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This Week’s Guest Blogger is Evie Somers Lead Editor at Up Gardener

“Can I use coffee grounds in the garden?” is a common question. The answer? “It depends!” Here’s what you need to know about composting with coffee grounds

For many of us, a cup of coffee is an integral part of the morning routine. If you’re someone who enjoys making their brew from grounds rather than instant, then this post is for you. We’re going to teach you how to use coffee grounds for composting, and the benefits they’ll deliver.

Why use coffee grounds in the garden?

There are a few good reasons to use coffee grounds in your garden, which we’ll introduce below.

Reason 1: Sustainability

This one is simple: Coffee grounds can be used in the garden, so surely it’s better to do so than to throw them in the bin. Whether or not you’re a strictly organic gardener, reward yourself with the warm fuzzy glow of doing something small for the environment.

Reason 2: Nutrients

Coffee grounds are rich in essential nutrients, especially nitrogen. One of the main functions of compost is to nourish your plants and encourage growth, but not all compost is suitable for all situations. If you’re growing plants that need nitrogen-rich soil, compost containing coffee grounds will be helpful.

When composting, a general rule of thumb is to add ‘brown’ and ‘green’ ingredients, in a ratio of about 4:1. Brown ingredients provide carbon and help air to circulate in the compost pile, while green ingredients provide other nutrients, including nitrogen. While coffee grounds are brown in colour, they’re considered green compost ingredients. Chuck them in your pile along with other green ingredients like fruit and veg scraps, and brown ingredients like straw, newspaper, dried leaves and more, and your pile will start to develop nicely.

Reason 3: Versatility

If you’re not an enthusiastic composter, you may not know that there are several common composting systems. Coffee grounds can be used in all of them –

  • Cold composting: This is the most common, sling-it-all-in-a-pile method. The compost bins you see at the end of people’s gardens contain cold compost. You just chuck stuff in and leave nature to take its gradual course.
  • Hot composting: In hot composting, you mix the pile regularly to encourage aerobic breakdown. When done properly, the inside of a hot compost pile can get up to 70 degrees Celsius! At this temperature things break down a lot quicker.

Circulating compost speeds up the whole process!

  • Bokashi: Technically this is a fermentation process rather than a composting one, but many gardeners lump them together. Bokashi uses bran to provide enzymes that ferment all sorts of food, and coffee grounds can be used alongside or as an alternative to this bran.
  • Vermicomposting: ‘Vermi’ is the Latin root for ‘worm’, and in this method, worms play an active role in composting by processing whatever scraps you give them. Worms can’t tolerate many coffee grounds, so go easy.

A few caveats

You’ll notice we’ve focussed heavily on compost so far. Here’s why: Uncomposted coffee grounds can actually cause harm in your garden!

You may hear people recommend using coffee grounds directly, either by working them through the soil, or applying them as a top layer of mulch. Despite being fairly common advice, this should be avoided. Uncomposted grounds still have a high caffeine content, and caffeine has an allelopathic effect on some plants.

What does allelopathic mean?

Allelopathy is a process through which one plant inhibits growth in another plant. You hear about plants competing for sunlight, with the loser not getting the nutrients it needs to photosynthesise enough. Well, caffeine can have a similar impact. Some plants produce caffeine as a means of gaining a natural advantage over surrounding plants by stifling their growth. With this in mind, adding raw coffee grounds seems like less of a good idea!

How not to do it

What about using coffee grounds as mulch?

Maybe you’re wondering whether you can use coffee grounds as mulch for plants that you’re sure won’t be negatively affected by caffeine. Again, we’d advise not.

The reason here is that good mulch needs to have certain properties: It needs to keep moisture in the soil below, while also allowing air and new moisture in. Unfortunately the texture of coffee grounds leads them to compact into a layer that’s too dense to let enough air and water through.

Chuck them in the compost pile, though, and they’ll become part of a mixture that lends itself well to use around the garden!

Coffee and compost

There you have it: Three reasons why you should be using coffee in your compost, along with a couple of caveats to avoid common pitfalls.

Thanks for reading. It’s our hope that you’re now inspired to save your coffee grounds from the rubbish bin, and divert them to your compost pile instead. Whichever your preferred means of composting, coffee will make a fine addition


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