By Lucy Searle
Did you know that used coffee grounds can be put to work in the garden to improve conditions and produce better results?
This unusual yet effective combination is the perfect pairing – using leftover coffee grounds from your coffee maker is the perfect way to cut down on waste and to garden sustainably.
Used coffee grounds contain a substantial amount of nitrogen, as well as potassium and phosphorus. These properties make them perfect for composting.
Here, coffee expert Lewis Spencer of Coffee Direct reveals how to safely – and effectively – use coffee grounds in your garden.
1. Use coffee grounds in the garden as a slow-release fertilizer
Coffee grounds have a varied amount of essential nutrients in each batch, but they all contain nitrogen, potassium and phosphorus alongside micronutrients.
Plants such as carrots, azaleas and roses would appreciate a nice boost from coffee grounds. However, tomatoes do not like the grounds.
See: Tomato companion planting – the best crops to grow with tomatoes
To use coffee compost, simply sprinkle the grounds directly onto your soil and lightly rake it in. Coffee grounds add organic material to the soil, helping water retention, aeration and drainage. Leftover diluted coffee can create a liquid plant fertiliser too. Simply mix two cups of brewed coffee grounds with five gallons of water in a bucket overnight.
2. Use coffee grounds in the garden to feed worms
If you practise vermi-composting with a worm bin, coffee grounds are a must as worms love them.
For a small bin, add a cup of grounds per week to feed their addiction. Avoid adding too much at once because the acidity could negatively impact your worms. Paper coffee filters can even go in too.
See: Rewilding – 10 ways to rewild your garden
3. Deter slugs and snails with coffee grounds
Coffee grounds are a great repellent for slugs and snails. Simply spread the grounds around vulnerable plants to create a barrier against the insects.
Research shows that caffeine is effective in repelling slugs and snails when applied to foliage or the growing medium of plants. This is because of the naturally abrasive properties of coffee: soft critters tend to avoid rough surfaces.
- You can even use coffee ground for vegetable beds. See, Raised bed garden ideas – for productive, low-maintenance gardening
4. Add coffee grounds to compost
Good compost contains a mixture of ‘brown’ and ‘green’ ingredients. Brown materials such as dried leaves, sawdust and newspaper bring carbon to the mix. Green materials such as tea leaves and grass clippings offer nitrogen and protein. (The rule of thumb is to have a 4:1 ratio of brown to green compost material.)
Compost is a great way to make use of something that would have ended up in landfill. Coffee grounds, paper filter included, fall into the green category which means they are rich in nitrogen at approximately 1.45%.
They also contain magnesium, potassium and other trace minerals.
See: Monty Don's warning about compost – heed his advice or risk attracting rats
5. Use coffee grounds in the garden as mulch
Mulch is helpful in reducing weed growth and keeping soil moist. It’s notoriously difficult to come by compost or straw in large quantities at a low price.
Coffee grounds work best as mulch when mixed with other organic matter such as leaf mould. The combination will reduce the risk of clumps forming which can become a barrier to water and suppress the growth of your plants.
See: Monty Don's tips on mulching – and what to do now
As plants could be sensitive to the caffeine in the grounds, avoid creating a thick layer. Using a mix of particle sizes will promote good structure
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