Good compost grows healthy plants, and you can never have too much of it! Homemade compost is ideal if you can make it – here are a few tips from Wellington blogger, baker and gardener Elien Lewis, selected from her new book Homegrown Happiness.
Photography: Elien Lewis
Homemade compost is the best thing for your garden. That sounds like a bold statement, but it’s true. Whether it’s compost in a bin, or you’re directly letting plants and organic matter decompose in your garden, it’s all about creating a nutrient-rich layer for the soil. A good quality compost only needs to be applied once or twice a year, and it will supply your soil and plants with the nutrients they need without the need for any added fertilisers.
Composting at home can seem daunting. There are many books on composting methods that require precise layers, temperatures and amounts. In reality, nature is creating compost non-stop without being exact about it, so it doesn’t need to be that precise. A compost pile can give clear signs when something is lacking and, once you recognise these signs, it’s easy to make the necessary tweaks.
I want to cover a few different composting options, because there is one for each and every home and section, no matter where you live. As well as feeding your garden, any organic material that you can save from landfill is a bonus. [Elien’s book also covers worm farming and bokashi – Ed.]
Composting is how nature recycles organic materials. That includes all plant and animal matter. Composting is an aerobic decomposition method, which means it needs air and relies on aerobic organisms to break material down.
A compost pile needs four things to work efficiently:
- Carbon – the carbon component is made up of dry materials such as brown leaves, twigs, cardboard, straw and hay. It’s what gives the soil organisms the energy to work hard. The soil organisms oxidise the carbon, which generates heat in the pile. The carbon component of the compost pile is known colloquially as the ‘browns’.
- Nitrogen – the nitrogen component is made of fresh organic material. This includes all fresh plant and food scraps, coffee grounds, fresh seaweed and grass clippings. Nitrogen encourages the organisms to reproduce. The nitrogen component is known colloquially as the ‘greens’.
- Oxygen – this is a necessary component for the carbon to oxidise and is crucial for aerobic organism survival.
- Water – this is needed in small amounts to assist the aerobic organisms with decomposition.
A very rough ratio I follow for my compost is one part green to two parts brown, though I don’t get hung up on working out the exact amounts. If the balance is wrong, my compost pile will let me know.
The exact ratio of carbon to nitrogen required for a well-balanced compost pile is a hot topic among gardeners. You may read about 25:1, 30:1 or even 50:1 carbon to nitrogen. Don’t worry – this doesn’t mean 50 parts of browns to one part greens. All organic material contains carbon, even the fresh green stuff, so a ratio of 50:1 is talking about the carbon from all the material in the heap, not just the browns.
Making a compost pile
A simple compost pile is easy to make. It can be made as a pile directly on the ground or in a designated compost bin. It involves layering the ingredients like a messy lasagne, alternating between browns and greens. Perfect, separate layers are not the goal here. They need to be a bit mixed. Once you’ve added in all the ingredients, give it a stir to help combine it.
The brown component is responsible for adding carbon but also capturing air in the pile as twigs and leaves can create little air pockets. The fresh greens add nitrogen and water to the pile. Sometimes a little extra water can be added to the brown layers. A compost pile should be damp but not soaked.
Finishing with a layer of browns on top hides the rapidly decomposing greens, which can create bad smells or attract flies.
A compost heap like this can just sit and do its thing, and you can tip more organic material on top as you have it. Giving it a turn every few weeks will speed up the decomposition as, with each turn, you’re adding in more oxygen. For this, I love my steel compost-turning stick. It’s like a giant screw. I simply stick it into the pile and turn it, so it screws itself into the heap, then I pull it up and knock off what has been pulled up. It turns the pile without any hard work.
A compost pile like this won’t get very hot (though turning it will generate more heat), so it can take between six months and a year to create usable compost. The bottom layer will be ready to use first. Once it’s dark brown, crumbly and sweet smelling, it is ready to use.
How to tell if something’s wrong
A well-balanced compost pile shouldn’t be smelly. When it’s turned, you should notice lots of worms, a bit of heat and signs it is actively breaking down.
Smells like ammonia
This is a sign that there is too much nitrogen in the pile. The organisms in the compost pile release the excess nitrogen in the form of ammonia.
A simple fix for this is to add more carbon-rich material, through a helping of browns. Stirring through a layer of ripped-up cardboard, shredded leaves or straw will help.
Slimy and smells of rotten eggs
This is a sign of a compacted or overly wet compost pile. Both can result in a pile that lacks oxygen. When there is not enough oxygen, the aerobic bacteria die, and the anaerobic ones take over. These bacteria, which survive without oxygen, are responsible for that rotting sulphur smell.
Turn the compost to bring more air into the pile. Adding in different sized browns also helps as they create air pockets in the pile and soak up the excess moisture.
Stagnant and doing absolutely nothing
This is a sign of too much carbon and not enough nitrogen. Nitrogen feeds and helps reproduce more soil organisms. Without enough nitrogen, there won’t be enough organisms to break down the excess carbon.
This can be remedied by adding more fresh greens, but they’ll need to be mixed deep into the pile. A compost turner can help do this. Fresh grass clippings or manure can add the needed nitrogen.
Compost bin do’s and don’ts
Disease-free plant materials
Vegetable and fruit scraps
Horse, cow, sheep, rabbit, guinea pig or chicken manure
Cardboard and paper
Untreated sawdust or wood shavings
Straw and hay
Home compostable packaging
Dog and cat waste
Plastic-coated paper or cardboard
Treated wood sawdust or shavings
Cooked food scraps
Meat or fish
In situ means ‘on-site’ and it involves letting organic waste break down either directly on the soil surface or dug into pits and trenches.
This method is very easy and fuss-free and, as the aim isn’t to create a working compost heap, there’s no emphasis on layers or the correct carbon and nitrogen amounts.
Disease-free green waste such as the leaves and stems of spent plants can be chopped up and laid down right where they are. This is known as a chop-and-drop technique. They’ll provide a mulch and, once they break down, they’ll feed the soil life.
Trench composting – also known as pit composting – is a great way to dispose of organic material that you can’t put in your above-ground compost bin or on the soil surface. Cooked foods and fish scraps, for example, do well being dug into the ground. This is really an underground worm farm, so this type of compost relies on a lot of worm activity to break down and excrete the organic matter in the trench or pit.
It does require digging, though, so I avoid doing this in my actual vegetable gardens.
I do my trench composting around fruit trees or in places that I have yet to transform into no-dig patches.
Simply dig a long trench or pit, at least 50–60 centimetres deep. Place your organic matter in it, then cover with soil and it’s done!
If dogs and cats digging up the compost is an issue, lay a few rocks or untreated wood planks over the covered hole.
This gorgeous and practical gardening book covers all the basics of establishing and planting a no-dig organic edible garden, with month-by-month gardening tasks and delicious seasonal recipes.
Homegrown Happiness: A Kiwi guide to living off the suburban land, by Elien Lewis, photography and recipes by Elien Lewis, published by Bateman Books, $39.99, available now at all good bookshops and batemanbooks.co.nz.