One of the hot topics in permaculture and organic gardening at the moment is biochar, an idea that is being developed after the discovery of charcoal-rich dark soils in the Amazon region (also known as Terra preta), which date back to before the arrival of the Conquistadors. These dark soils are surprisingly rich, even now, holding onto nutrients and improving soil fertility.
The modern take on this is that we could solve several problems with biochar. Firstly, we could turn crop wastes and other waste organic matter into biochar, which helps with waste disposal. Producing biochar emits less carbon dioxide than open burning, and the remaining carbon is locked in the biochar – which then acts as a carbon ‘sink’ if buried in the soil. Biochar could allow us to lock away excess carbon for centuries, helping to avoid the worst effects of global warming.
And once it’s in the soil the biochar will prevent nutrient leaching and improve soil fertility, helping to produce more crops from less land and fewer fertilizers or other inputs.
If it sounds too good to be true, then that’s because it might be. Some research is being done on the best ways to produce biochar, and the effects it has once it has been buried in different soils or is used in different climates. It does look as though small-scale biochar production can improve soil fertility; whether we can scale up production and create a useful carbon sink is a different matter.
Biochar is really just charcoal – the result of organic matter being burned slowly with a restricted oxygen supply (pyrolysis) – that has been made to be used as a soil improver rather than as a fuel. It is possible to make charcoal on a small scale, and small charcoal kilns are available. You could produce your own supply of BBQ charcoal, artists charcoal and biochar if you have suitable waste products available.
It’s probably not a good idea to dig commercial charcoal briquettes into your garden, as they may well have been treated to make them easier to light. If you have a source of locally produced, untreated charcoal then you might like to try it. You may even be able to get hold of charcoal ‘fines’, which are pieces too small to be sold as BBQ charcoal, and biochar products are becoming available.
Here in the UK it is also possible to buy GroChar compost, a ready-made (and peat-free) biochar soil improver, although there are currently limited stockists.
Oxford Biochar sell bags of biochar (1.5 kg and 10 kg) and a biochar-rich seeding compost. They have a few stockists in the south of England, but you can also order online.
Maybe you’re one of many people wondering how to reduce the amount of trash you produce. Maybe you’re wondering why your local coffee shop is giving away its waste coffee grounds to gardeners. Or maybe you want to know where to find a free source of fertility for your garden. The answer to all three questions is that coffee grounds are great for making compost and as plant food.
If you can’t function without a proper cup of coffee in the mornings, then you may well brew your own. If so then you have a ready supply of coffee grounds to use in the garden. If you’re not a coffee drinker, or you don’t have a coffee machine, then you’ll have to hunt down a local coffee shop that gives its waste grounds away – or maybe there’s a coffee machine at work you can empty.
If you’re after a low-maintenance garden, then you can simply toss your waste coffee grounds onto the soil as a mulch. Their dark color absorbs heat from the sun and can help the soil to warm up, and they’ll add nutrients to the soil as they break down.
Another advantage of using coffee ground directly on the soil is that they can deter pests. Slugs and snails aren’t fond of the caffeine or the gritty texture, and might go elsewhere for a munch. If you have a problem with cats using your garden as a litter box, then a coffee mulch can help to disguise the smell and encourage them to ‘go’ elsewhere. And if you’ve got access to a regular supply of coffee grounds, then it’s worth experimenting to see whether the smell confuses carrot flies, and other pests that find their way to your plants by smell.
Put about a pound of coffee grounds into a bucket or watering can with 5 gallons of water, leave it to warm up for a little while, and you’ve got a nitrogen-rich feed that you can use on hungry plants in your garden. The resulting feed will be slightly acidic – good for use on acid-loving plants (such as camellias, azaleas, gardenias, hydrangeas, rhododendrons, and blueberries). You can use it elsewhere, but keep an eye on your soil pH by testing your soil each season with a soil pH meter or garden chemistry test kit.
Try and use your grounds while they are fresh. Because they’re damp and full of nutrients, coffee grounds quickly start to go mouldy. Mouldy coffee grounds are still fine to compost (but it’s always best to avoid breathing in fungal spores). The carbon to nitrogen ratio of coffee grounds is around 20:1, which means that it adds a nitrogen boost to your heap that can kick-start the composting process or compensate for a lot of carbon-rich ‘brown’ materials (woody plant stems, crumpled paper or cardboard). The C to N ratio of coffee grounds is similar to that of grass clippings, and because it has been ground up it has a large surface area and breaks down quickly.
You can also add coffee grounds to your worm composter – the worms will love munching their way through them. In a worm composter, you’ll need to keep a careful eye on the pH levels to keep your worms happy. Balance out the acidic coffee grounds with some lime, or crushed up eggshells.
If you’re a real coffee addict, then you’ll also appreciate the final bonus using coffee grounds brings to your garden. Everywhere you go in your garden, you’ll get that fresh coffee aroma!