Are Coffee Grounds Good for the Garden?

Are coffee grounds a good fertilizer for the garden? Do they have other plant-boosting properties? Do they repel insects or change the pH of the soil? Let’s look at the facts and find out how to use them.

This is part of a series on garden myths where we look at popular garden advice and fact-check it to see how reliable it really is.

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Should I Use Coffee Grounds In the Garden?

When coffee—the beverage— is made, hot water is poured over ground coffee beans, releasing their flavour into the water. The spent coffee grounds are the leftover by-product.

With so many coffee drinkers, imagine how many coffee grounds are generated around the world each day.

A report from the UK says that the average coffee shop produced 20 kg —over 40 pounds—of spent coffee grounds every day. That’s just one shop!

So, is it smart to add them to the garden to help our plants and reduce the waste?

While they have some value, their benefits are often grossly overstated.

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Contents

• Coffee Ground Waste
• Using Coffee Grounds In The Garden
• What Coffee Grounds Don’t Do
• Resources

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Coffee Ground Waste

Two Million Tons of Coffee Grounds Per Year

In North America, it’s estimated that nearly two million tons of coffee grounds are disposed of every year.

And much of that goes to landfill where it contributes to greenhouse gases and other problems.

So, it’s good that people have looked into other uses for coffee grounds—we certainly want to divert them from landfill—but, while they do have beneficial uses in the garden, you can overdo it.

Related: Is Epsom Salt Good For Plants?

Using Coffee Grounds in the Garden

Plant Nutrients

So, what are used coffee grounds good for?

Coffee grounds are a source of plant nutrients. Not to any dramatic levels, but they do provide nutrients such as phosphorus and magnesium and some others.

Coffee Grounds Are A Source of Nitrogen

Coffee grounds are also a good source of nitrogen for composting. Again, nothing breathtaking, but they’re about a 20:1 carbon-to-nitrogen ratio — maybe slightly better than kitchen scraps and grass clippings, but in the same ballpark.

So, despite their brown appearance, they count as “greens” for composting. You can read more about greens and browns here: Composting 101: Slow and Fast Methods.

Do Not Add More Than 20% By Volume

There are warnings about using too many coffee grounds in your compost pile—they should be no more than 20% by volume—according this this paper, Using Coffee Grounds in Landscapes and Gardens – file is in PDF format, which also says that only composted coffee grounds should be used as a soil amendment—not fresh coffee grounds.

Composted coffee grounds can also be used as a mulch, and will provide all the standard benefits of mulches, although here too it is recommended that they be used in moderation, and mixed with other mulches, such as wood chips, because coffee grounds on their own can become compacted, which will not help the soil below.

Coffee Grounds Are Not Magic Beans

So, don’t expect coffee grounds to be magic beans for your garden, but they can provide some benefits if used properly.

There is a lot of noise online claiming coffee grounds have superpowers in the garden. The research indicates they are valuable—along with lots of other organic items—but rumors of their superior qualities have been greatly exaggerated.

What Coffee Grounds Don’t Do

Pests

Despite what you may have heard, there’s no evidence that coffee grounds will repel pests or attract beneficial insects or earthworms.

There’s also little to suggest that they help prevent diseases in the garden—it’s still being studied, but so far it hasn’t been shown.

Soil Alkalinity

Stories of coffee grounds reducing the alkalinity of soil haven’t been supported either.

Coffee grounds can be mildly acidic—which theoretically could affect soil pH (where directly applied)—but, it is shown to be unstable or temporary so that isn’t always the case.

Something we have found is that coffee grounds have been shown to be potentially harmful to seedlings and also slow the growth of some plants. This is a good reason to compost them first with a variety of other materials and not apply them directly.

Related: Plants That Tolerate (or Like) Acidic Soil

Resources

Read More

Learn more about other household items and how they affect the garden:

• Epsom Salt
• Table Salt
• Vinegar
• Baking Soda

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Related: Is Vinegar a Good Weed Killer?

~Melissa the Empress of Dirt ♛