Already been mentioned that compost is excellent for enhancing nitrogen content, opening up the texture of your soil, and increasing organic matter levels. Now let’s take a more in-depth look at composting, in terms of what it is and how to do it.
What Is Composting?
Composting is a natural process of recycling organic materials and turning them into fertilizer. It’s what would happen to the organic materials if we just tucked them into a vegetable bed or laid them on the ground, but we can do various things to speed up the decomposition process compared to what would happen in nature. A good compost heap provides an ideal environment for worms, sowbugs, fungi, and microbes to break down the organic materials, and will produce dark, rich organic matter that’s full of nutrients. That end product can be used to amend almost any type of soil and keep it healthy and fertile.
Composting is good for the environment as well. Food scraps and garden waste account for 28% of all household waste—in fact, according to some estimates, 30-40% of the US food supply is wasted. By putting your scraps in a compost heap, you’re keeping them out of the landfill. You’re cutting down on all the transport and treatment costs. Soil that’s been treated with compost will help to filter water on its way into the watercourses and will also resist soil erosion and water runoff. And you’re also directly cutting down on greenhouse gases.
Let’s explain that last point. Landfill sites are huge methane emitters. That’s because organic material in landfill sites tends to decompose anaerobically, which creates both carbon dioxide and a huge amount of methane (one of the most powerful greenhouse gases). Organic material in your composter should have plenty of oxygen in it, and aerobic decomposition (which includes the air in the process) doesn’t create these gases.
In fact, creating compost is also a useful way to sequester carbon: it’s stored in the soil instead of being released into the air. So that’s two greenhouse gases killed with one stone!
Anaerobic decomposition in controlled ‘digesters’ can create methane and collect it for use as a fuel or to create heat or electricity. This is eco-friendly, and some municipalities are now operating digesters as part of their waste disposal strategy. But a simple landfill doesn’t have any way to collect the methane, which escapes into the atmosphere. The EPA estimates that methane emissions from MSW (municipal solid waste) landfills account for nearly 15% of the US total.
What Materials To Use For Composting
What materials can you use for composting? Generally, anything that will rot down will work. Obviously, you can’t use plastic or metal, and you shouldn’t use anything with harmful chemicals, such as wood that has been treated or painted. You should also be careful not to use plants that have been treated with pesticide, or diseased plants such as tomato vines that have had blight—those should be burned or disposed of in the trash.
Almost all garden waste can be used. Grass clippings are fine, as are fallen leaves, twigs, and windfall fruit, stalks of vegetables like Brussels sprouts, dead tomato vines, squash plants, and so on. However, if you’re using larger twigs, make sure you chop them up using a chipper (an alternative for small amounts of twigs is to lay them on the grass and run a lawnmower over them a few times, or else chop them up a hand with secateurs or loppers to avoid breaking the lawnmower).
Vegetable food waste can be used. That includes coffee grounds and tea leaves or tea bags, as well as vegetable peelings, strawberry hulls, and so on (although note that many tea bags are still made from plastic and can leave microplastics in the soil). However, animal-derived food waste including dairy products should not be used, nor should oils, fats, or grease. And don’t use cat or dog litter—cats and dogs are omnivores and can transmit some nasty diseases in their excreta. On the other hand, if you have herbivorous animals like goats, horses, rabbits, or chickens, you can use the manure and bedding in your compost.
Cardboard and newsprint can go in the compost. But cardboard that has been coated with plastic, and very glossy paper, is not a good idea. Send those to the trash can. The glossy paper uses a lot of adjuncts such as kaolin and titanium dioxide to create that glossy surface, so there’s not as much wood cellulose in it as you’d think.
Finally, watch out for allopathic plants like black walnut. Walnut leaves and twigs contain juglone, which is a growth inhibitor. If you compost this, you’ll have a compost that other plants won’t want to grow in.
And don’t put weed roots or seeds in the compost (unless hot composting)! On the other hand, if you chop down weeds like nettles before they go to seed, use them as a free source of nutrients.
| Can be composted | Don’t compost |
| Cardboard, paper (except glossy) | Plastic |
| Tea bags | Cooked meat or bones |
| Coffee grounds | Plants with the disease, especially blight |
| Grass clippings | Dairy, meat, and egg products |
| Fallen leaves | Plants that have been treated with pesticide |
| Twigs, shredded bark | Black walnut tree leaves/twigs |
| Manure from herbivorous animals | Baked goods |
| Cotton, wool | Manure from carnivorous/omnivorous animals |
| Crushed eggshells | Wood/sawdust treated with chemicals |
| Hair, fur | Glossy papers |
| Hay, straw | Plastic-coated cardboard |
| Nutshells | Weeds that have gone to the seed |
| Cornhusks, vegetable peelings | Coal ash |
| Wood ash | Fats, grease, oils |
| Dead houseplants, flowers | Cat or dog litter etc |
| Sawdust, wood shavings | Roots of perennial weeds |
| Young weeds (eg nettles) | Disposable nappies |
What Are The Benefits Of Compost?
Compost is a lovely thing because it has so many benefits. First of all, it’s full of organic matter. Incorporating that into your soil will help improve its texture, whether it’s sandy or clay soil. If it’s sandy, the compost will help the soil clump together better and resist erosion; if it’s clay, the compost will help to separate the soil particles and help make the soil more open so that water can flow more easily.
Organic matter is also water-retentive. Just a 1% increase in organic matter will allow an acre of land to retain 20,000 gallons more water. Compost on its own can hold up to twenty times its own weight in moisture.
And compost contains the three main nutrients—NPK—as well as other essential elements, so you should not need artificial fertilizers to boost your soil if you are giving it a regular feed of compost.
What are the benefits of home composting?
You can, of course, buy compost from a shop or garden center. But home composting is actually better, for a number of reasons:
- First of all, shop-bought compost often contains peat. The manufacturers dig up vast areas of peat bog every year. But peat bogs are a habitat for many kinds of vegetation and fauna, a store of rich biodiversity. They also act as huge sponges which help retain stores of water and prevent flooding. And most importantly, peat bogs are huge carbon sinks, capturing CO2 from the atmosphere. We need our peat bogs to help slow down climate change. A peat bog takes thousands of years to create. It’s formed by layer upon layer of marsh vegetation and sphagnum moss all pushing down on one another over time and decaying, very slowly. Once a bog has been destroyed, it can’t be remade—you can’t just ‘plant another tree.’ Major bogs include the Bog of Allen, 370 square miles of bog in the middle of Ireland; Lindow Moss, in England, where the preserved body of the Lindow Man was found in 1984; a huge series of peat bogs in Lapland; Hawley Bog Preserve in Massachusetts; Joseph Pines Preserve in Virginia; and Western Siberia’s huge, frozen peat bogs. Many bogs in the USA and elsewhere have been made into nature reserves, much of the importance of the habitats for specific flora and fauna. So, if you have to buy compost, look for ‘peat-free’ compost and make sure it says exactly that on the packet. Don’t fall for greenwashing: ‘eco-friendly’ or ‘organic’ compost can still contain peat. According to the Royal Horticultural Society, 57% of gardeners don’t know what’s in the compost they bought in the shop—but you should at least be sure of what isn’t in it.
- Of course, homemade compost is also cheaper than buying it in the shop.
- Because you’re not heat treating it or sealing it up in plastic, you’ll have lots of beneficial microbes and earthworms in it.
Composting Manure
If you have access to a lot of manure—for instance, if you live near a stable or keep goats or chickens—you can compost that separately. In fact, manure needs to be composted before you use it on plants, otherwise, the strong concentrations of nitrogen and ammonia can ‘burn’ the plants. If you have small amounts, you can include it in the general compost heap, but a lot of gardeners prefer to compost it separately.
Hot composting manure is a really good idea. Some weed seeds can survive in manure from animals fed on hay or allowed to graze outside; hot composting will kill those seeds effectively, as well as kill off pathogens. Manure will lose about half its volume when composted, so get twice as much manure as the compost you need.
Horse manure is full of nitrogen, so composting horse manure is particularly useful if you have nitrogen-deficient soil, or as an added feed for nitrogen-hungry plants.
Different Ways To Use Compost
Compost can be used in a number of different ways:
- First of all, it can be used directly on the soil as a top dressing
- It can even be sprinkled in small quantities over a lawn to add nutrients to the soil.
- It can be used as a growing medium for seeds and seedlings
- It can be added to potting soil for house plants and container gardens
- It can be used to make compost tea (I will explain how shortly), which can also protect against diseases such as leaf spot
- It can also be used as mulch, and in my view, that’s one of the best ways to use it. If you have nice loamy soil and you dig the compost in, you can disturb the delicate mycorrhizal fungi in the soil. If you just leave the compost on top of the soil, it will break down gradually. However, if your soil is very sandy, or heavy clay, you may need to dig the compost in, particularly the first time you use it, as the soil needs the amendment to work fast.
Adding compost to the soil is one of the best amendments you can make for soil texture. If you’re making a new raised bed, for instance, and you have well-rotted compost available, then make a fifty-fifty mix of compost and soil (don’t use 100% compost, as the nutrients would wash out far too quickly).
While a one-off addition of compost can make a quick and effective improvement, it’s important to add compost at least yearly to keep replacing nutrients. For instance, give your house plants a boost in spring by crumbling a layer of compost on top of the soil in their pots. Rake compost into your vegetable beds and scatter a ring of compost around your fruit trees.
For vegetable beds, you’ll want to use 2-3” a year. It’s best to add half an inch or so in spring to feed your plants and prevent weeds, and then add more in the fall unless you’re using a cover crop.
Compost Tea
Compost tea is easy to make: simply steep a few handfuls of compost in water for a while, then use it to drench the soil. Some gardeners also use it as a foliar spray. Because of the microbes contained in the compost, it’s one of the few times getting the leaves wet might actually be a good idea. (However, there is some concern about e-coli or salmonella microbes getting into the compost tea. You really don’t want that, so it’s probably best not to water your salad plants with the tea).
To get the best benefits from your compost tea, you need to make it aerobically, that is, either bubble air through it or shake it up to aerate every couple of hours.
Compost tea isn’t magic. It won’t increase the number of nutrients in the compost, for instance. In fact, nutrients will be very diluted if you make compost tea. But it is easy to use as part of your regular watering procedure, in between top-dressings or mulches of compost, and is a nice way to ensure that you don’t forget to give your garden a regular feed.
Different Ways To Compost
I think composting is like politics or religion—don’t talk about it with your friends and family, as there will always be an argument!
There are a number of different ways to compost, and it can be done indoors, outdoors, on a large or small scale, with a lot of work or without. There are two main kinds of composting: cold and hot.
- Cold (passive) composting works slowly. It’s good for composting small amounts, but it won’t kill off pathogens or weed seeds. It’s mainly anaerobic (i.e., doesn’t use oxygen in the decomposition process).
- Hot (active) composting works much faster: you might have compost within four weeks with hot composting against as much as two years for cold composting. The high temperatures reached destroy weed seeds and pathogens, but hot composting is harder work, needing more attention (aerating, watering, ‘turning’ the pile).
There is also worm composting, a different process that is particularly useful if you have to compost indoors or on the balcony, as it’s almost odorless and very clean. But for now, let’s talk about garden composting and how to get the best out of your compost pile.
First of all, as you know from previous chapters, it’s important to get the carbon-to-nitrogen ratio right. Ideally, you’ll want to start off with between twenty-five and thirty parts of carbon for each part of nitrogen, which as a rule of thumb needs a ratio of two to four times more ‘brown’ than ‘green’ materials in terms of volume. You should make alternate layers of brown and green; for instance, make a layer of twigs, then grass clippings, then paper and cardboard, then food scraps.
One way to make your life easier is to keep a ready pile of ‘brown’ in a box next to your compost heap. Then every time you put any ‘green’ onto the heap, you can just scatter the ‘brown’ on top of it. If at any point the pile gets smelly, add more carbon (brown); it might also be time to aerate the pile.
Ideally, put your compost pile somewhere that you have easy access to from your kitchen, but is not too close to the house. It’s particularly good if it’s accessible by a concrete or gravel path, so it’s not muddy when it rains. It should be in a shady spot, and relatively dry; remember to cover the top, otherwise nutrients will be washed out by the rain.
| Material – Carbon: Nitrogen ratio | |
| Browns = High carbon | Ashes, wood – 25:1 Cardboard (shredded) – 350:1 Corn stalks – 75:1 Corn stover – 60:1 Fruit waste – 35:1 Leaves (dry) – 60:1 Newspaper – 800:1 Newspaper,(shredded) – 175:1 Peanut shells – 35:1 Pine needles – 80:1 Ryegrass (flowering) – 37:1 Ryegrass (vegetative) – 26:1 Sawdust (hardwood) – 325:1 Sawdust (rotted) – 200:1 Sawdust (softwood) – 600:1 Straw, wheat – 75:1 Wood ashes – 25:1 Wood chips – 400:1 |
| Greens = High Nitrogen | Alfalfa – 12:1 Chicken manure – 7:1 Clover (flowering) – 23:1 Clover (vegetative) – 16:1 Coffee grounds – 20:1 Cottonseed meal – 5:1 Cow manure – 18:1 Finished compost – 16:1 Fish scraps – 4:1 Food waste – 20:1 Garden waste – 30:1 Grass clippings (dry) – 20:1 Grass clippings (fresh) – 15:1 Hay/grass mix – 25:1 Hay, mature alfalfa – 25:1 Hay, young alfalfa – 13:1 Horse manure – 25:1 Human manure – 8:1 Human urine – 8:1 Leaves (fresh) – 30:1 Manures – 15:1 Rotted manure – 20:1 Seaweed – 19:1 Vegetable scraps – 25:1 Weeds – 30:1 |
Chop up your ingredients before they go into the compost pile. For instance, eggshells need to be crushed, not put in whole; twigs need to be chipped, and it’s a good idea to chop up leaves so that the microbes can get at them quickly. If you have a melon that’s gone off, don’t put it in whole—chop it up or squash it.
Active (hot) composting
Active composting is quite hard work, as you need to turn and water the compost. You’ll want your compost to be about as wet as a wrung-out sponge— not dripping with water, but not dried out. You’ll probably need to water it from time to time to keep it wet. You also need to turn the pile over, once a week in summer, and once a month in the cold season. Using a tumbler can help reduce labor, though that will limit the amount of compost you can make.
As the alternative name ‘hot composting’ suggests, you’ll want your pile warm; the optimal temperature is 130-140 degrees Fahrenheit. In winter, you should see your pile steaming gently.
A one-yard cube is an ideal size for a compost pile. It’s big enough for the inside to get nicely hot, insulated by the rest of the compost.
Berkeley hot composting method
This is a particular method of hot composting that needs a lot of material and a lot of work. In return, it’s exceptionally quick, and it kills pathogens and weed seeds. It also reduces the volume of compost much less than with cold composting and retains more carbon and nitrogen in the compost. The speed advantage is amazing, with this method taking just over two and a half weeks from start to finish.
For this method to work, you need to make sure that three conditions are met:
- The temperature needs to be maintained at 55-65C / 131-149F
- The C: N ratio needs to be between 25:1 and 30:1
- The composting material needs to be well broken up
First, build your heap. You’ll want it about a yard wide and about one and a half yards high. Getting the right C: N ratio will mean mixing materials. Lower the ratio by adding high-nitrogen materials like manure or grass clipping; raise it by adding high-carbon materials like straw, sawdust, or woodchips. Try to lay the ‘greens’ and ‘browns’ in quite thin layers. Make sure you build your heap somewhere with a good amount of spare space to one side, so that you can turn the heap over, or else construct several bays to turn the compost into.
Then water the compost heap really well. When it’s saturated and dripping water out of the bottom, you’ve done your job for the moment. Do nothing for the next four days.
Then you need to start the hard work. Take the compost from the outside of the heap and make the core of the new heap with it. Then take the inside of the old heap, which becomes the outside of the new heap. In other words, you’re turning the heap outside to inside and inside to outside.
This means the material that was on the outside and didn’t heat up, is now in the middle of the heap getting nice and hot. The material that was inside, and was hot, will now form the insulation.
Every second day, you turn the heap inside out again. It’s hard work, so try to get some help with it. If you know another gardener, either split the compost or volunteer to help them with their hot composting as part of the deal.
On day seven and day nine, measure the temperature at the center of the heap with a compost thermometer (you can use a cooking thermometer too, but you probably won’t want to use it for cooking afterward). The heap should be at the correct target temperature on these days as it will have got properly started, and it will still have plenty of organic material to work on. Later on, as the organic matter gets scarcer, the heap may cool down.
If your heap isn’t hot enough, then when you next turn the heap, add a handful of blood and bone fertilizer for every forkful of compost that you turn. If the heap is too hot, or if it’s smelly, add some sawdust—again about a handful for each forkful of compost.
Yes, it’s hard work. But on day eighteen, your pile should be finished, and you can use your compost whenever you like.
Passive (cold) composting
This is a much less labor-intensive way of composting. You simply build a heap and let it rot. This might not kill weed seeds, so you have to be a bit more careful about what you put in the compost heap. You might also want to poke the heap from time to time to let some air in. Or you could add some piping, put a large, perforated plumbing pipe down the middle, or just poke larger sticks through to introduce airflow in the pile.
Cold composting is more useful if you’re just composting small amounts of household and garden waste. Hot composting really needs to start with a large amount of waste; if you compost cold, you can just add materials as and when you have them ready.
Building your compost bin
It’s quite easy to buy a compost bin from a garden center, or online. Some communities provide subsidized compost bins for residents to help reduce waste, and this can be a good way to get started. But you can also make your own compost bin.
Simple and cheap compost bins can be made out of recycled materials:
- Make four walls of pallets or logs
- Use big plastic containers. Perforate the bottom (earthworms will make their way in) and make sure you use the lid
- Use an old trash can. Drill holes in the bottom and sides
- Sink four large posts in the ground, in a square, and stretch chicken wire between them to form the walls
- Use straw bales for your ‘walls’
- Make a smaller, cylindrical bin by just cable-tying chicken wire or mesh into a cylinder. For best effect, line the sides with cardboard, moss, or leaf mold
If you’re composting mainly food scraps, rather than garden trimmings, rodents can become interested in your compost pile. It’s best to choose a bin that is fairly closed in this case; for instance, a trash can with tiny holes in the bottom is better than a fairly open pallet-sided bin. You can build one bin but real luxury is having three bins: one that you’re adding to, one that you move the compost onto once the fill-up bin is full, and one for finished compost.
When Is My Compost Ready?
People often don’t know when their compost is ready to use. But once you’ve seen good compost, you won’t have any doubts. When it’s ready, it’s crumbly and soft in texture, dark in color, and reduced to about a third of the original volume. You won’t be able to see any scraps of organic material left in it—no twigs, no bits of the stalk—because it should all have rotted down perfectly.
And it should smell nice. Imagine, for a moment, that it’s a nice spring day, and it’s been raining, but now the sun has come out. You’re standing on a path by a little wood and you go into the wood, and you can smell the damp earth where it’s rained, and the fresh leaves. Or maybe imagine you just watered your tomato plants and you can smell the wet earth where you’ve been watering. That’s the kind of smell finished compost ought to have.
If it smells gross, it’s not ready, and you’ve likely done something wrong. It’s probably best to mix in a good helping of carbon, like a ripped-up cardboard box or bark chippings, and leave it another few weeks before you take a second look.
Trench Composting
An alternative to having an above-ground compost pile is to dig a compost trench. The hole needs to be at least 1’ deep, or 2’ if you can manage to dig that deep, and you simply place the compostable material in and cover it back up with soil.
This has the advantage of being odorless and invisible once it’s been filled. The disadvantage is that this compost isn’t easily movable elsewhere in the garden, so you will want to dig where you want the nutrients to be available. For instance, if you are going to plant a tree or a line of redcurrant bushes, that would be a great place to put a trench, as would the center of a planned vegetable bed.
Because you want to dig, fill and cover the trench quite quickly, trench composting is most suited to single-time deposits such as fall yard waste, or cuttings and clippings generated when you’re getting to grips with an overgrown garden. A big advantage of trench composting is that it gets composted down into the root zone, so plants will grow bigger, healthier roots as they search for nutrients.
If you have enough space, you could run an annual trench rotation in the fall, digging and filling one trench and planting green manure or a winter crop over the top of the last one. For smaller gardens, “dig and drop” holes can work well, but don’t forget where you put them!
Worm Composting
Worm composting is a very quick way to compost because you’ll get some help with the process. It’s also a good way to compost indoors, in the mudroom or in the garage, or on a balcony, because the speed of the process stops it from being smelly.
You can buy a commercial vermicomposting setup, or you can make your own. It’s quite easy to do. Then you’ll just need to buy some red wigglers— technically, Eisenia fetida or Eisenia Andrei. Red wigglers thrive at indoor temperatures and eat and reproduce more quickly than regular earthworms. If you have friends who are organic gardeners, they may be able to give you a starter pack; you can even buy your wigglers on the internet.
Humanure—A Leap Too Far?
Some gardeners are now looking at a resource that is usually wasted: human manure, or humanure for short. We don’t just waste it, we spend vast amounts of money cleaning it up, and we risk contaminating our drinking water. So why not use it in the garden?
In some areas of the world, that’s normal. In the Himalayas, in the high-altitude desert of Ladakh, every house has a long drop toilet—a hole in the top floor of the house going to an earthbox underneath. After a year’s composting, the waste is carted out to the fields and used to fertilize the terraces.
It’s becoming normal at festivals now, too. Many French music festivals and campsites use composting toilets, and even the Glastonbury Festival has moved from chemical ‘portaloos’ to compost toilets. Natural Event, a company that runs festival composting toilets, has the memorable slogan, “Changing the world from the bottom up.”
DIY worm composting bin
To make a DIY bin, you’ll need three five-gallon buckets. One stays just the way it is; the other two need to have holes drilled in them. Drill 3/16” holes about an inch apart in the bottoms, and drill 1/8” holes around the top of each of the ‘holey’ buckets and in the bucket lid to provide aeration.
Stack one of the ‘holey’ buckets inside the intact one. Add 3-4” of shredded cardboard or paper and a few food scraps, then add the wigglers and put the lid on the bin. Add a handful of food scraps every so often. Don’t add too much; it’s best to wait till the last handful has been almost completely digested.
Once the red wigglers have done quite a bit of work in the bottom bucket, stack the next ‘holey’ bucket inside. Add fresh bedding and a handful or two of food. Once the worms are finished with the bottom layer, they’ll migrate up into the top bucket through the little holes that you drilled (their eagerness to migrate is another reason you want wigglers, not earthworms). Then you can simply slip the bottom bucket out, tip the compost on the garden, wash the bucket out, and use it as the top bucket for the next load of compost.
Don’t let the compost dry out, as that will kill the worms. Try not to drown them, either—the compost should just be spongy and damp.
Worms love fruit peelings (but not citrus), coffee grounds, tea bags, leftover pasta, melon rinds, vegetable peelings, leftover salad, and even bread. Try to avoid onions, garlic, and potatoes, and don’t give them meat, dairy, or fats.
The liquid that ends up in the bottom bucket is sometimes called ‘vermicompost tea.’ It’s great for use as fertilizer—simply water the garden with it.
By the way, earthworms do a similar job when they push up their worm castings in your lawn. If you want a quick way to help your garden out with some extra humus, just pick up the worm castings and crumble them over the soil. Your lawn looks nicer, and the rest of the garden gets the benefit!
And as a festival-goer, I can tell you, the compost toilets are a definite improvement on the old-style ones. They smell of sawdust, the floor doesn’t get wet, and they don’t need a poo tanker to empty them. Even better, instead of tipping chemicals into the sewage system, the compost toilets feed a big composter and create literally tons of compost.
If you want to use composting toilets at home, you can purchase composting toilets and even systems (which flush to a big compost tank and cost about $3,000). You can also DIY. You’ll need a big, strong container to use as your receptacle, and a seat to put over it. You’ll then want to select your composting material; you can use dry earth, rice hulls, coco fiber, sawdust, or wood shavings. When the bucket is two-thirds full, it’s time to tip it out (some people prefer to use tough biodegradable bags which they can tie up before taking to the compost heap). Always put humanure right in the middle of your compost pile, so that it gets hot and decomposes fast (and if you do this, don’t turn the pile). hen leave it for at least a year.
If you’re using humanure, make sure you don’t put your pile near a watercourse or in a boggy area. And though the humanure should be completely safe, it’s probably best to use it only on fruit trees, berry bushes, and flowers you’re not going to eat.
