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Why you should be using coffee grounds in the garden

22nd April 2021

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Coffee and gardening. Unless you’re drinking a cup in the potting shed it’s an unusual combination, but the link goes much further than that. If you’re a coffee enthusiast with green fingers, then your beverage of choice could also be a fantastic asset to your garden.

Used coffee grounds (leftover from using a cafetiere, filter or industrial coffee machine) contain a substantial amount of nitrogen, as well as potassium and phosphorus. These properties make them perfect for garden activities such as composting. It’s an innovative way to make use of something that would’ve otherwise ended up in a landfill.

To help give your garden a fresh boost, coffee expert Lewis Spencer of has revealed how to safely use coffee grounds in your garden.

1. Slow-release fertiliser
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.

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. Feed your worms
If you practice vermicomposting 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.

3. Deter slugs and snails
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.

4. Add 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. (Our 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’ve 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.

5. Mulch
Mulch is helpful in reducing weed growth and keeping soil moist. 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. 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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