Coffee is the most popular drink worldwide, with around two billion cups consumed every day, according to the British Coffee Association. Even accounting for a proportion being instant coffee, that still results in a huge amount of coffee grounds – the term for the waste left over from a coffee percolator or filter. Like most organic kitchen waste, coffee grounds are great to recycle in the garden to benefit your soil and your plants and this is far better for the environment than adding it to household bins or pouring it down the drain where it could cause blockages.
Coffee grounds have been the subject of a huge amount of anecdotal advice with mixed results for a wide variety of uses – as a slug, pest, and animal deterrent, as a mulch, and as a fertilizer. But, because of the great variability of coffee grounds due to the type, content, and method of brewing, there has been no definitive scientific research on the use of coffee grounds. Here we advise on how best to use coffee grounds in your garden.
Are coffee grounds good for plants?
Coffee grounds are an excellent compost ingredient and are fine to apply directly onto the soil around most garden plants if used with care and moderation. Coffee grounds contain nutrients that plants use for growth. The grounds are relatively high in nitrogen and also contain potassium and phosphorus, as well as being a source of moist organic matter.
How do you use coffee grounds for plants?
The safest way to use coffee grounds in the garden is to add them to compost containers or worm bins. Used grounds compost well, and home-made compost is superb for improving soil and growing healthy plants. While applying coffee grounds directly onto the soil around most plants is usually fine, this should be done with care as using grounds in this way is never a one-method-fits-all approach. The chief potential problem is that if applied in quantity to the soil surface, the fine particles clog together to form a barrier that prevents water and air from reaching plant roots.
Simply emptying your coffee pot onto the border soil of established plants is fine as long as it’s not in the same place time after time. If you notice the grounds starting to build up, just rake or turn over the soil surface to incorporate the grounds into the top several centimetres of soil.
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Composting used coffee
The moist, small particles of coffee grounds are certainly an excellent compost ingredient because of their texture, to mix with dry and woody waste to speed the composting process. Ensuring a balanced mix of ‘wet’ and ‘dry’ materials is the best way to achieve good compost. The nutrients contained in coffee grounds will be recycled back onto the soil when finished compost is used as a mulch or dug into the soil. Also add any un-drunk coffee to dry material in a compost bin.
Which plants benefit from used coffee grounds?
Coffee tends to be slightly acidic and is therefore good for acid-loving plants such as hydrangeas, as well as nutrient-hungry plants like roses.
Coffee grounds are one of many materials said to repel slugs and can be used around favourite slug plants such as hostas, though results are not guaranteed.
Which plants do not like used coffee grounds?
Coffee grounds are likely to contain some caffeine unless it is decaffeinated coffee. Whilst most of the caffeine in coffee is transferred to the drink in the brewing process, some may remain. Caffeine restricts the growth of certain plants, notably tomatoes, and may inhibit germination of seedlings.
What will coffee grounds repel?
The favourite use of coffee grounds as a pest repellent is against slugs, which are said to dislike the caffeine in coffee and the gritty texture of the grounds. Some gardeners have had good results with using coffee as a slug deterrent while others report that it has no effect. Other gardeners use coffee as a repellent for ants, cats, and foxes, again with varying results. As with any organic repellent, frequent application is needed and especially after rain.
Coffee grounds and dogs
Note that the caffeine in coffee can be toxic to dogs. Whilst grounds that have been brewed usually contain very little caffeine, if your dog tends to eat anything going, don’t spread grounds on the soil surface but instead add to the compost bin or bury in the soil.
Where to get coffee grounds for your garden?
As well as your own kitchen, and friends who do not have gardens, there are coffee shops, cafes and restaurants that sometimes put out tubs or bags of used coffee grounds to take away for free. If not, it’s worth asking.