Using spent coffee grounds is one more way for us to turn so-called waste into a useful and valuable resource around the home.
An average cafe collects around 320 kilograms of coffee grounds each month and if it gets put into landfill, where it breaks down anaerobically, it converts to harmful greenhouse gases.
In The Garden
Spent coffee grounds contain a whole range of useful things for gardeners, like nitrogen, potassium, calcium and trace minerals. While coffee grounds can be sprinkled sparingly – no more than one handful per square metre – straight onto the garden, they can be acidic, so you’re better off adding them to your compost or your worm farm to break down and neutralise the acid. If you do opt to use them directly on your garden, aim to use them around acid-loving plants like blueberries, and steer clear of any seedlings, where research has shown it can stunt young plants’ growth, and a light application is key. If you’re unsure, observe any impacts it has on your beds by performing a soil test.
Many people have successfully cultivated mushrooms in spent coffee grounds. And because of the temperature of the water used in coffee machines, there’s no need to sterilise the substrate before mixing through your mycelium.
Compost And Worm Farms
Spent coffee grounds contain about two percent nitrogen (roughly the same amount of nitrogen as grass clippings) and make a great addition to your compost. Despite their colour, coffee grounds are used as a green – nitrogen – component in the compost, so make sure to balance them with enough brown – carbon – when adding it in large quantities, like what you might collect from your local cafe.
Coffee grounds can be given to worm farms, too. Worms will eat through them quickly and the moisture content often found in spent coffee grounds helps prevent the worm farm from drying out.
Around The Home
There are lots of uses for spent coffee grounds around the home. From skincare (Pip, Issue 15) and cleaning products, through to natural dyes and neutralising odours in the chook pen. Coffee can be used as a rubefacient, which means it stimulates local blood flow when applied to the skin. It’s coarse in texture, making it a great moisturising hand exfoliant for gardeners (see breakout).
Spent grounds can also be used as an abrasive agent
to help scrub any item you otherwise might use steel wool on. But because coffee can stain, it’s best to stick to cast-iron or stainless-steel surfaces that won’t absorb the colour. But that’s why it makes a good natural dye option – try starting with a light-coloured ball of wool and experiment with different amounts to achieve different intensities of brown pigments.
There are plenty of recipes where fresh coffee can be replaced with spent grounds to achieve an equally successful result. And while experience has shown that chooks won’t particularly like to eat spent grounds, coffee is a good addition to any kind of poultry pen as a way to neutralise odours.
Gardener’s hand scrub
1 cup spent coffee grounds
1/3 cup of coarse or rock salt
2 drops essential oil
Combine coffee and salt before mixing in the essential oil. Add one tablespoon of the scrub to your hands and rub over the skin to exfoliate the hands and leave them soft and smooth. Store in a jar for up to three months.