How To Use Coffee Grounds In the Garden
Coffee shops often give coffee grounds away free to gardeners, as they’re a waste product they would
normally have to pay to dispose of. For coffee-loving gardeners, this freely available resource
sounds like a real boon.
Coffee grounds contain several key minerals for plant growth — nitrogen, calcium, potassium, iron,
phosphorus, magnesium and chromium.
They may help absorb heavy metals that can contaminate soil.
What’s more, coffee grounds help attract worms, which are great for your garden.
Here are 4 ways to use coffee grounds in your garden.
Coffee beans contain caffeine, which is said to suppress the growth of
other plants to reduce competition for space, nutrients, water and sunlight. How much caffeine actually
remains in used coffee grounds is debatable, and some plants will be more sensitive to caffeine than
others. It would be sensible to avoid spreading coffee grounds around seeds or seedlings as they may
inhibit germination and growth.
Coffee grounds alone for mulching could be detrimental. Like
clay soil, coffee grounds consist of very fine particles that are prone to locking together. This turns them
into a barrier that will resist water penetration and eventually result in plants dying of thirst.
The solution is to mix coffee grounds with other organic matter such as compost or leaf mold before
using it as a mulch. Alternatively, rake your coffee grounds into the top layer of soil so that they can’t
clump together. Variable particle size is key to good soil structure.
Coffee grounds are often said to be acidic but this can vary a lot, from very acidic to slightly alkaline, so
don’t expect them to acidify higher pH soils.
Coffee grounds contain a good amount of the essential nutrient nitrogen as well as some potassium and
phosphorus, plus other micronutrients. The quantity and proportions of these nutrients varies, but coffee
grounds can be used as a slow-release fertilizer.
To use coffee grounds as a fertilizer sprinkle them thinly onto your soil, or add them to your compost
heap. Despite their color, for the purposes of composting they’re a ‘green,' or nitrogen-rich organic
material. Make sure to balance them with enough ‘browns’ – carbon-rich materials such as dried leaves,
woody pruning or newspaper. Your compost heap’s tiny munchers and gnawers will process and mix
them effectively, so using coffee grounds in this way is widely accepted to be safe and beneficial.
Many vermicomposters say that their worms love coffee grounds, so small quantities could also
regularly be added to a worm bin if you have one. Paper coffee filters can go in too.
An oft-repeated nugget of advice is to spread used coffee grounds around plants that are vulnerable to
slug damage. There are two theories why: either the texture of the grounds is abrasive, and soft-bodied
slugs prefer not to cross them, or the caffeine is harmful to slugs so they tend to avoid it.
However in an experiment slugs took just seconds to decide to cross a barrier of coffee grounds! The
same researcher also sought to find out if coffee grounds would repel ants, with similar results – ants
may not particularly like coffee grounds, but they won’t scarper out of your garden to get away from
Composting with coffee is a great way to make use of something that would otherwise end up taking up
space in a landfill. Composting coffee grounds helps to add nitrogen to your compost pile.
Composting coffee grounds is as easy as throwing the used coffee grounds onto your compost pile.
Used coffee filters can be composted as well.
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