For those of us trying to live a more sustainable lifestyle, the idea of finding a use for items we’d normally throw away can be exciting. Anything that can be saved from landfill is a ‘win’, and so we hit the search engines for innovative ideas of how to reuse our waste.
For the coffee drinkers out there, used coffee grounds can be a problem. Finding ethical coffee brands has become a lot easier in recent years, but regardless of how careful you are in sourcing your daily caffeine hit, the coffee grounds all tend to end up in the same place – the bin!
Could there be a solution?
Using coffee grounds for gardening is becoming increasingly popular. A quick online search gives you lots of results, all raving about the many benefits used coffee ground can provide for your outside space.
However, caution is needed, and you need to be very careful that you’re not doing more harm than good.
As keen coffee drinkers and sometimes keen gardeners, we wanted to find out exactly how we should be using coffee grounds in our garden. Read on to find out what we discovered!
Composting with Coffee Grounds
A common and straightforward suggestion for used coffee grounds is to add them directly to your compost. Despite being brown in colour, coffee grounds are classed as a ‘green’ as they are rich in nitrogen. You, therefore, need to balance out their addition with extra ‘brown’ materials such as brown leaves, paper or straw.
Before you go skipping up the garden with your used coffee grounds, we do have some words of caution.
A study carried out in 2011 looked at three methods of composting used coffee grounds from the restaurant and coffee shop industries. While they found that coffee was highly compostable, they also reported that the mortality rate of earthworms increased in all three composting methods tested. However, they found that adding cardboard was a good way of reducing our wiggly little friends’ mortality rate as it reduced their exposure to the organic compounds released by the decaying coffee grounds.
If you do want to start adding coffee ground to your compost, do so sparingly and ensure you’re adding plenty of ‘brown’ materials to compensate.
Coffee Grounds as Fertiliser
Another option of using your coffee ground for gardening is as a fertiliser. Coffee grounds contain nutrients such as Nitrogen, Potassium and Phosphorus, plus several other micronutrients that can benefit plants.
To fertilise your plants with coffee grounds, simply sprinkle a thin layer around the base of your plants and then lightly work them into the soil. Be careful not to use too much in any one area as the grounds can clump together and reduce the soil’s ability to absorb water.
Many resources suggest that adding coffee to your soil will lower the pH levels (or raise the acidity levels), benefitting plants that thrive in more acidic soils. However, this is only true of unwashed coffee grounds. Rinsed grounds have a near-neutral pH of 6.5 and won’t affect the acidity of the soil.
Feeding Roses Coffee Grounds
Roses, Camellias and Hydrangeas are all nitrogen loving plants that benefit from the nutrients coffee grounds can provide.
Feeding your roses with coffee grounds in springtime will give them a much-needed nitrogen boost to support new growth and help them stay healthy and disease-free.
However, caution is needed as sprinkling coffee grounds too closely to your roses can cause nitrogen burns, which can kill the rose in the worst instances.
To avoid this, simply drop a small handful of grounds into a watering can and leave them for a couple of days. This will create a lovely amber coloured liquid that can be used to feed your roses and other nutrient loving plants. Mixing the grounds with water removes the issue of nitrogen burn and helps the nutrients found in coffee grounds to reach the plant’s roots.
Using Coffee Grounds as Mulch
A popular method of using your coffee grounds for gardening is to use them for mulching. Mulches are typically loose coverings of materials such as bark or straw placed on the soil’s surface. Mulching has many benefits, including saving water and suppressing weeds. It can also give a garden a tidy appearance.
Using your coffee grounds for mulching seems like an excellent solution for both your garden and reducing what you send to landfill. However, you need to take care, or you could do more harm than good.
Some gardeners have reported calamitous results from mulching with coffee grounds. These results seem to stem from overusing coffee grounds and applying a thick layer around plants and over seedlings. This approach could lead to two issues.
The caffeine in coffee beans has been shown to suppress other plants’ growth, so the coffee plant has less competition for sunlight, water, and nutrients. Although the amount of caffeine remaining in coffee grounds is relatively low, and not all plants are affected by caffeine, it is best to avoid using your grounds around seeds or seedlings as it could limit growth.
As we mentioned when discussing using coffee grounds as fertiliser, the used grounds can bind together. If a thick layer of grounds is applied on top of the soil, they could create an impenetrable barrier that will stop water from getting through, with the result that the plants die of thirst.
The answer is to mix your coffee grounds with other organic materials such as leafmould or compost before using it as a mulch. This will ensure that the grounds don’t clump together, but your garden still benefits from the nutrients the coffee grounds will provide.
Coffee Grounds and Garden Pest Control
Many gardeners use coffee grounds as a form of natural pest control, spreading them around plants that slugs want to make a meal of. The grounds are meant to form a rough, abrasive barrier that the slugs won’t want to cross. There is also a theory that caffeine is harmful to slugs, and so they will steer clear of coffee grounds and leave your precious plants alone.
A study into the effectiveness of using coffee grounds as a slug repellent was far from promising. Unfortunately, the slugs crossed the grounds after only a few seconds.
Caffeine, in large doses, is toxic to slugs and snails; however, it may be that used coffee grounds don’t contain enough caffeine to be an effective repellent.
Using Coffee Grounds for Gardening Summary
Coffee grounds can be used in the garden to great effect, providing you do so sparingly. Some plants such as Roses will love the nutrients they provide, but overuse can lead to gardening woes. If you’re a big coffee drinker, then it’s unlikely you’ll be able to use all your grounds in your garden. However, even saving a small proportion from going to landfill is still a good result.