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

Updated: Aug 4, 2022

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?

Studies have shown that used coffee grounds are slightly acidic at 6.5 - 6.8 ph.

Once you've drunk your coffee, you've consumed most of the caffeine and acidity it contains.

Therefore, what's left can be used in the garden.

Plants that love coffee grounds

Used coffee grounds are great for plants that love slightly acidic soils.

Some edible plants that love this slightly acidic environment are:

  • 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 fertilizer when used in your vegetable garden. You can add coffee grounds to your vegetable garden by sprinkling some into your potting mix.

Coffee 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. This 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.

They concluded that coffee grounds weren't that effective as a nitrogen fertilizer.

Coffee grounds as Mulch

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:

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.

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.

My advice is to try it 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.

Coffee grounds as a fungicide

This is a myth I'm afraid. Coffee grounds aren't great at warding off disease.

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

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.

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