How to Compost Food Scraps

Keeping food scraps for composting serves two important purposes. It diverts the waste from landfills and the compost provides beneficial organic matter to support plant growth in your garden. Depending on how you manage it, the process may be “fast” or “slow” or something in between.

If you’re curious about compost tea, see Should I Use Compost Tea? for more.

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Getting Started With Composting

I grew up in a composting household so keeping kitchen scraps for compost has been a lifelong habit.

It wasn’t until I met other gardeners as an adult that I realized composting methods can vary so greatly.

Methods range from casual and slow to methodical and relatively fast. Or somewhere in between (like I do it).

But, no matter which way, if the basic principles are followed, it all seems to work. The difference is simply how soon the compost will be ready for your garden.

Realistically, most of us never know the science, just do what we can when we can, and it all works out.

If you’re worried about attracting rats or other pests, this shows the closed tumbler composter I like.

And do not worry about smell. If you follow the basic tips here, your compost pile will not stink.

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Contents

• Why Compost Food Scraps?
• How Composting Works
• Routine & Maintenance
• Ready to Use
• Resources

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Why Compost Food Scraps?

My main reason for composting may surprise you. As much as I love adding compost to my soil, the chief concern is keeping food waste out of landfills. The fact that homemade compost improves the garden is a total win.

In my old garden, the clay soil was so tough I could not get a shovel in it. Over the years, I simply added compost on top. Eventually, it built up to a depth that allowed me to plant and grow anything I wanted.

Now I’m faced with almost pure sand. Again, the only remedy has been to mulch with wood chips and add compost on top.

In my first year of gardening here, I never even saw a worm in the soil no matter how much digging I was doing, including installing a pond! Nothing but sand.

Now, years later, as I add layers of fresh compost each year, there are signs of life in there. Compost introduces decomposed organic materials into the soil, providing nutrients for plants. And the entire microorganism and macroorganism crew come along for the ride, bringing the soil to life. It also helps retain water, which is critical in super sandy conditions like mine.

Let’s walk through the ideal composting method. Realistically, you may not be able to consistently maintain it this way, but the more you can stick to best practices, the sooner you’ll have compost ready to add to your garden.

How Composting Works

A compost pile is a living thing and requires ongoing inputs and care. If you want to produce compost quickly, follow these principles as closely as possible, and do more reading to further understand the science, so you’ll know how to adapt as needed.

Factors Affecting Compost Process

When we achieve the optimum balance, the microorganisms that thrive in higher (but not too high) temperatures (aerobic bacteria) make fast work of the decay process, providing lovely compost in a matter of weeks.

If the process is interrupted, the temperature drops, and less efficient bacteria (and others) take over. It still works eventually but progress is slower.

The cooler seasons will also temporarily slow the process.

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Two Main Ingredients

To keep it simple, we divide the ingredients into two camps.

They are not all truly brown or green in color but it’s a helpful system for remembering what’s what.

The smaller the pieces, the faster the materials can be broken down.

I avoid adding anything with suspected pest- herb- or insecticide exposure, animal waste or manures, cooked foods, oils, fats, cheese, meat, bones, diseased plants, or invasive seeds.

This minimizes the chance of attracting wild animals to the pile and reduces worries about various pathogens and other nasties.

If you want to compost some of these other items, do your homework first to keep it safe.

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Microorganisms and Compost

It takes a village. There are countless organisms at work in a healthy compost pile.

Microorganisms (chemical decomposers) including bacteria, fungi, and actinomycetes.

• Aerobic bacteria are the most efficient compost-makers, excreting nitrogen, phosphorus, and magnesium. Many types are present and active, depending on the temperature of the compost. Thermophilic bacteria are active during the sweet spot period (113-160°F). If temperatures cool, the lower-temp-loving-less effective bacteria take over. Actinomycetes (higher form bacteria) give compost that lovely, earthy smell.
• Anaerobic microorganisms take over if oxygen levels drop below 5%. With lack of oxygen, the greens can ferment and become stinky due to the production of acids, hydrogen sulfide, and more. This is why you have to turn the pile: it lets fresh air in.

Macroorganisms (physical decomposers) are also on the team.

• Examples include ants, beetles, centipedes, earthworms, flatworms, flies, millipedes, mites, nematodes, sow bugs, snails, springtails, spiders, slugs, rotifers. Go, Team!

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Ratios: Carbon to Nitrogen (Brown to Green)

Some research indicates a 30:1 ratio of carbon (C) to nitrogen (N), based on dry weight, is the sweet spot for a healthy, fast-producing compost pile. This is the ratio where the deluxe microbes grow best and can make fast work of converting all those greens and browns into compost.

For organic certification, a ratio between 25:1 and 40:1 is required, allowing more leeway.

With too much carbon (greater than 30:1), heat production drops and the process slows down.

Too little carbon, and the compost ferments, gets stinky, and loses its nutrient value.

But what does this mean and how do we achieve this?

This is where the simple, slower methods, and the fast, accurate method part ways.

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Slow Method

Most of us make somewhat educated guesses for ratios of browns and greens.

Here’s what I do.

For every pound of greens, I try to add approximately 3 pounds of browns.

1 pound of greens | 3 pounds of browns

No, I don’t weigh or measure. This is my estimate based on what I’ve been doing instinctively for a long time. I also tend to compost the same greens (fruits and veggies) throughout much of the year. Yours may be different and have higher or lower nitrogen levels and you may need to adapt it. But, for the sake of simplicity, finding a method by volume or weight keeps it simple.

I know the ratios are on target by look, feel, and temperature of the pile. If I can see things are decomposing and it’s not stinky, it’s doing fine. Again, it becomes instinctive. Just get started. You will get it as time goes on.

If you are trying to understand how the 30:1 C:N ratio translates to this practical formula, it’s a big topic and open to debate. I’m sparing you the amateur (by me) chemistry lesson, to keep it simple, but basically, the chemical composition of each item varies (of course), so we generalize it. There are links (below) if you’d like to explore this further.

Because I have greens to add every day, I keep bags of fall leaves nearby (saved from autumn raking) so I have browns available to balance the ratios in the bin. And it can be that simple for you too.

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Fast Method

What the compost geeks do is learn the individual ratios of everything going into the pile (the actual carbon to nitrogen ratios vary with every single item) and add more of what’s needed to achieve the ideal 30:1 ratio or close to it. When done right, compost can be ready in just a few weeks, and that is a lovely reward for any gardener.

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Other Factors

Moisture: 40-60%

If you are in the right ratio range, there will be adequate amounts of moisture present, simply because of the water contained in the greens. I do have to water my compost pile very occasionally during heat waves when a lot of moisture evaporates but otherwise find this to be true.

When adequately moist, the compost feels like a rung-out tea towel in your hands: moist but by no means dripping wet when squeezed.

Oxygen: 5% minimum

For the aerobic bacteria to go to town, oxygen levels within the compost need to be at least 5%. This is achieved by turning the pile 1-2 times a week. Slightly bulky materials in the pile also provide air pockets.

Temperature: 160°F

I’ve noticed some variation in the research, but, most commonly, 160°F (70C) is named as the maximum desirable temperature (at the warmest part of the pile), which is the marking point when the aerobic bacteria stop working or slow down.

How to measure?

I use the old-fashioned way: stick a metal pipe deep into the pile and pull it out. If it has heated up, you know the bacteria are doing their thing in there.

I have a neighbor with a really large compost pile and I can tell when it’s getting really hot inside because their cat will nap on top—even on a cool day.

Compost Thermometer | Amazon

If you do want to measure, our compost geek friends recommend using a compost thermometer. Make sure you get one with a long probe (20-inches) and a high range (over 160°F). You can use the same thermometer for checking soil temperatures for seed sowing as well.

• 90-160°F indicates the compost process is working.
• Above 140°F will kill off unwanted pathogenic organisms and weed seeds. This is good.
• Over 160°F, compost may become sterile and no longer fight diseases.

Pile Size

One cubic yard is ideal for maintaining heat but still manageable for turning.

I have some neighbors who are vehemently against composting and to avoid their wrath, my main compost area is a compost tumbler. I had my doubts when I got it, but it does work very nicely. For this type of composter, I suggest adding several buckets full of good garden soil when starting out to ensure there are microbes present.

An open pile is ideal for easy management but may not be the best option if vermin (or neighbors) are an issue.

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Routine & Maintenance

Ideally, you add new materials and turn the pile every 3-4 days during the growing season. This provides fresh air for the aerobic bacteria.

In reality, many of us do not have the time.

So, what happens?

A dormant pile will lose its heat, downgrading to less productive bacteria.

When you add additional nitrogen and carbon suppliers, and turn the pile, things perk up again.

Again, the world will not end if you neglect your compost pile. It just means the process is slowed.

The important part is that you continue to add your food scraps (greens) and turn the pile and add browns as needed when you can.

And yes, you can continue adding scraps in winter. Everything will freeze and the decomposition process will resume when the warmer seasons return.

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Ready for Use

When compost is ready for use, it looks, feels, and smells like good, earthy dirt. Hold it in your hands: it is beautiful and well worth it.

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Resources

Listen

Sources | Read More

• Oregon State edu | How to encourage a hot compost pile
• Penn State edu | Home Composting: A Guide for Home Gardeners
• Cornell edu |  Compost Physics at compost.css.cornell.edu/physics.html
• Planet Natural | Carbon-to-Nitrogen Ratios

~Melissa the Empress of Dirt ♛