Using Coffee Grounds in your Vegetable Garden | Benefits, Myths, and Cautions

Updated: Aug 11

I like the idea of not just throwing waste out and finding some kind of use for it. In Britain, we used to be a nation of tea lovers, but now it seems we moved over to coffee.

With all that coffee leftover, wouldn't it be good if it could be cycled back into helping our vegetable garden grow?

I've found that there are lots of benefits to using coffee grounds in the garden, but there are some myths, and the need to exercise caution too.

Coffee with plants and succulents on a table

Are coffee grounds too acidic for the vegetable garden?

Unbrewed coffee grounds aren't acidic, once you've drunk your coffee, you've consumed most of the caffeine and acidity it contains, so what's left can be used in the garden.

Studies have shown that coffee grounds are slightly acidic at 6.5 - 6.8 ph. So it will be useless if you try to use it to bring down the alkalinity of your soil. But great for plants that love slightly acidic soils.

Plants that love coffee grounds

Coffee grounds are slightly acidic, but that's ok, some edible plants love this slightly acidic environment such as:

  • Carrots

  • Radishes

  • Onion

  • Tomatoes

  • Squash

  • Cucumber

  • Cabbage

  • Broccoli

  • Turnips

  • Gooseberries

  • Raspberries

  • Strawberries

  • Blueberries

Coffee grounds as a fertilizer

Coffee grounds act as a slow-release fertiliser, when used in your vegetable garden. It contains nutrients that the plants like such as:

  • Nitrogen

  • Potassium

  • Phosphorus

Whilst coffee grounds contain nitrogen, they shouldn't be used to replace a nitrogen fertilizer. The reason why is because it needs micro-organisms to break down the coffee grounds to release the nitrogen and it takes much longer.

Studies by Oregon State University have shown that lettuces grown in a potting mix that contained 25% coffee grounds, performed worse than lettuces grown without. Showing that coffee grounds weren't that effective as a nitrogen fertilizer.

Coffee grounds as Mulch

You can add coffee grounds to your vegetable garden by sprinkling some into your potting mix.

You can make it into a mulch by sprinkling it with other organic mulch that you use to mulch your garden. Make sure it is mixed with other mulch and not left to dry out on the top of your soil, otherwise it will prevent moisture from getting into your soil.

Other mulch ideas:

Visit my article here on using hay as mulch

Coffee grounds as a repellent

You'll find a bunch of articles on the net that advise you to use coffee grounds as a repellent.

However, this advice is anecdotal and hasn't proven to be 100% effective in repelling slugs and ants.

My advice is to give it a try as a natural option. It's said that slugs find the texture of the coffee grounds uncomfortable and the grounds are toxic to them. It may deter 1 or 2 slugs but not a whole host of them.

Gardenmyths attempted to use coffee grounds to deter ants and it worked for a few hours, then the ants moved the coffee out of the way, and continued on their journey.

Coffee grounds as a fungicide

This is a myth I'm afraid, coffee grounds aren't great at warding off disease. In fact your probably better of using the unbrewed coffee grounds as they're more toxic and acidic, but don't do that, otherwise it could harm your plants.

Try using other forms of natural fungicide, such as horsetail that is a common weed.

Read my article on how to use horsetal as a fungicide

If you’ve used coffee grounds in any other ways or tried some of the methods above, then let me know in the comments below.

If you found this article useful, then subscribe below to stay updated.