Recently I’ve become slightly obsessed with saving all sorts of everyday waste – , cardboard, brown paper, wool packaging, jam jars, yoghurt pots and ready meal trays and finding ways to employ them in my small Cheshire garden.
My latest target is spent coffee grounds. I have a strong coffee most mornings, so from my one-cup cafetière, I make a large jug of soggy spent grounds every fortnight. But what can I do with them? The internet is awash with tips, but they’re hugely conflicting. However, all the reliable sources agree – they’re best incorporated into our Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.
Why are coffee grounds good for plants?
Spent coffee grounds contain a mix of organic compounds, including many of the ones that make up plants. They also contain To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key nutrients usually taken up from the soil are nitrogen, phosphorus and potassium. Plants also need carbon, oxygen and hydrogen to make carbohydrates — their main energy source. Carbon and oxygen come from the air as carbon dioxide, while hydrogen is drawn from water absorbed by the roots. Other important soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough of these nutrients to support healthy plant growth.
This describes how acid or alkaline soil is, and is expressed as a number between 0 and 14. Soil with a pH of 7 is neutral, an acid soil has a lower value, and an alkaline soil has a higher one. Most plants grow best in soil that’s within a specific pH range, so it’s useful to know your soil’s pH. Testing kits are easy to use and widely available in garden centres and online.
However, being coffee, they contain caffeine too. Most of this has been mostly washed out (I drank it!), but any left behind can reduce plant growth. Caffeine can have toxic effects on plants, inhibiting their development by suppressing root and shoot growth. However, its impact varies depending on the concentration and the species of plant, as well as lots of environmental factors like temperature.
How to use coffee grounds in the garden
How quickly coffee grounds Decompose means to break down or decay into simpler substances. In gardening, it often refers to the process of organic matter breaking down when added to compost or soil. This process is important for creating healthy soil and providing nutrients for plants.
What kind of plants can you put coffee grounds on?
Last year, as well as adding grounds to my compost heap, I decided to proceed very gingerly and see if just a little bit of extra slight acidity around some of my plants helped them. Perhaps it could be just enough to coax a few reluctant specimens into flowering. With a very sparing amount raked carefully in around the base of any acid-loving plants, this gentle approach seems to have worked well in my garden. My azaleas were incredible last year, and even a very stubborn and temperamental creamy white camellia in a large pot flowered well after this approach. Hurrah!
A word of caution though: avoid applying lots of coffee grounds in thick layers, as this could be far too much for some plants, and can also create a barrier that prevents water and air from reaching plant roots.
How we use coffee grounds at RHS Bridgewater
We’ve established that coffee grounds used in the right way can benefit plants. So at RHS Bridgewater, where I’m based, all the coffee grounds from the onsite catering are recycled for gardening. The catering team fill up big used mayonnaise tubs with the spent grounds, and the Curatorial team from the Kitchen Garden collect them while dropping off supplies of fruit and vegetables, or when passing the Welcome Building on the tractor. The grounds are then added to the compost bays – a win-win for sustainability.
But we like to share too, and visitors can also grab a bag of free used coffee grounds from a new self-service point to take home for their own gardens.
Previously, the coffee grounds were part of the food waste collected by an external contractor, so were still recycled, but this involved vehicles, fossil fuels and further processing. Now that the grounds are collected and used on site or offered to visitors, this frees up waste space. It might not sound like a big deal, but busy weeks at the Garden can see over 5500 cups of coffee sold, with the catering teams working their way through over 120kg of coffee grounds. This adds up to about a tonne of grounds every other month!
I hope this has inspired you to try using coffee grounds in your own garden – and look out for the collection point next time you visit RHS Bridgewater.
