETOS: Yeah. Oxygen, as it is to most life forms, is essential for the microbial life in your pile. You want to keep airflow consistent throughout the pile so those microbes are staying alive and propagating happily.

There’s a lot of rules out there about how often you should turn. I would say that once a week or something along those lines is generally a fine rule to follow. If you don’t want to think about it too hard, pick once a week and go for it.

I think one of the number one problems I see with a lot of composters, though, is that they turn way, way too much. And your pile does need a little bit of rest time in order to– for breakdown to stay active and healthy. So you don’t want to overturn. Once a week is generally pretty good.

IRA FLATOW: I know people who have put thermometers and things in their compost heap as a measure of how well it’s working.

CASSANDRA MARKETOS: Totally. I love to see how hot my compost pile gets.

IRA FLATOW: It should get hot?

CASSANDRA MARKETOS: It can get hot. It doesn’t have to get super hot, but it’s really nice when it does. I feel like the hot temp compost is really a badge of honor. Basically, as your compost pile is building microbial activity as decomposition is getting underway, all those little microbes are creating heat as they work. And eventually, that’s reflected in your compost pile starting to actively steam. So it’s really fun to see that. And it’s a sign of really, really healthy and active decomposition.

IRA FLATOW: Are there things that you can add to help the process along, for example? Should I add worms, for instance?

CASSANDRA MARKETOS: You don’t have to. They’ll find their way there. If you have a compost pile in your backyard and it’s touching the earth at the base, if you just leave it alone, worms will find their way in.

There is a type of composting that’s called vermicomposting. That’s specifically worm composting, where you make a home for worms and put them in and then harvest the worm poop. But for the average backyard pile, they’ll find their way into it. You don’t need to add them in advance is my opinion.

IRA FLATOW: How long, then, does the process take to go from a banana peel to decent compost?

CASSANDRA MARKETOS: Boy, I wish there was ever a straightforward answer in compost where I could just say, this is the thing, and that’s what happens. But like all things compost, it depends. It depends on what type of pile you have how long it’s going to take. If you have a single-pile compost in your backyard that you’re very casual about managing, it might take six months to a year before you get finished compost. And that’s totally fine.

If you’re running a more active system, like the traditional three-bin compost system that you see in community gardens, you can get finished compost in six weeks from those. So it really just depends on how active your management is.

IRA FLATOW: After the break, can composting go big time? We’ll talk about municipal composting programs. Stay with us.

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I know that if you can’t do this yourself, some cities and towns have started municipal composting programs where you have a little special bin, a plastic bin, and you collect stuff and you bring it to them, right? Isn’t that a good idea?

CASSANDRA MARKETOS: I do think that’s a good idea. And I really support it in spirit. I think if we want to have a really robust, regenerative, healthy waste management system in this country, we’re going to need municipal support in addition to backyard composting and local community composting efforts. I think all of them are very, very good.

IRA FLATOW: Are there policy things that towns can do to incentivize composting?

CASSANDRA MARKETOS: That is a great question that I don’t know if I have a fantastic answer to. I think that any support that you can get from your city council or community board to fund community gardens is going to be a boon to community composting. I personally work at a community compost that’s part of a local community garden. Anything you can do to support those kinds of systems and those kinds of local programs will benefit composting.

IRA FLATOW: Well, I think that was a great answer.

CASSANDRA MARKETOS: Oh, good. I’m glad. I’m really a fan of green spaces existing in cities for everyone.

IRA FLATOW: Yeah, we love green spaces. All right. So let’s talk about spring is here, and I want to rejuvenate my soil. I’ve got my compost from last year. I’ve made it. I’ve got compost. I have a lot of pots. We all have a lot of pots sitting out on the deck or something with last year’s soil in it from the plants, right?

CASSANDRA MARKETOS: Yep.

IRA FLATOW: I can rejuvenate that soil with compost, can’t I?

CASSANDRA MARKETOS: You absolutely can. This is actually one of the most fun things about using compost, I find. You can have an old pot of dirt. You can incorporate a handful of your finished, healthy compost, wet it, and plant something in it. And you’ll get, for the most part, healthy new plant life from it. It’s really nice.

I always recommend people take their finished compost, make sure it’s finished, and just incorporate handfuls into houseplants or plants that you have on your deck or add it to a garden bed prior to planting. It’s pretty hard to mess up using finished compost, to be honest, when it comes to growing stuff.

So you just really want to make sure there’s no undigested food bits or weird smells coming from the compost. If it really looks and smells like fresh, good Earth, you have good, finished compost. And then you’re pretty good to use it.

IRA FLATOW: Can you start composting too early or too late in the year?

CASSANDRA MARKETOS: I don’t think so. I’m so loosey-goosey about this. If it’s the dead of winter and it’s freezing outside, you might have some trouble getting started. Anytime is a good time to start composting, I think.

IRA FLATOW: Speaking of which, the title of your book is Compost After Reading.

CASSANDRA MARKETOS: Yes.

IRA FLATOW: So are you saying we should compost this book when you’re done with it?

CASSANDRA MARKETOS: I am saying you should compost this book when you’re done reading. I think the goal of writing the book for me was to make you so confident about compost that by the time you’re done, you don’t even need the book. You can compost it away. And you can start on your journey of being an expert yourself.

IRA FLATOW: Does it matter if it has printing in the book or color pictures or stuff? Should we take those out, or just throw them all in?

CASSANDRA MARKETOS: I did recommend in the instructions at the back to not compost the binding because the glue and the binding is– has plastic material in it. So it’s not very good for your compost. But the rest should be good to go in there. Recycled paper, vegetable-based inks– everything should be good to go.

IRA FLATOW: All right. So just sum up for me, what are the big things you see people doing wrong, the common mistakes they’re making in composting?

CASSANDRA MARKETOS: The really big one is that people think compost is synonymous with just a bunch of rotting food, and it’s not. You will not get a good outcome if you just pile up a bunch of rotten food in your backyard and leave it alone. You have to mix it. You have to mix that food waste, that green with the browns. And you have to keep things in balance. That is the compost that you want to make.

The other big mistake I see people making is they put their food waste just on top of the pile and leave it there and walk away. That’s a recipe to attract a lot of flies and to create a lot of smells and to maybe get a lot of animals. So you want to make sure every time you add food waste to cover it with some form of brown, whether it’s food scraps or torn up cardboard or anything you have on hand. Just make sure you’re covering the food waste. That will help manage any issues around the pile you might be worried about.

IRA FLATOW: That’s a very good tip. Well, thank you. Thank you, Cassandra, for taking time to be with us today. Thank you for that book. I’m going to read it and then take it out to the backyard.

CASSANDRA MARKETOS: If you compost it, you’ve got to send me a photo. No one will compost the book. Everyone says they love the title, and then none of them will compost it. So if you do it, you got to send me photos.

IRA FLATOW: Cassandra Marketos is a composting aficionado and author of the new book Compost After Reading– A Practical Manifesto for Purposeful Decomposition. And if you want to read an excerpt from the book, it’s on our website at sciencefriday.com/compost.

If you’ve got a topic you want us to breakdown, leave a note for us on the listener line, 877-4-SCIFRI. This podcast was produced by Charles Bergquist. Thank you for listening. I’m Ira Flatow.

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